Glossary of Terms

AA: atomic absorption spectroscopy.

AAMI grade water: Water meeting quality standards established by the Association for the Advancement of Medical Instrumentation and used mainly for hemodialysis systems.

ABS: alkylbenzene sulfonate.

AOP: advanced oxidation process.

ASTM grade water: SEE reagent grade water.

Avogadro’s number (Avogadro’s Constant): The number of atoms or molecules of a substance contained in one gram mole (a value of the molecular weight of the substance expressed in grams) of that substance. Example: one gram mole of carbon (C), MW=12.00, is 12.00 grams and contains 6.022 x 1023 atoms of C. Oxygen, (O2), being a diatomic molecule, would weigh 32 grams and contain the same number of molecules as 12 grams of Carbon.

absolute filter rating: Filter rating meaning that 99.9 percent (or essentially all) of the particles larger than a specified micron rating will be trapped on or within the filter. Standard test procedures, such as those listed in the ANSI/NSF standards for particulate and cysts reduction by drinking water treatment units, should be used to determine and substantiate absolute filter ratings.

absorbed dose: The amount of a chemical that enters the body of an exposed organism.

absorption: The process of one substance actually penetrating into the structure of another substance. This is different from adsorption in which one substance adheres to the surface of another. SEE ALSO adsorption.

absorption factor: The fraction of a chemical making contact with an organism that is absorbed by the organism.

acceptable daily intake (ADI): Estimate of the largest amount of chemical to which a person can be exposed on a daily basis that is not anticipated to result in adverse effects (usually expressed in mg/kg/day). Same as RfD.

accessible equipment: Water treatment equipment that when installed and operating is exposable and available for proper and thorough cleaning and inspection using only simple tools such as a screwdriver, pliers, or an open-end wrench. Equipment which is easily available for cleaning and inspection without having to use any tools at all is often referred to as readily accessible equipment.

accumulation tank: A vessel or tank which receives and stores product water for use on demand.

accumulation tank: A vessel or tank which receives and stores product water for use on demand.

accuracy: How closely an instrument measures the true or actual value of the process variable being measured or sensed.

acid: A substance which releases hydrogen ions when dissolved in water. Most acids will dissolve the common metals and will react with a base to form a neutral salt and water. An acid is the opposite of a base, has a pH rating lower than 7.0, will turn litmus paper red, and has a sour taste.

acid mine drainage: Drainage of water from areas that have been mined for coal or other mineral ores; the water has low pH, sometimes less than 2.0 (is acid), because of its contact with sulfur-bearing material; acid drainage is harmful because it often kills aquatic organisms.

acid rain: Precipitation which has been rendered (made) acidic by airborne pollutants.

acidic: The condition of water or soil which contains a sufficient amount of acid substances to lower the pH below 7.0.

acidification: The addition of an acid (usually nitric or sulfuric) to a sample to lower the pH below 2.0. The purpose of acidification is to “fix” a water sample so it won’t change until it is analyzed. The sample is then said to be “acidified.”

acidity: The quantitative capacity of a water or solution to neutralize a base. Acidity is usually measured by titration with a standard solution of sodium hydroxide and expressed in ppm or mg/L of calcium carbonate equivalent.

acre-foot: The volume of water which would cover an area of one acre to a depth of one foot. It is equal to 43,560 cubic feet or 325,851 gallons.

acrylic: Ion exchange resin base made of polyacrylate rather than the more common polystyrene.

action level: The concentration of lead or copper in water specified at Code of Federal Regulations 141.80(c) which determines, in some cases, the treatment requirements contained in subpart I of this code that a water system is required to complete.

activated alumina: A medium made by treating aluminum ore so that it becomes porous and highly adsorptive. Activated alumina will remove several contaminants including fluoride, arsenic, and selenium. Activated alumina medium requires periodic cleaning with an appropriate regenerant such as alum, acid, and/or caustic.

activated carbon: A water treatment medium, found in block, granulated, or powdered form, which is produced by heating carbonaceous substances (bituminous coal or cellulose-based substances such as wood or coconut shell) to 700ºC or less in the absence of air to form a carbonized char, and then activating (oxidizing) at 800ºC to 1000ºC with oxidizing gases such as steam and carbon dioxide (oxygen is never used as the oxidizing gas because its reaction with the carbon surface is too rapid and violent) to form pores, thus creating a highly porous adsorbent material.

Activated carbon is commonly used for dechlorination and for reducing trace and soluble materials such as organic chemicals and radon from water.

activated carbon block filter: Activated carbon block is a blend of fine activated carbon (e.g., 80 X 325 mesh activated carbon), water, and a suitable binder (such as polyethylene or a similar material) that is mixed and molded and hardened or extruded to a cartridge filter of any size and shape. Sometimes specialized media are added along with activated carbon to provide customized performances for specific contaminants. The binder is particularly designed and chosen to hold the carbon and other media in a fixed solid matrix, yet, not to plug up the pores of the activated carbon.

Even though the binder does occlude a portion of the adsorption sites, the finer mesh size gives activated carbon block filters faster adsorption kinetics and generally two to four times greater adsorption capacity than equivalent volumes of loose granular activated carbon. Activated carbon block filters typically have a 0.5 to one micron filtration capability, making it also helpful for particulate filtration, insoluble lead reduction, and demonstrating, in some cases, removal of Giardia and Cryptosporidium.

activated silica: A negatively-charged colloidal substance generally formed by combining a dilute sodium silicate solution with a dilute acidic solution (or other activant). Generally used as a coagulant aid.

active transport: An energy-expending mechanism by which a cell moves a chemical across the cell membrane from a point of lower concentration to a point of higher concentration, against the diffusion gradient.

acute: Occurring over a short period of time; used to describe brief exposures and effects which appear promptly after exposure.

acute exposure: A single exposure to a toxic substance which results in severe biological harm or death. Acute exposures are usually characterized as lasting no longer than a day.

acute toxicity: The ability of a substance to cause poisonous effects resulting in severe biological harm or death soon after a single exposure or dose. Also, any severe poisonous effect resulting from a single short-term exposure to a toxic substance.

additive effect: Combined effect of two or more chemicals equal to the sum of their individual effects.

adsorbate: The liquid, gas, or solid substance which is adsorbed as molecules, atoms, or ions.

adsorbent: A water treatment medium, usually solid, capable of the adsorption of liquids, gases, and/or suspended matter. Activated alumina and activated carbon are common adsorbents used in water processing.

adsorption: The physical process occurring when liquids, gases, or suspended matter adhere to the surfaces of, or in the pores of, an adsorbent medium. Adsorption is a physical process which occurs without chemical reaction. SEE ALSO absorption.

aeration: The process whereby water is brought into intimate contact with air by spraying or cascading, or air is brought into intimate contact with water by an air aspirator or by bubbling compressed air through the body of water. Both pressure (closed) aerators and open (gravity) aerators are used. Closed aeration is used chiefly for oxidation; open aeration for degassing.

aerobic: An action or process conducted in the presence of air, such as aerobic digestion of organic matter by bacteria.

aesthetic contaminants: Characteristics of water which affect its taste, odor, color, and appearance (and may affect the objects touched by the water) but which do not in themselves have any adverse health effects in otherwise potable water. Suggested Maximum Contaminant Levels (MCLs) for various aesthetic contaminants in drinking water are part of the National Secondary Drinking Water Regulations issued by the USEPA. These aesthetic standards are advisory only, not enforceable by the USEPA. SEE ALSO drinking water standards.

age tank: A tank used to store a chemical solution of known concentration for feed to a chemical feeder. Also called a day tank.

agglomeration: The collecting or coalescence of dispersed suspended matter into larger masses or flocs which can settle and be filtered from water.

aggregate: A mass or cluster of soil particles, often having a characteristic shape.

agrochemical: Synthetic chemicals (pesticides and fertilizers) used in agricultural production.

air binding: A situation where air enters the filter media. Air is harmful to both the filtration and backwash processes. Air can prevent the passage of water during the filtration process and can cause the loss of filter media during the backwash process.

air check: A device which allows water, but not air, to pass through it. An air check is a typical component of a treatment system using a regenerant eductor.

air dryer: A device used to dry out (desiccate) air by removing the water vapor. An air dryer may be used in ozone generation, for example, to produce higher concentrations of ozone and lessen the production of corrosive nitrous oxides.

air gap: A clear vertical space between the end of the water treatment device’s drain line and the flood level rim of a receptacle which holds water. An air gap is used to prevent cross connection between the water treatment device and a possible source of waste water thereby preventing a reverse flow of water from the sewer into the water supply system. Without an air gap, such reverse flow could occur due to an increase in the pressure in the sewer system or the creation of a negative pressure in the water supply line. Local plumbing codes indicate how wide the air gap needs to be.

air padding: Pumping dry air into a container to assist with the withdrawal of a liquid or to force a liquefied gas such as chlorine out of a container.

air stripping: A technique of aeration for the removal of dissolved gases and volatile substances, often pesticides or hydrocarbon products in water supplies. Large volumes of air are bubbled through the water to remove (strip out) the dissolved gases and volatile substances. The equipment used is a tall, open column with baffling or rock-like materials with air forced upward through a descending sprayed stream of water to be treated. SEE ALSO packed tower aeration.

alarm contact: A switch that operates when some preset low, high, or abnormal condition exists.

alcohol: A class of organic compounds containing one or more hydroxyl (OH^–) groups.

algae: Single-celled or simple multicelled organisms, commonly found in surface water, which produce their own food through photosynthesis. Excessive algae growth may cause the water to have undesirable odors or tastes, and decay of algae can deplete the oxygen in the water.

algal bloom: Sudden, massive growths of microscopic and macroscopic plant life, such as green or blue-green algae, which develop in lakes and reservoirs.

algicide: Any substance or chemical specifically formulated to kill or control algae.

aliphatic: A type of organic compound in which the characteristic chemical groups are linked to a straight or branched carbon chain, as opposed to a carbon ring structure. In complex structures, the chains may also be cross-linked. SEE ALSO aromatic; heterocyclic.

aliphatic hydroxy acids: Organic acids with carbon atoms arranged in branched or unbranched open chains rather than in rings.

aliquot: Portion of a sample.

alkaline: The condition of water or soil which contains a sufficient amount of alkali substances to raise the pH above 7.0.

alkalinity: A measure of concentration of all species in water capable of neutralizing an acid by binding a hydrogen ion, expressed as mg/L or ppm of calcium carbonate equivalents. Alkalinity is measured by titration and is not equivalent to pH.

The most common alkalinity components in naturally occurring surface and groundwater are bicarbonate, carbonate ions and hydroxide ions. As bicarbonate and carbonate ions typically occur in the greatest concentration, the contribution by other species to the measured alkalinity is negligible and often ignored for the purposes of sizing water treatment equipment. SEE ALSO alkalinity tests; pH.

alkalinity tests: There are three different tests used for testing alkalinity. They are usually done in this order:

1. The pH alkalinity test will indicate the presence or absence of hydroxide alkalinity. A pH reading of 8.3 or above indicates the presence of hydroxide alkalinity.

2. The phenolphthalein test measures “P alkalinity” which is made up of all hydroxide alkalinity plus 1/2 of the carbonate alkalinity. P alkalinity is that portion of alkalinity above pH 8.3. Phenolphthalein in water changes color from pink above pH 8.3 to clear at pH 8.3.

3. The Methyl Orange test measures the “M alkalinity” which is the remaining ½ of the carbonate alkalinity plus all of the bicarbonate alkalinity. Methyl orange alkalinity measures total alkalinity of water. The methyl orange endpoint is pH 4.5; no alkalinity exists in water below pH 4.5.

Note: Free carbon dioxide (CO2) gas can exist dissolved in water between pH 4.5 and pH 8.3. Below pH 4.5, CO2 escapes quickly into the environment and above pH 8.3 CO2 becomes carbonate (CO32-) alkalinity. SEE ALSO alkalinity.

alkylaryl sulfonate: A generic term covering a wide range of anionic surfactants and detergent processing aids. The alkylaryl sulfonates of primary interest to the detergent industry are the surfactants classified as linear alkylate sulfonates, usually sodium salts, and the processing aids ammonium, potassium, or sodium salts of toluene, xylene, or cumene sulfonates. They are used to solubilize the active ingredients in some liquid detergents. SEE ALSO alkylbenzene sulfonate; linear alkylate sulfonate; surfactant.

alkylbenzene sulfonate (ABS): A major class of aklylaryl sulfonate surfactants used in detergents; usually a sodium salt. ABS is anionic and high sudsing. Prior to the mid-1960s, the form of ABS most widely used in detergent formulations resisted biodegradation. In 1965, detergent manufacturers voluntarily replaced ABS nationally in household laundry products by a more rapidly biodegradable variety of ABS called linear alkylate sulfonate, or LAS.

SEE ALSO alkylaryl sulfonate; linear alkylate sulfonate; surfactant.

allotrope: One of several possible forms of a substance. Ozone (O3) is a triatomic allotrope of oxygen (O2).

alluvial: Relating to mud and/or sand deposited by flowing water. Alluvial deposits may occur after a heavy rainstorm.

alpha decay: A type of radioactivity where the nucleus of an atomic species changes or disintegrates (decays) via an energetic helium ion (alpha particle) being ejected. Alpha decay produces a daughter nucleus of atomic number two less than the parent and of atomic mass number four less than the parent. SEE ALSO beta-minus decay; beta-plus decay; gamma decay; radioactivity.

alternating current (AC): An electric current that reverses its direction (positive/ negative values) at regular intervals.

alternating system: A dual automatic softener system functioning with one unit in service and one on standby. When a predetermined gallonage of softened water has passed or when a monitor detects hard water breakthrough, the idle or standby unit automatically goes into service. The spent unit then regenerates and becomes the idle/standby unit.

alum: The common name for aluminum sulfate [Al2(SO4)3 • 14H2O] which is often used as a coagulant in water treatment.

alumino silicate: SEE gel zeolite.

aluminum silicate: SEE pumicite.

ambient: Environmental or surrounding conditions.

ambient temperature: Temperature of the surrounding air (or other medium). For example, temperature of the room where a gas chlorinator is installed.

amide: A group of compounds formed by the reaction of an organic acid with ammonia or an amine.

ammonia: An alkaline gas composed of nitrogen and hydrogen (NH3). Ammonia gas is colorless and lighter than air, and exhibits a sharp, intensely irritating odor. Ammonia is extremely soluble in water, reacting to form ammonium hydroxide (NH4OH). At high pH, free ammonia gas (NH3) may be present in water. But, at the pH of most natural waters, ammonia is almost completely ionized as the ammonium ion (NH4+). A typical concentration of ammonia in fresh water rivers and lakes is 0.1 to 1.0 milligrams per liter, expressed as nitrogen (N). Cation exchange in the hydrogen form and adsorption by certain zeolite clays, such as clinoptilolite, may be used to remove ammonium ion from water. At greater than pH 9, air stripping can be used to remove ammonia (NH3) gas from water. Chlorination readily converts ammonia to chloramines (e.g., NH2Cl, NHCl2, and NCl3) that can then be removed from water, as free chlorine is, with activated carbon, except contact times as much as 10 to 100 times that required for free chlorine removal may be required for chloramine removal.

ammonium: The ionic form of ammonia nitrogen (NH4+) that is usable by plants. SEE ALSO ammonia.

amoeba: A single-celled protozoan that is widely found in fresh and salt water. Some types of amoebas cause diseases such as amoebic dysentery.

amperage: The strength of an electric current measured in amperes. The amount of electric current flow, similar to the flow of water in gallons per minute.

ampere: The unit used to measure current strength. The current produced by an electromotive force of one volt acting through a resistance of one ohm.

amperometric: Based on the electric current that flows between two electrodes in a solution.

amperometric titration: A means of measuring concentrations of certain substances in water (such as strong oxidizers) based on the electric current that flows during a chemical reaction. SEE ALSO titrate.

amphoteric: Partly one and partly the other. Capable of reacting chemically as an acid or a base, or as a cation or as an anion, depending on pH.

anaerobic: A condition in which there is no air or no available free oxygen.

anaerobic organism: An organism that can thrive in the absence of oxygen (air), such as bacteria in a septic tank.

analog: The readout of an instrument by a pointer (or other indicating means) against a dial or scale.

analyzer: A device which conducts periodic or continuous measurement of some factor such as chlorine, fluoride, or turbidity. Analyzers operate by any of several methods including photocells, conductivity, or complex instrumentation.

angstrom unit: A unit of length equal to 10-10 meters or 10-8 centimeters or 3.937 X 10-9 inches or .0001 microns. The symbol for angstrom is Å.

animal studies: Investigations using animals as surrogates for humans on the expectation that results in animals are pertinent to humans.

anion: An ion with a negative charge. An anion [such as chloride (Cl-), nitrate (NO3-), bicarbonate (HCO3-), or sulfate (SO42-)] may result from the dissociation of a salt, acid, or alkali.

anion exchange: An ion exchange process in which anions in solution are exchanged for other anions from an ion exchanger. SEE ALSO ion exchange.

anion membrane: SEE ion exchange membrane.

anion softening: Two components are necessary for the formation of boiler scale: a cation and an anion that can react to form an insoluble salt. Examples are calcium or magnesium bicarbonate, which, when heated, form the insoluble carbonate. Anion softening removes the bicarbonate ion and replaces it with the soluble chloride which does not form scale when combined with calcium or magnesium. This process is also known as “dealkalization”.

anionic polymer: A polymer having negatively charged groups of ions; often used as a filter aid and for dewatering sludges.

annular space: A ring-shaped space located between two circular objects, such as two pipes.

anode: The positive pole of an electrolytic system; also the metal which goes into solution in a galvanic cell. Sacrificial anodes of metals such as magnesium, aluminum, or zinc are sometimes installed in water heaters or other tanks to deliberately establish galvanic cells to control corrosion of the tank through the sacrifice of the anode. SEE ALSO sacrificial anode.

antagonism: Interference or inhibition of the effect of one chemical by the action of another chemical.

anthracite: A filter medium produced from crushed anthracite coal and screened to specific mesh sizes.

antibiotic: A substance produced by certain microorganisms or man-made synthetically, that in dilute solutions, can kill or prevent the growth of microorganisms.

antiparticle (antimatter): Any of several species of subatomic particles that are identical in mass to ordinary particles, but opposite in electrical charge or (in the case of the neutron) in magnetic moment. Thus, a positron is an electron with a positive charge, an antiproton is a proton with a negative charge, and an antineutron has no charge but has a magnetic moment opposite to that of a neutron. A photon is its own antiparticle. When an antiparticle collides with its opposite particle (e.g., a collision of an electron and a positron), both particles are annihilated and their masses are converted to photons of equivalent energy. The same is true of other subatomic particles (neutrinos, mesons, etc.), some of which are fantastically short-lived (of the order of billionths of a second).

antiseptic: anti, against + sepsis, decay. Preventing or inhibiting the growth and multiplication of microorganisms, especially pathogenic microorganisms, without necessarily destroying them. SEE ALSO aseptic; aseptic procedure; disinfect; sanitize; sterilize.

appropriative: Water rights to or ownership of a water supply which is acquired for the beneficial use of water by following a specific legal procedure.

appurtenance: Machinery, appliances, structures, and other parts of the main structure necessary to allow it to operate as intended, but not considered part of the main structure.

aquatic: Plants or animal life living in, growing in, or adapted to water.

aqueous: Something made up of, similar to, or containing water; watery.

aquifer: A natural water-bearing geological formation (e.g., sand, gravel, sandstone) which is found below the surface of the earth.

aragonite: A form of calcium carbonate that appears in pearls.

arithmetic mean: An average value of a data set calculated by determining the sum of all the numbers in the data set and dividing by the number of data values within the set.

aromatic: A type of organic compound in which the characteristic chemical groups are linked to a particular type of six-member hexagonal carbon ring which contains three double bonds, typified by benzene. Such rings have peculiar stability and chemical character, and are present in the rather reactive and highly versatile compounds derived from petroleum and cool tar. The name is due to the strong and not unpleasant odor characteristic of most substances of this nature. SEE ALSO aliphatic; heterocyclic.

artesian (aquifer or well): Water held under pressure in porous rock or soil confined by impermeable geologic formations. An artesian well is free-flowing. SEE ALSO confined aquifer.

“as calcium carbonate”—SEE calcium carbonate equivalent.

aseptic: a, not + sepsis, decay. 1. Free or freed from pathogenic organisms and their toxins. 2. A sterile condition, free from germs, infection, and any form of life. SEE ALSO antiseptic; aseptic procedure; disinfect; sanitize; sterilize.

aseptic procedure: A method used to prevent microbial contamination; equipment and tools are cleaned and sanitized, disinfected, or sterilized; personnel wear sanitary or sterilized gloves and sometimes clean caps and masks. SEE ALSO antiseptic; aseptic; disinfect; sanitize; sterilize.

aspirator: A device which creates movement of air, liquids, and granular substances by suction.

assay: A test for a particular chemical or effect.

asymmetric: Not similar in size, shape, form, or arrangement of parts on opposite sides of a line, point, or plane.

atom: The smallest possible component of an element. An atom is comprised of a nucleus (made up of one or more protons and two or more neutrons—except for hydrogen which may have no neutrons) and one or more electrons which revolve around the nucleus. Atoms come together to form molecules.

atomic absorption spectroscopy (AA): A spectroscopy chemical analytical technique used for determining the metal elements in water by measuring the well defined characteristic light wave lengths absorbed by each respective element when the element has been thermally excited into an atomic vapor. The sample to be analyzed is atomized into an atomic vapor by either aspirating the sample into a specific flame (in flame AA) or by vaporization with a tube of graphite that is electrically heated to a temperature between 1500 and 2800ºC (in flameless AA). A light beam of specific characteristic wave lengths is directed through the vapor, into a monochromator that further defines the very small range of wave lengths to be analyzed, and into a detector that measures the amount of light absorbed by the atomized element. Identification of the element is possible because each element has its own well-defined characteristic absorption wave length. The amount of absorbance measured is proportional to the concentration of the element in the sample. SEE ALSO emission spectroscopy; spectroscopy.

attrition: The gradual lessening of the capacity or effectiveness of a medium. This may occur due to friction, sacrificial properties of the medium, chemical attack on the medium, or contaminant saturation of the medium.

automatic dishwasher detergent: A cleaning product designed specifically for use in automatic dishwashers. It must produce little or no suds or foam because too much foam can inhibit the washing action. Its important functions include the following:

• Tie up water hardness minerals to permit the detergent to do its cleaning job.

• Make water wetter (reduce surface tension) to penetrate and loosen soil.

• Emulsify greasy or oily soil.

• Suppress foam caused by protein soils such as egg and milk.

• Help water to sheet off surfaces, thus minimizing water spots.

• Protect china patterns and metals from the corrosive effects of heat and water alone.

Basic ingredients in most automatic dishwasher detergents include:

Surfactant (nonionic)—lowers the surface tension of water so that it will more quickly wet out the surfaces and the soils, thus allowing water to sheet off dishes and not dry in spots. The surfactant also helps remove and emulsify fatty soils like butter and cooking fat. Nonionic surfactants are used because they generally have the lowest sudsing characteristics.

Builder (complex phosphates)—combines with water hardness minerals (primarily calcium and magnesium) and holds them in solution so that the minerals cannot combine with food soils and so that neither the minerals themselves nor the mineral/food soil combination will leave insoluble spots or film on dishes.

Corrosion inhibitor (sodium silicate)—helps protect machine parts, prevent the removal of china patterns, and the corrosion of metals such as aluminum.

Fragrance (optional)—covers the chemical odor of the base product and stale food odors.

Oxidizing agent—helps break down protein soils like egg and milk, aids in removing such stains as coffee or tea, and lessens spotting of glassware.

Processing aids—generally inert materials that allow the active ingredients to be combined into a usable form.

Suds suppressor—controls foam from food soils, especially protein soils.

automatic water softener (or automatic filter): A water softener (or filter) that is equipped with a clock timer which automatically initiates the backwash and/or regeneration process at certain preset intervals of time. All operations, including bypass of treated or untreated water (depending upon design), backwashing, brining, rinsing, and returning the unit to service are performed automatically.

autotrophic: auto, self + trophe, nourishment. Capable of obtaining food or nourishment from simple raw materials. Autotrophic organisms or autotrophs are organic compound producers such as algae, plants, and certain bacteria that use carbon dioxide or carbonates, inorganic nitrogen, water, and an energy source such as photosynthesis from sunlight to make (or synthesize) complex molecules. Opposed to heterotrophic. SEE ALSO heterotrophic.

autotrophs: SEE autotrophic.

available chlorine: A measure of the amount of chlorine available in chlorinated lime, hypochlorite compounds, and other materials that are used as a source of chlorine when compared with that of elemental (liquid or gaseous) chlorine.

available expansion: The vertical distance from the sand surface to the underside of a trough in a sand filter. This distance is also called freeboard.

average: SEE arithmetic mean.

axial flow: SEE longitudinal flow.

axial to impeller: The direction in which material being pumped flows around the impeller or flow parallel to the impeller shaft.

axis of impeller: An imaginary line running along the center of a shaft (such as an impeller shaft).

BIRM: The trade name for a manganese dioxide-coated volcanic aluminum silicate (pumicite) used as an oxidizing-catalyst filter for iron and manganese reduction.

Back Pressure: Pressure which creates resistance against a flow of water.

Back Siphonage: A form of backflow which occurs due to negative pressure.

Backflow: The flow of water in a pipe or line in a direction opposite to the normal flow. Backflow is a problem if there is back siphonage or back pressure causing reverse flow from a cross connection.

Backflow Preventer: A device or system installed in a water line to stop backflow from a nonpotable source.

Background Level: In contaminant monitoring, the average presence of a substance in the environment, originally referring to naturally occurring phenomena.

Backwash: A form of backflow which occurs due to negative pressure.

Bacteria: Single-celled organisms (singular form=bacterium) which lack well-defined nuclear membranes and other specialized functional cell parts and reproduce by cell division or spores. Bacteria may be free-living organisms or parasites. Bacteria (along with fungi) are decomposers that break down the wastes and bodies of dead organisms, making their components available for reuse. Bacterial cells range from about 1 to 10 microns in length and from 0.2 to 1 micron in width. They exist almost everywhere on earth. Despite their small size, the total weight of all bacteria in the world likely exceeds that of all other organisms combined. Some bacteria are helpful to man, others harmful.

Bactericide: Any substance or agent which kills bacteria, both disease causing and nondisease causing. Spores and nonbacterial microorganisms (e.g., algae, fungi, and viruses) are not necessarily killed by a bactericide.

Bacteriostatic: Having the ability to inhibit the growth of bacteria without destroying the bacteria. For example, silver-impregnated activated carbon will reduce bacterial colonization in a bed but not eliminate it.

Baffle: A deflecting barrier to affect the flow pattern of water.

Bailer: A 10- to 20-foot-long pipe equipped with a valve at the lower end. A bailer is used to remove slurry from the bottom or the side of a well as it is being drilled.

Balanced Flow: A flow pattern which is controlled to achieve the flow specified for that water treatment system.

Ballast: The power supply to activate and regulate voltage in an ultraviolet (UV) lamp.

Bar: A unit of pressure. One bar equals 14.5 pounds per square inch (psi), or about 0.987 standard atmospheres.

Barium Fouling: In ion exchange deionization, a condition where the cation exchanger resin becomes coated with a very insoluble coating of barium sulfate. This occurs in the decationization unit when regenerated with sulfuric acid, where a barium-bearing water is being processed. Generally, the remedy must be to replace the cation resin and install upstream water softening to remove the barium prior to the deionization treatment.

Barrier filter: A mechanical filter that physically prevents passage of waterborne solids within a specific particle size range. Barrier filters can include various components such as screens, membranes, or granular media. A common barrier filtration strategy includes the use of a “tortuous path” where the physical pore size of the barrier component is leveraged along with the convoluted flow of water to enable electrostatic and intermolecular forces to act upon the solids allowing rejection of solids smaller than the actual pore size. SEE ALSO mechanical filter; depth filter; tortuous path.

Base: A substance that accepts (binds) hydrogen ions thereby reducing the concentration of free hydrogen ions in solution and raising the pH. A base may be classified as strong or weak, depending on the degree it’s able to attract the hydrogen ion. Hydroxides of metal ions, such as sodium hydroxide and potassium hydroxide, are strong bases. Weak bases include ammonia and alkalinity ions such as carbonate and bicarbonate. Base strength can be determined from pK_b tables, readily available in chemistry reference texts and from reputable sources online. The higher the pK_b number, the stronger the base. SEE ALSO alkalinity.

Base Exchange: See Cation Exchange

Base Metal: A metal (such as iron) which reacts with dilute hydrochloric acid to form hydrogen.

Batch Treatment: A method in which a fixed quantity of water is processed through a single treatment device in a single vessel.

Baume (Be): An arbitrary scale of specific gravities used in the graduation of hydrometers. The Baume measurements were developed by the French chemist Antoine Baume . For liquids heavier than water Be = 145 – (145 specific gravity); for liquids lighter than water, Be = (140 ö specific gravity) – 130.

Bay Salt: A relatively coarse salt made from seawater.

Bead (Resin Bead): In water processing, refers to the spherical shape of individual particles of ion exchange resin products, as compared to the irregular shaped particles of most other granular media products.

Bead Count: A method of evaluating the physical condition (quality) of the resin in a bed by determining the percent of whole, cracked, or broken beads in a wet sample of the resin.

Beaver Fever: Flagellate protozoan which is shed during its cyst stage into the feces of man and animals. When water containing these cysts is ingested, the protozoan causes a severe gastrointestinal disease called giardiasis.

Becquerel (Bq): The SI unit of radioactivity equal to one nuclear disintegration per second. The becquerel supersedes the curie, which equals 3.7 X 10E+10 nuclear disintegrations per second. One becquerel (Bq) equals 27.03 picocuries (pCi).

Bed: The mass or volume of ion exchange resin or other media through which the water passes in the process of water treatment.

Bed Depth: The height of the resin or other media (excluding support material) in a bed, usually expressed in inches or centimeters.

Bed Expansion: The effect produced during backwashing when the resin or other medium becomes separated and rises in the tank or column. Usually expressed as percent of increase of bed depth such as 25 percent, 50 percent, 75 percent, etc.

Bed Volume (BV): A term used as a measurement of a volume of incoming (feedwater) in gallons or liters, equal to (in cubic feet or liters) the volume of ion exchange or filter media product in a tank-including voids. Example: one bed volume for a cubic foot bed would be equal to 7.48 U.S. gallons or 28.3 liters. This term is used mainly in laboratory and in experimental testing rather than in equipment capacity ratings.

Bench Scale: Bench scale testing is usually conducted in the laboratory, but is a simulated test in which conditions are approximate to those with which the item will be used.

Best Available Technology (BAT): The best technology treatment techniques, or other means which the administrator finds, after examination for efficacy under field conditions and not solely under laboratory conditions, that are available (taking cost into consideration). For the purposes of setting MCLs for synthetic organic chemicals, any BAT must be at least as effective as granular activated carbon.

Best Management Practices (BMPs): Structural, nonstructural, and managerial techniques that are recognized to be the most effective and practical means to control nonpoint source pollutants yet are compatible with the productive use of the resource to which they are applied. BMPs are used in both urban and agricultural areas.

Beta-minus decay: A type of radioactivity where the nucleus of an atomic species changes or disintegrates (decays) via negatron emission an energetic negative electron being emitted. Beta-minus decay produces a transformed daughter nucleus of one lower atomic number and the same mass number.

Beta-plus decay: A type of radioactivity where the nucleus of an atomic species changes or disintegrates (decays) via an energetic positron (a positive electron antiparticle) being created and emitted, along with a neutrino. Beta-plus decay produces a transformed daughter nucleus of one lower atomic number and the same mass number.

Bias: An inadequacy in experimental design that leads to results or conclusions not representative of the population under study.

Bicarbonate: The HCO³ ion.

Bicarbonate Alkalinity: The alkalinity of a water due to the presence of bicarbonate ions (HCO³-).

Bicarbonate Hardness: The hardness of a water due to the presence of calcium and magnesium bicarbonates, usually the major component of carbonate hardness or total hardness. Bicarbonate hardness is often referred to simply as carbonate hardness.

Bicarbonate of Soda: A common name, along with baking soda, for sodium bicarbonate (NaHCO³).

Bioaccumulation: The retention and concentration of a substance by an organism.

Bioassay: Test which determines the effect of a chemical on a living organism.

Biochemical Oxygen Demand: The amount of oxygen (measured in mg/L) required in the oxidation of organic matter by biological action under specific standard test conditions. Widely used to measure the amount of organic pollution in waste water and streams.

Biocide: A chemical which can kill or inhibit the growth of living organisms such as bacteria, fungi, molds, and slimes. Biocides can be harmful to humans, too. Biocides kill spores of living organisms also, and since spores are the most resistant of all life forms, a biocide may be properly defined as a sterilizing agent.

Bioconcentration: The accumulation of a chemical in tissues of an organism (such as fish) to levels that are greater than the level in the medium (such as water) in which the organism resides.

Biodegradable: Subject to degradation (breakdown) into simpler substances by biological action. For example: the breakdown of detergents, sewage wastes, and other organic matter by bacteria.

Biodegradation: Decomposition of a substance into more elementary compounds by the action of microorganisms such as bacteria.

Biofilm: An accumulation of sessile microbial growth imbedded in a film of adhesive polymer and attached on the surface of a support material, such as the interior surface of water pipe or water storage vessels. Bacteria within the film may be protected from the action of disinfectants and sanitizers.

Biogas (Methane): A colorless, odorless, flammable gas consisting of the hydrocarbon (CH⁴) and resulting from the decay of vegetable matter or manure due to the action of anaerobic bacteria in swampy land, closed landfills, or sewage disposal plants. Methane is also known as biogas and it is called swamp gas when produced in marshy land. Coal miners know methane as one of the main components of fire-damp and also of coal-gas. Methane dissolved in water gives the water a milky cast, and since it is flammable, methane must be safely aerated and vented to the atmosphere during removal.

Biological Growth: The activity and growth of any and all living organisms.

Biologically Activated Carbon: Activated carbon which maintains active microbiological growth to aid in the degradation and reduction of organics that have been adsorbed on the surface and in the pores of activated carbon. Biological activation of carbon can be enhanced by enriching the feedwater with air or ozone.

Bioremediation: A process of adding nutrients to ground water to speed up the natural process in which bacteria breakdown gasoline and other petrochemicals into harmless compounds.

Biostat: An agent similar to a bacteriostat but prevents the growth of (but not necessarily destroys) all living organisms.

Biota: An overall term for all living organisms in an ecosystem.

Biotransformation: Conversion of a substance into other compounds by organisms; includes biodegradation.

Bitterns (Mother Liquor): 1. Residual brines, containing chiefly calcium and magnesium chlorides, obtained after the salt has been crystallized and removed from solution. The term “mother liquor” is widely used when salt is produced by use of vacuum pan and gainer operations. In the solar salt evaporation process, the term “bitterns” is often used in place of the term “mother liquor”.

2. A solution substantially freed from undissolved matter by a solid/liquid separation process, such as filtration or decanting.

Bivalent: Having a valence of two. Also called divalent.

Black Water: Liquid and solid human body waste and the carriage water generated through toilet usage.

Blank: A bottle containing only dilution water or distilled water; the sample being tested is not added. Tests are frequently run on a sample and a blank and the differences are compared.

Bleach: A strong oxidizing agent and disinfectant formulated to break down organic matter and destroy biological organisms. Commonly refers to a 5.25 percent nominal solution of sodium hypochlorite (household bleach) which is equivalent to 3 percent to 5 percent available free chlorine (strength varies with shelf life). Sodium hypochlorite is also available commercially in concentrations of between 5 percent and 15 percent available chlorine. Dry bleach is a dry calcium hypochlorite with 70 percent available chlorine.

Blind Spots: Places in the filter medium or membrane where no filtration takes place.

Blinding: The reduction or shutting off of flow due to filter medium or membrane fouling.

Block Carbon (Activated Carbon Block Filter): Activated carbon block is a blend of fine activated carbon (e.g., 80 X 325 mesh activated carbon), water, and a suitable binder (such as polyethylene or a similar material) that is mixed and molded and hardened or extruded to a cartridge filter of any size and shape. Sometimes specialized media are added along with activated carbon to provide customized performances for specific contaminants. The binder is particularly designed and chosen to hold the carbon and other media in a fixed solid matrix, yet, not to plug up the pores of the activated carbon. Even though the binder does occlude a portion of the adsorption sites, the finer mesh size gives activated carbon block filters faster adsorption kinetics and generally two to four times greater adsorption capacity than equivalent volumes of loose granular activated carbon. Activated carbon block filters typically have a 0.5 to 1 micron filtration capability, making it also helpful for particulate filtration, insoluble lead reduction, and demonstrating, in some cases, removal of Giardia and Cryptosporidium.

Blowby: 1. The technique sometimes used for recycling concentrate back to the feed.

2. Contaminant leakage through or by the water treatment device.

Blowdown: The withdrawal of water containing a high concentration of solids from an evaporating water system (such as a boiler system) in order to maintain the solids-to-water concentration ratio within specified limits. Blowdown is normally performed in boiler and cooling water operations. The term may also refer to removal of other solutions of undesirable quality from a system or vessel.

Blue-Green Algae (Cyanobacteria): Single-celled organisms (singular=cyanobacterium) similar to bacteria, except cyanobacteria contain the green pigment chlorophyll (as well as other pigments), which traps the energy of sunlight and enables these organisms to carry on photosynthesis. Cyanobacteria are autotrophic producers of their own food from simple raw materials, whereas bacteria are heterotrophic decomposers of the wastes and bodies of other organisms. Cyanobacteria were formerly known as blue-green algae. Blooms or population explosions of cyanobacteria cause water pollution. Some cyanobacteria-like bodies (CLBs) have been associated with causing waterborne diarrheal illnesses.

Boiler Water: A representative sample of the water or steam condensate circulating in a boiler system, taken after the generated steam has been separated and before the incoming feedwater or any added chemical has become mixed with the sample to change its composition. The quality of boiler feedwater must be carefully controlled to limits depending on the boiler pressure and horsepower rating.

Bone Char: A black pigment substance, with a carbon content of about 10 percent, made by carbonizing animal bones. Bone char is used for decolorizing sugar and water treatment. It has been used as a selective anion exchanger for fluoride and arsenic reduction.

Bonnet: The cover on a gate valve.

Bored Well: A shallow (10 to 100 feet or 3 to 30 meters) large-diameter well (8 to 36 inches or 20 to 90 cm.) constructed by hand-operated or power-driven augers.

Bottled Artesian Water: Bottled water from a well tapping a confined aquifer in which the water level stands above the water table. Bottled artesian water shall meet the requirements of bottled natural water.

Bottled Distilled Water: Bottled water which has been produced by a process of distillation and meets the definition of purified water in the most recent edition of the United States Pharmacopeia.

Bottled Fluoridated Water: Bottled water containing fluoride. The label shall specify whether the fluoride is naturally occurring or added. Any water which meets the definition of bottled fluoridated water shall contain not less than 0.8 milligrams per liter fluoride ion and otherwise comply with the Food and Drug Administration (FDA) quality standards in Section 103.35(d)(2) of Title 21 of the Code of Federal Regulations (CFR).

Bottled Mineral Water: Bottled water containing fluoride. The label shall specify whether the fluoride is naturally occurring or added. Any water which meets the definition of bottled fluoridated water shall contain not less than 0.8 milligrams per liter fluoride ion and otherwise comply with the Food and Drug Administration (FDA) quality standards in Section 103.35(d)(2) of Title 21 of the Code of Federal Regulations (CFR).

Bottled Natural Water: Bottled spring, mineral, artesian, or well water which is derived from an underground formation, and is not derived from a municipal system or public water supply.

Bottled Spring Water: Bottled water derived from an underground formation from which water flows naturally to the surface of the earth, or is pumped through a borehole from a spring source. Bottled spring water shall meet the requirements of bottled natural water.

Bottled Water: Water that is placed in a sealed container or package, and is offered for sale for human consumption or other consumer uses. Bottled water may be with or without natural or added carbonation, and may be prepared with added flavors, extracts, and/or essences derived from a spice or fruit and comprising less than one percent by weight of the final product. Said products shall contain no sweeteners, acidulants, or additives other than said flavors, extracts, or essences.

Bottled Water Plant: Any place or establishment in which bottled water is prepared for sale.

Brackish Water: Water containing dissolved solids in the range of 1,000 to less than 15,000 parts per million.

Brake Horsepower: 1. The horsepower required at the top or end of a pump shaft (input to a pump).

2. The energy provided by a motor or other power source.

Brass: A metal alloy of copper, zinc, and usually some lead. Brass is harder and stronger than copper because of its zinc content; lead contributes malleability and ductility. Machined brass plumbing products are often made from Copper Development Association (CDA) 360 series brass which contains about 65 percent copper, 32 percent zinc, and 3 percent lead.

Breakpoint Chlorination: A chlorination procedure in which the chlorine is added until the chlorine demand is satisfied and a chlorine residual occurs. The breakpoint is reached when a free chlorine residual is achieved. Further additions of chlorine produce a free chlorine residual proportional to the amount added.

Breakthrough: The first appearance in the product water of an amount of the contaminant which exceeds the design performance criteria.

Bridging: 1. Bridging occurs in water softening when salt sticks together to form one large solid mass of pellets, or by the salt caking in a dry-salt brine tank which causes failure of the liquid or brine beneath the dry salt to become saturated. The result of bridging is insufficient salt in the regenerant solution to properly regenerate the cation resin.

2. The ability of particles to form a crustlike film over void spaces within a filter medium or membrane.

Brine: A strong solution of salt(s) (usually sodium chloride and other salts too) with total dissolved solids concentrations in the range of 40,000 to 300,000 or more milligrams per liter. Potassium or sodium chloride brine is used in the regeneration stage of cation and/or anion exchange water treatment equipment. Sodium chloride brine saturation in an ion exchange softening brine tank is about 26 percent NaCl by weight at 60 degrees Fahrenheit.

Brine Collector: A device used to gather and retrieve brine from a brine tank or ion exchange bed.

Brine Draw: Usually means the process of drawing a brine solution into a cation or anion exchange water treatment device during regeneration.

Brine Ejector (Eductor): A device used to draw (or educt) brine from a brine tank and force (or eject) it into a cation and/or anion water treatment device. Usually a component of the unit’s control valve.

Brine Tank Grid: A perforated platform in the bottom section of a brine tank of home water softeners which creates a zone where water can come in contact with the lower side of the dry salt stored above. As the water reaches up to the salt layer, it creates the brine makeup for regeneration.

Brinelling: Tiny indentations (dents) high on the shoulder of a water pump’s bearing race or bearing. A type of bearing failure.

British Thermal Unit (BTU): The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

Bromine (Br): A nonmetallic usually univalent or pentavalent element that lies between chlorine and iodine in the halogen group of the periodic table. Bromine has been used in swimming pools for disinfection and in cooling towers as a biocide, but its use in drinking water as a primary disinfectant has been limited because of uncertain effectiveness in the presence of organic material, ammonia, and other amines.

Brownian Movement: The random movement of microscopic particles suspended in a fluid.

Bubble Size: The average diameter of the gas (e.g., ozone or air) bubbles discharged from a diffuser at the bottom of the contactor in an ozone or aeration system. Generally, the finer the bubble size and the longer the bubble resides (contacts) within the water, the greater will be the transfer of air or ozone to the water.

Buffer: A chemical substance which stabilizes pH values in solutions.

Buffer Capacity: A measure of the capacity of a solution or liquid to neutralize acids or bases. This is a measure of the capacity of water for offering a resistance to changes in pH.

Buffer Strips: Strips of grass or other close-growing vegetation that separate a waterway (ditch, stream, creek) from an intensive land use area (subdivision, farm); also referred to as filter strips, vegetated filter strips, and grassed buffers.

Builder: A material that upgrades or protects the cleaning efficiency of the surfactant. Several types of compounds, with different performance capabilities, are used. Builders have a number of functions, principally inactivation of water hardness. This is accomplished either by sequestration, i.e., holding hardness minerals in solution, by precipitation, or by ion exchange. Complex phosphates are common sequestering builders. Sodium carbonate is a precipitating builder. Sodium aluminosilicate is an ion exchange builder. Other functions of builders are to supply alkalinity to assist cleaning, especially of acid soils, to provide buffering so that alkalinity is maintained at an effective level, to aid in keeping removed soil from redepositing during washing, and to emulsify oily and greasy soils.

Built Detergent: A cleaning product containing both surfactant and builder. Home laundering makes use of built detergents almost exclusively because of their effective performance. Ingredients used in formulations along with surfactant and builder include fluorescent whitening agent, antiredeposition agent, corrosion inhibitor, suds control agent, oxygen bleach, colorant, fragrance, enzyme, bluing, and processing aids. Not all of these ingredients are used in every built detergent. Inclusion of antiredeposition and whitening agents, corrosion inhibitor, colorant, fragrance, and processing aids is customary. Complex phosphates (especially sodium tripolyphosphate), sodium carbonate, and sodium silicate are the builders most commonly used. (Sodium silicate is also a corrosion inhibitor.) Borax and sodium citrate are used to a lesser extent. Built detergents may be granular or liquid in form and produce high, medium, or low suds. Since built detergents are designed for doing laundry, they are classified as laundry detergents. They are also considered heavy duty. Those that are high sudsing are adapted to many nonlaundry household cleaning tasks, and are termed “all purpose.”

Built Soap: A combination of soap and builder designed for general purpose use, especially laundering. It also usually contains fluorescent whitening agent, colorant, and fragrance. The granule form of built soap represented a major development and, by the late 1930s, had largely replaced laundry soap in bar and chip form. However, it still presented the classical soap problems in hard water, and thus built soap granules rapidly lost market share when built detergents were marketed in the late 1940s. Today, built soaps are in very limited distribution.

Burnt Lime (CaO): A calcined chemical material, calcium oxide. Lime is used in lime and in lime and soda ash water treatment, but must first be slaked to calcium hydroxide [Ca(OH)²]. Lime is also called burnt lime; calyx; fluxing lime; quicklime; unslaked lime.

C factor: A factor or value used to indicate the smoothness of the interior of a pipe. The higher the C factor, the smoother the pipe, the greater the carrying capacity, and the smaller the friction or energy losses from water flowing in the pipe. To calculate the C factor, measure the flow, pipe diameter, distance between two pressure gauges, and the friction or energy loss of the water between the gauges.

CA: Cellulose acetate

CAG: Carcinogen Assessment Group

CAP Grade Water: Water which meets standards established by the College of American Pathologists. The standards cover three types of laboratory grade water: clinical, cell or tissue, and cultural.

CAS Registration Number: A number assigned by the Chemical Abstracts Service to identify a chemical.

CLBs: Cyanobacteria-like bodies

COD: Chemical oxygen demand

CSMR: SEE Chloride/Sulfate Mass Ratio

CT or CTcalc: The product of “residual disinfectant concentration” (C) in mg/L determined before or at the first customer, and the corresponding “disinfectant contact time” (T) in minutes, i.e., “C” X “T”. If a public water system applies disinfectants at more than one point prior to the first customer, it must determine the CT of each disinfectant sequence before or at the first customer to determine the total percent inactivation or “total inactivation ratio.” In determining the total inactivation ratio, the public water system must determine the residual disinfectant concentration of each disinfection sequence and corresponding contact time before any subsequent disinfection application point(s). “CT99.9” is the CT value required for 99.9 percent (3-log) inactivation of Giardia lamblia cysts. CT99.9 values for a variety of disinfectants and conditions appear in Tables 1.1-1.6, 2.1, and 3.1 of section 141.74(b)(3) in the code of Federal Regulations.

CT99.9: The inactivation ratio. The sum of the inactivation ratios, or total inactivation ratio shown as ä = (CTcalc) / (CT99.9) is calculated by adding together the inactivation ratio for each disinfection sequence. A total inactivation ratio equal to or greater than 1.0 is assumed to provide a 3-log inactivation of Giardia lamblia cysts.

Caisson: A structure or chamber in water well construction which is usually sunk or lowered by digging from the inside. Used to gain access to the bottom of a stream or other body of water.

Calcite: 1. Calcium carbonate (CaCO₃).

2. A trade name for finely ground grades of marble or limestone, very high in calcium carbonate, which are used to raise the pH reading (reduce the acidity) of low pH (acidic) water or to filter out sediment.

Calcium (Ca): One of the principal elements making up the earth’s crust. Calcium compounds, when dissolved, make water hard. The presence of calcium in water is a factor contributing to the formation of scale and insoluble soap curds which are a means of clearly identifying hard water.

Calcium Carbonate: [CaCO₃] A chemical compound found in nature as calcite (in limestone, marble, and chalk) and aragonite (in pearls) and in plant ashes, bones, and many shells.

Calcium Carbonate Equivalent: The weight or concentration of calcium carbonate (CaCO₃) that would have the same number of ionic charges (and therefore have equal chemical value) to a certain amount of another material. For example, the weight of a material divided by the equivalent weight of this material equals the number of ionic or valence charges (reactive protons), multiplied by the equivalent weight of CaCO₃ (the weight per ionic charge of CaCO₃) equals the calcium carbonate equivalents for this original material. The hardness in water that is caused by calcium, magnesium, and other cations is usually described in terms of the calcium carbonate equivalent. For example, the concentration of calcium ions (i.e., [Ca²⁺] can be multiplied by 50/20 or 2.5 (the ration of CaCO₃‘s equivalent weight to Ca²⁺‘s equivalent weight) to give [Ca²⁺] as equivalent CaCO₃. Therefore, 100 ppm of calcium equals 250 ppm of calcium as calcium carbonate. Similarily, 10 ppm of magnesium equals 50/12.15 x 10 or 41 ppm of magnesium as calcium carbonate. The total calcium plus magnesium hardness of this water would be 250 + 41 = 291 calcium carbonate equivalent (÷ 17.1 gpg/ppm = 17 grains per gallon CaCO₃ total hardness). The process of converting to calcium carbonate equivalents makes it possible to compare various minerals. Calcium carbonate equivalent conversion calculations have been completed for other compounds and are shown in an Appendix to WQA’s Glossary of Terms textbook.

Calcium Chloride: [CaCl₂] A soluble salt, some uses of which are similar to those of sodium chloride. Since its most striking property is its ability to draw moisture from the air and so dissolve itself, it is often used as an air dryer and as a de-icing salt.

Calcium Hydrate: SEE hydrated lime

Calcium Hypochlorite: [Ca(OCl)₂] A chemical compound used as a bleach and a source of chlorine in water treatment. Commercial grades contain 70 percent available chlorine. It is specifically useful because it is stable as a dry powder and can be formed into pellets.

Calcium Oxide: SEE lime

Calcium Sulphate Saturation: The point beyond which any further addition of calcium sulfate to a given solution will cause precipitation. CaSO₄ precipitation occurs in decationization when resin is regenerated with too strong an H₂SO₄ acid solution. Also can occur in electrodialysis systems.

Calibration: A procedure which checks or adjusts an instrument’s accuracy by comparison with a standard or reference.

Calorie: The amount of heat required to raise the temperature of one gram of water one degree Celsius (Centigrade).

Calyx: SEE lime

Cancer: A disease characterized by the rapid and uncontrolled growth of aberrant cells into malignant tumors.

Capacity: SEE Rated Capacity

Capacity Curve: As relates to ion exchange, a graph of the ion exchange capacity vs. regenerant levels for an ion exchange unit or system.

Capillary Action: A phenomenon in which water or other liquids will rise above the normal liquid level in a tiny tube or capillary due to the attraction of the molecules in the liquid for each other and for the walls of the tube.

Capillary Forces: The molecular forces which cause the movement of water through very small spaces.

Capillary Fringe: The porous material just above the water table which may hold water by capillarity (a property of surface tension that draws water upwards) in the smaller void spaces.

Capital Costs: Costs (usually long-term debt) of financing construction and equipment. Capital costs are usually fixed, one-time expenses which are independent of the amount of water produced.

Carbon (C): An element which is found in almost all living or formerly living matter including plants, proteins, organics, and hydrocarbons. Carbon combines readily with oxygen to form carbon dioxide (CO2). In water treatment applications, the term “carbon” is sometimes used as a short reference for activated carbon.

Carbon Block: SEE Activated Carbon Block Filter

Carbon Chloroform Extract (CCE): A procedure used to measure of the organic matter in a water. To get this measurement, the matter adsorbed from the water by activated carbon is extracted from the carbon by using a specific standardized procedure involving chloroform.

Carbon Chloroform extract (CCE): A measure of the organic matter in a water. To get this measurement, the matter adsorbed from the water by activated carbon is extracted from the carbon by using a specific standardized procedure involving chloroform.

Carbon Dioxide: A naturally-occurring gas (CO₂) present in the atmosphere and formed by the decay of organic matter. Carbon dioxide is naturally present in air to the extent of 0.03 percent by volume and 0.05 percent by weight, in rainwater at 2 to 6 ppm, and in most water supplies from zero to 50 ppm. Carbon dioxide is the gas in carbonated beverages. Dissolved in water, it can form carbonic acid (H₂CO₃).

Carbonaceous: Containing carbon and derived from organic substances such as coal, coconut shells, and wood.

Carbonaceous Exchanger: Cation ion exchangers of limited capacity, prepared by the sulfonation of coal, lignite, or peat. Often contain both strong acid and weak acid groups.

Carbonate: The CO₃^2- ion.

Carbonate Alkalinity: Alkalinity due to the presence of the carbonate ion (CO₃^2-).

Carbonate Hardness (temporary hardness): The hardness content in water associated with bicarbonate and carbonate alkalinity. Carbonate hardness will form a precipitate when heated or evaporated due to thermal decomposition of the bicarbonate ion to carbonate ion and the loss of CO₂. SEE ALSO hardness; noncarbonate hardness; total hardness.

Carbonated Water: SEE Soda Water

Carboxylic group (COOH): A specific acidic group having a chemical formula that contributes cation exchange ability to some resins. Sometimes called weak acid cation exchangers.

Carcinogen: Any substance which tends to produce cancer in an organism.

Carcinogenic: Cancer-producing.

Carry-over: SEE Entrainment

Cartridge: Any removable preformed or prepackaged component containing a filtering medium, ion exchanger, membrane, or other treatment material which fits inside a housing to make up a cartridge filter. Also called an element.

Cartridge Filter: A device often used for single faucet water treatment, made up of a housing and a removable cartridge (element). In high flow rate commercial applications, the elements are clustered in a large housing, and the elements are cleanable and reusable. In residential use, disposable elements are used.

Catalyst: A substance that changes the speed or yield of a chemical reaction without being consumed or chemically changed by the chemical reaction.

Catalyst Media: Those filter media which can cause certain reactions to occur in water treatment, such as activated carbon, calcite, manganese greensand, magnesium oxides, and dissimilar metal alloys.

Catalyst/Oxidizing Filters: A class of media bed filters which contain manganese treated greensand, zeolites, or pumicites.

Catalytic Activated Carbon: Activated carbon with modified surface properties that enhance the functionality of the activated carbon in converting the oxidation state of various elements. For example, with hydrogen sulfide (H2S), the sulfide ion (S-) is adsorbed and then converted on the catalytic carbon to elemental sulfur (S0) and sulfate ion (SO4 –). Once the sulfide is adsorbed and converted, it is desorbed and the site is restored. For these reactions to occur, excess dissolved oxygen is required in the water and a minimum empty bed contact time (EBCT) of five minutes may be necessary.

Catalytic Ozone Destructor: A type of ozone destruction unit that uses a catalyst to enhance the performance of the off-gas treatment system.

Catalyze: To act as a catalyst. Or, to speed up a chemical reaction.

Catalyzed: To be acted upon by a catalyst

Cathode: A negative pole of an electrolytic system; an electrode where reduction occurs.

Cathodic Protection: The sacrificial use of one metal (the sacrificial anode) to protect against the surface corrosion of another surface. Usually a galvanic cell is established by the more easily corroded sacrificial anode or by impressed current which causes the other metal surface to become cathodic and thereby protected.

Cation: A positively charged ion in an electrolyte solution, attracted to the cathode under the influence of a difference in electrical potential. Sodium ion (Na+) is a cation.

Cation Exchange: The ion exchange process in which cations in solution are exchanged for other cations available from an ion exchange product. Formerly called base exchange.

Cation Exchange Resin: An ion exchange material possessing reverse exchange ability for cations. Sulfonated polystyrene copolymer divinylbenzene exchange resin is used almost exclusively today in ion exchange water softeners. A cation exchange resin may be called a cation exchanger or a base exchanger.

Cation Exchange Resin: An ion exchange material possessing reverse exchange ability for cations. Sulfonated polystyrene copolymer divinylbenzene exchange resin is used almost exclusively today in ion exchange water softeners. A cation exchange resin may be called a cation exchanger or a base exchanger.

Cation Exchange Water Softener: An equipment unit capable of reducing water hardness by the cation exchange process.

Cation Membrane: SEE Ion Exchange Membrane

Cation exchanger: SEE cation exchange resin

Cationic Polymer: A polymer having positively charged groups of ions; often used as a coagulant aid.

Caustic: 1. Caustic soda (NaOH) or any compound chemically similar to caustic soda.

2. Any substance capable of burning or destroying animal flesh or tissue. The term is usually applied to strong bases.

Caustic Lime: SEE Hydrated Lime

Caustic Soda: SEE Sodium Hydroxide

Cautsic Lime: SEE Hydrated Lime

Cavitation: The formation and collapse of a gas pocket or bubble on the blade of an impeller or the gate of a valve. The collapse of this gas pocket or bubble drives water into the impeller or gate with a terrific force that can cause pitting on the impeller or gate surface. Cavitation is accompanied by loud noises that sound like someone is pounding on the impeller or gate with a hammer.

Cellulose Acetate (CA) & Cellulose Triacetate (CTA): A cellulose ester obtained by introducing the acetyl radical (CH₃CO^–) of acetic acid into cellulose (as cotton or wood fibers) to produce a tough plastic material which is used to make the cellulosic-type of semipermeable reverse osmosis membranes.

Cellulose Ion Exchangers: Cellulose-based products which have been cross-linked and then modified with either anion or cation groups capable of selective ion exchange. Cellulose materials have some natural weak acid functionality.

Cellulose triacetate (CTA): SEE Cellulose Acetate

Celsius: SEE Centigrade

Centigrade: A temperature scale in which 100 degrees is the boiling point and zero degrees the freezing point for water at sea level.

Centimeter: One one-hundredth (1/100) of a meter (m).

Central Nervous System: Portion of the nervous system which consists of the brain and spinal cord; CNS.

Centrate: The water leaving a centrifuge after most of the solids have been removed.

Centrifugal Pump: A pump containing a rotating impeller or rotating vanes mounted on a shaft in a casing and turned by a power source. The rotating impeller uses centrifugal force to deliver water in a steady stream (without pulsations) to the point-of-use.

Centrifuge: A mechanical device that uses centrifugal or rotational forces to separate solids from liquids.

Certification: 1. As used in relation to WQA equipment performance testing, the determination that a representative sample of the equipment model to be certified has met the requirements of the respective test standard.

2. As used in relation to WQA educational services, the granting of certified status (Certified Water Specialist; Certified Sales Representative; Certified Installer) to individuals who have passed the WQA certification examinations.

Challenge Water: Water specifically prepared for testing the performance of water treatment equipment products. Challenge water for each type of equipment is specifically defined in the individual equipment testing standards such as those established by the Water Quality Association and the National Sanitation Foundation International.

Channeling: The higher and unbalanced flow of water or regenerant through a limited number of passages in a filter or ion exchanger bed, as opposed to an evenly distributed flow through all passages in the bed. Channeling results in the greater flow of liquid through passages of lower resistance which can occur in fixed beds or columns of media particles due to nonuniform packing, irregular sizes and shapes of the particles, gas pockets, wall effects, fouling of the bed and resulting plugging of many passages, poor distributor design, low flow rates, faulty operations procedures, insufficient backwash, and other causes.

Charcoal: An adsorbent carbon product which has about one-third the surface area of activated carbon.

Charged Polysulfone Membrane: Normal (uncharged) polysulfone (PS) membranes contain physical pores that can pass salts; they are used in ultrafiltration water treatment. Charged PS membranes have been chemically sulfonated to create the ability to reject dissolved salts. The sulfonation process permanently affixes sulfonate (SO3-) groups on the membrane surface, in a process similar to that used to give cation exchange resins their charge characteristics. These negatively charged sites repel anions, and indirectly repel the cations also due to the cations’ attraction to anions in the concentrate solution. Charged PS membranes have salt rejection and chlorine tolerance characteristics similar to cellulosic membranes, and offer a permeate flux rate comparable to thin-film composite membranes. However, charged PS membranes are more easily fouled by any divalent or trivalent cations, such as calcium, magnesium, or iron existing in the feedwater.

Check Valve: A valve which will allow water to pass in one direction but will close and prevent flow (backflow) in the opposite direction.

Chelating Agent: A chemical or complex that interacts with an ion, usually a metal causing the ion to join that chemical or complex by both ordinary and coordinate valence forces. Such linkages result in the formation of one or more heterocyclic rings in which the metal atom is part of the ring. Commercially available chelating agents may be used to “tie up” and inactivate water hardness and other metallic ions in water.

Chelating ion exchanger: A special selective resin which will adsorb one metal ion to the exclusion of any other present in a stream of water.

Chelation: The process of forming complex chemical compounds in which certain metal ions are bound into stable ring structures, keeping the ions in solution and eliminating or reducing normal (and often undesirable) effects of the ions. Similar to the process of sequestration.

Chemical Claim: A system used to introduce and feed, on a proportional basis, a chemical solution (such as chlorine, caustic, fluoride, iodine, etc.) into a stream of water.

Chemical Lime: SEE calcium oxide; lime

Chemical Oxygen Demand (COD): An indirect measure of the amount of oxygen used by inorganic and organic matter in water. The measure is a laboratory test based on a chemical oxidant and, therefore, does not necessarily correlate with biochemical oxygen demand.

Chemical Precipitation Softening: SEE lime softening; lime-soda ash softening

Chemical Stability: Resistance to attack by chemical action. This term is often applied to the resistance of ion exchange resins to breakdown due to contact with aggressive solutions.

Chemically Reactive Media: Those granular or bead form materials used in filtration processes which can react chemically with constituents in the water and serve to modify the water quality, such as calcite, in pH modification; or as a catalyst to initiate chemical reactions such as manganese greensand, pyrolusite, activated carbon, and dissimilar metal alloy products.

Chemisorption: A process related to adsorption in which atoms or molecules of reacting substances are held to the surface atoms of a catalyst by electrostatic forces having about the same strength as chemical bonds. Chemisorption differs from physical adsorption chiefly in the strength of bonding, which is much greater in chemisorption than in adsorption.

Chiller: Cropland preparation by a special implement (chisel) that avoids complete inversion of the soil (as occurs with conventional moldboard plowing). Chisel plowing can leave a protective cover of crop residues on the soil surface that helps prevent erosion and improve infiltration.

Chloramines: Chemical complexes formed from the reaction between ammonia and chlorine being used to disinfect many municipal water supplies. Unlike chlorine, chloramines do not combine with organics in the water to form potentially dangerous trihalomethanes (THMs). Chloramines can exist in three forms: 1. monochloramine (NH2Cl) 2. dichloramine (NHCl2) 3. nitrogen trichloride (NCl3). The proportions of the chloramines depend on the physical and chemical properties of the water. Water containing chloramines may not be used for fish or for kidney dialysis applications.

Chloride/Sulfate Mass Ratio (CSMR): The relative ratio of the concentration of chloride ions (Cl ^–) to sulfate ions (SO₄^2-), calculated by dividing the Average Chloride Level by the Average Sulfate Level in the water. The resulting number is used in predicting the potential for aggravating galvanic corrosion. A common example is lead corrosion in plumbing systems containing lead pipe, solder or other leaded components. Current research indicates that a CSMR > 0.2 is grounds for significant corrosion concern, especially at low levels of Total Alkalinity. SEE ALSO Alkalinity, Chloride, Corrosion, Lead, Sulfate

Chlorinated Polyvinyl Chloride (CPVC): A rigid, high-strength thermo-plastic polymer (polyvinyl dichloride) that is practically inert toward water, inorganic reagents, hydrocarbons, and alcohols over a broad temperature range, used for pipe and pipe fittings.

Chlorination: The treatment process in which chlorine gas or a chlorine solution is added to water for disinfection and control of microorganisms. Chlorination is also used in the oxidation of dissolved iron, manganese, and hydrogen sulfide impurities.

Chlorinator: A mechanical device specifically designed to feed chlorine gas, pellets, or solutions such as hypochlorites into a water supply in proportion to the flow of water.

Chlorine: (Cl₂) A gas widely used in the disinfection of water and as an oxidizing agent for organic matter, manganese, iron, and hydrogen sulfide. Chlorine is known to react with organic matter in the water to form trihalomethanes (THMs), a suspected carcinogen.

Chlorine Contact Chamber: That part of a water treatment plant where effluent is disinfected by chlorine.

Chlorine Demand: A measure of the amount of chlorine which will be consumed by organic matter and other oxidizable substances in a water before a chlorine residual will be found. Chlorine demand represents the difference between the total chlorine fed and the chlorine residual.

Chlorine Requirement: The amount of chlorine which is needed for a particular purpose. Some reasons for adding chlorine are reducing the number of coliform bacteria (Most Probable Number), obtaining a particular chlorine residual, or oxidizing some substance in the water. In each case, a definite dosage of chlorine will be necessary. This dosage is the chlorine requirement.

Chlorine residual: SEE residual chlorine; total chlorine residual

Chlorine, combined: SEE combined available residual chlorine

Chlorine, free: SEE free available residual chlorine

Chlorophenolic: Chlorophenolic compounds are phenolic compounds (carbolic acid) combined with chlorine.

Chlorophenoxy: A class of herbicides that may be found in domestic water supplies and cause adverse health effects. Two widely used chlorophenoxy herbicides are 2,4-D (2,4-Dichlorophenoxy acetic acid) and 2,4,5-TP (2,4,5-Trichlorophenoxy propionic acid (silvex)).

Chlororganic: Organic compounds combined with chlorine. These compounds generally originate from, or are associated with, life processes such as those of algae in water.

Chromatography: A chemical analytical technique which utilizes a process of separating gases, liquids, or solids from mixtures or solutions by selective adsorption. Chromatography involves the flow of the gas or liquid sample, which is often dissolved in a carrier solvent (termed the mobile phase), over a solid or liquid adsorbent medium (e.g., silica gel, glass beads, polystyrene gel, alumina, or ion exchange resin), which is often packed in a column and is called the stationary phase. As the mixture flows over the adsorbent medium, each substance adsorbs and desorbs through the medium at different rates, producing distinct bands that can be individually detected and identified.

Chronic: Occurring over a long period of time, either continuously or intermittently; used to describe ongoing

Chronic Exposure: The circular outer edge of a depression produced in the water table by the pumping of water from a well.

Circuit: A safety device in an electrical circuit that automatically shuts off the circuit when it becomes overloaded. The device can be manually reset.

Cistern: A small tank (usually covered) or a storage facility used to store water for a home or farm. Often used to store rainwater.

Clacium Hydroxide: Hydrated lime

Clarifier: A large circular or rectangular tank or basin in which water is held for a period of time, during which the heavier suspended solids settle to the bottom. Clarifiers are also called settling basins and sedimentation basins.

Class (pipe and fittings): The working pressure rating of a specific pipe for use in water distribution systems which includes allowances for surges. This term is used for cast iron, ductile iron, asbestos cement, and some plastic pipe.

Classification: SEE hydraulic classification

Clay: A type of naturally-occurring hydrated aluminum silicate Al₂O₃SiO₂x H₂O soil. Natural clay is activated and used as a coagulant adsorbent filter aid. Clay particles can have a diameter of less than five microns.

Clay Soil: A soil containing more than 40 percent clay, but less than 45 percent sand, and less than 40 percent silt.

Clear Well: A reservoir for the storage of filtered water of sufficient capacity to prevent the need to vary the filtration rate with variations in demand. Also used to provide chlorine contact time for disinfection.

Clear water iron: SEE ferrous iron

Clinical Studies: Studies of humans suffering from symptoms induced by chemical exposure.

Club Soda: Soda water to which additional mineral salts have been added.

Clumping: The formation of media agglomerations or resin clumps within an operating filter or ion exchange bed due to organic fouling or electrostatic charges.

Coagulant: A material, such as alum, which will form a gelatinous precipitate in water and cause the agglomeration of finely divided particles into larger particles which can then be removed by settling and/or filtration.

Coagulant Aid: A material which is not a coagulant, but which improves the effectiveness of a coagulant–often by forming heavier particles, speeding the reactions, or permitting reduced coagulant dosage. Also called a filter aid.

Coagulation: The clumping together of very fine colloidal (less than 0.1 micron in size) and dispersed (0.1 to 100 microns in size) particles into larger visible agglomerates of these particles (usually between 100 and 1,000 microns in size) caused by the use of chemicals (coagulants). The chemicals neutralize the electrical charges of the fine particles and cause destabilization of the particles. This clumping together makes it easier to separate the solids from the water by settling, skimming, draining, or filtering.

Coalescence: The union or growing together of colloidal particles into a group or larger unit as a result of molecular attraction on the surfaces of the particles.

Cocurrent flow: SEE downflow

Cohesion: Molecular attraction which holds two particles together

Cold Sterilization: The use of submicron filtration to screen out bacteria from a water or fluid.

Coliform Bacteria: A particular group of bacteria primarily found in human and animal intestines and wastes. These bacteria are widely used as indicator organisms to show the presence of such wastes in water and the possible presence of pathogenic (disease-producing) bacteria. Escherichia coli (E. coli) is one of the fecal coliform bacteria widely used for this purpose.

Collector: A device or system designed to collect backwash water from a filter or ion exchange bed. A collector may also be used as an upper distributor to spread the flow of water in downflow column operation.

Colloids: Very fine solid particles, typically between 0.1 and 0.001 microns in diameter, which are suspended in a liquid or gas and will not settle out of a solution and cannot be removed by conventional filtration alone. When in sufficient concentrations, colloidal matter may give a grayish cast to a standing water sample. The removal of colloidal particles usually requires coagulation to form larger particles which may then be removed by sedimentation and/or filtration.

Color: A shade or tint which is imparted to water by substances which are in true solution and thus cannot be removed by mechanical filtration. Color is most commonly caused by dissolved organic matter, but it may be produced by dissolved mineral matter.

Color Throw: The discharge of color into the effluent of an ion exchange or filter media system by any component. Usually occurs after an extended “standing” period which allows slowly-soluble colored matter to accumulate in the water. A color throw may result from the leaching of color bodies from an ion exchange resin into the water.

Colorimetric Measurement: A means of measuring unknown chemical concentrations in water by measuring a sample’s color intensity. The specific color of the sample, developed by addition of chemical reagents, is measured with a photoelectric colorimeter or is compared with “color standards” using, or corresponding with, known concentrations of the chemical.

Column: A vessel, usually a cylindrical and vertical tank, with an inlet at one end and an outlet at the other end, with some means of holding the medium in place so that a stream of water passing through it is processed. Also known as a bed of filter or catalyst medium, or ion exchange resin.

Column Operation: The process in which the solution to be treated is passed through a column in either an upflow or downflow pattern.

Combined Available Residual Chlorine: The concentration of residual chlorine which is combined with ammonia (NH3) and/or organic nitrogen in water as chloramine (or other chloro derivative) yet is still available to oxidize organic matter and utilize its bactericidal properties. The combined chlorine compounds are more stable than free chlorine forms, but are somewhat slower in reactions.

Combined Residual Chlorination: The application of chlorine to water to produce combined available residual chlorine. This residual can be made up of monochloramines, dichloramines, and nitrogen trichloride.

Combined Sewer: A sewer that transports surface runoff and human domestic wastes (sewage), and sometimes industrial wastes. Waste water and runoff in a combined sewer may occur in excess of the sewer capacity and cannot be treated immediately. The excess is frequently discharged directly to a receiving stream without treatment, or to a holding basin for subsequent treatment and disposal.

Commercial Water Treatment Equipment: Water treatment equipment designed for connection to the water system with conventional plumbing fittings of greater than one inch internal pipe size (IPS) and designed for commercial or light industrial uses.

Common Salt: Sodium chloride (NaCl). A white or colorless crystalline compound that occurs abundantly in nature (present as 2.6 percent of seawater) and in animal fluids. Sodium chloride is used in water treatment to regenerate cation exchange water softeners and some dealkalizer systems. Also called table salt or common table salt.

Community Water System: A public water system which serves at least 15 service connections used by year-round residents or regularly serves at least 25 year-round residents.

Compensated Hardness: A calculated value based upon the total hardness, the magnesium-to-calcium ratio, and the sodium, iron, and manganese concentrations in a water. This value is used to correct for the reduction in hardness removal capacity of a cation exchange water softener which is caused by the presence of these substances. No single method of calculation has been uniformly accurate.

Complete Treatment: In municipal water treatment, a method of treating water which consists of the addition of coagulant chemicals, flash mixing, coagulation – flocculation, sedimentation, and filtration. Also called conventional filtration.

Complexation: The inactivation of an ion by addition of a reagent that combines with it and, in effect, prevents it from participating in other reactions. Complexation is also call sequestration.

Complexes: Compounds formed by the union of two or more simple salts.

Compliance Cycle: The nine-year calendar year cycle during which public water systems must monitor for regulated drinking water contaminants. Each compliance cycle consists of three three-year compliance periods. The first calendar year cycle begins January 1, 1993 and ends December 31, 2001; the second begins January 1, 2002 and ends December 31, 2010; the third from January 1, 2011 to December 31, 2019, etc.

Compliance Period: A three-year calendar period within a compliance cycle. Each compliance cycle has three three-year compliance periods. Within the first compliance cycle, the first compliance period runs from January 1, 1993 to December 31, 1995; the second from January 1, 1996 to December 31, 1998; the third from January 1, 1999 to December 31, 2001.

Composite Membrane: A semipermeable membrane used in water treatment, consisting of a rejecting barrier layer of one chemical composition (usually a type of polymer) supported by one or more layers of porous materials with different composition(s).

Composite sample: A mixture of single or “grab”samples. A composite is intended to produce a typical or average sample when wide variations in quality or characteristics occur in the various grab samples. A composite may be made up of equal volumes of individual samples or of single samples which are proportioned to variations in flow or usage

Composting: A controlled microbial degradation of organic waste that yields an environmentally sound, nuisance-free product of potential value as a soil conditioner.

Compound: A substance composed of two or more elements whose composition is constant. For example, table salt (sodium chloride – NaCl) is a compound.

Concentrate Recycle: In reverse osmosis and electrodialysis applications, a technique for increasing the amount of product water by recycling a fraction of the concentrate stream back through the membrane or membrane stack.

Concentrate Stream: In reverse osmosis applications, the stream into which rejected ions and materials are concentrated.

Concentrated Solution: A solution which contains a relatively high quantity of the solute.

Concentration: 1. The process of increasing the dissolved solids per unit volume of solution, usually by evaporation of the liquid or separation of the liquid by passage through a semipermeable membrane.

2. The amount of the material dissolved in a unit volume of a solution.

Concentration Polarization: 1. The ratio of the salt concentration in the membrane boundary layer to the salt concentration in the bulk stream. The most common and serious problem resulting from concentration polarization is the increasing tendency for precipitation of sparingly soluble salts and the deposition of particulate matter on the membrane surface.

2. Used in corrosion studies to indicate a depletion of ions near an electrode.

3. The basis for chemical analysis by a polarograph.

Condensate: Water obtained by condensation of steam or water vapor.

Conditioned Water: Any water which has been treated by one or more processes (adsorption, deionization, filtration, softening, reverse osmosis, etc.) to improve the water’s usefulness and/or aesthetic quality by reducing undesirable substances (iron, hardness etc.) or undesirable conditions (color, taste, odor, etc.).

Conductance: A measure of the ability of a solution to allow an electric current to flow through it; the reciprocal of resistance. The unit of measure for conductance is the siemens (formerly called mho), which is the reciprocal of the ohm (the unit of measure for resistance). In electrolytic or ionic solutions, the current is carried by ions; liquids such as pure water, glass, and high polymers (such as rubber and cellulose) exhibit poor conductance.

Conductivity: The property of a substance to conduct (carry) heat or electricity; the unit of measure is the siemens (formerly called mho), which is the reciprocal of resistivity (1 divided by resistivity).

Conductor: A substance, body, device, or wire that readily conducts or carries electrical current.

Cone of Depression: The depression, roughly conical in shape, produced in the water table by the pumping of water from a well.

Cone of Influence: The depression, roughly conical in shape, produced in the water table by the pumping of water from a well.

Confined Aquifer: An aquifer in which groundwater is confined under pressure which is significantly greater than atmospheric pressure.

Confluent Growth: A continuous bacterial growth covering the entire filtration area of a membrane filter, or a portion thereof, in which bacterial colonies are not discrete.

Confounding Factors: Variables other than controlled exposure level which can affect the incidence or degree of a parameter being measured.

Connate Water: Water which was deposited, by geological means, simultaneously with the surrounding rock formations and held without flow. Usually this water occurs in the earth and is high in minerals due to long contact with the rock.

Consumptive Use: Water removed from available supplies without direct return to a water resource system for uses such as manufacturing, agriculture, and food preparation.

Contact Time: 1. The time in minutes the water is in contact with an ion exchange medium or filter medium.

2. The time the brine or other ion exchange regenerant is in intimate contact with the resin.

3. As relates to disinfection, the time the water is allowed to contain the disinfectant to assure potability. Contact time may also be called retention time.

Contactor: 1. An electrical switch, usually magnetically operated.

2. Equipment (e.g., an injector and vessel) used to promote contact and mass transfer between treatment materials and the water and other substances to be treated; hydraulic or mechanical mixing to ensure thorough distribution may be provided.

Contaminant: 1. Any undesirable physical, chemical, or microbiological substance or matter in a given water source or supply. Anything in water which is not H2O may be considered a contaminant.

2. Any foreign component present in another substance.

Contamination: The introduction of any contaminant into a water source or supply.

Contimuous Sample: A flow of water from a particular place in a plant to the location where the sample are collected for testing. This continuous stream may be used to obtain grab or composite samples. frequently, several taps (faucets) will flow continuously in the laboratory to provide test samples from various places in a water treatment plant.

Continous Flow Operation: The process wherein a continuous and steady flow of water is processed for treatment through the media (as compared to intermittent flow operation).

Contour Farming: A conservation-based method of farming in which all farming operations (for example, tillage and planting) are performed across (rather than up and down) the slope. Ideally, each crop row is planted at right angles to the ground slope.

Contour Strip Farming: A kind of contour farming in which row crops are planted in strips, between alternating strips of close-growing, erosion resistant forage (grass, grain, or hay) crops.

Control Loop: The path through the control system between the sensor, which measures a process variable, and the controller, which controls or adjusts the process variable.

Control System: A system which senses and controls its own operation on a close, continuous basis in what is called proportional (or modulating) control.

Controller: A device which controls the starting, stopping, or operation of a device or piece of equipment.

Convection: The transfer of heat through a fluid by circulating currents.

Conventional Filtration: In municipal water treatment, a method of treating water to remove particulates. The method consists of the addition of coagulant chemicals, flash mixing, coagulation – flocculation, sedimentation, and filtration. Also called complete treatment.

Conventional Filtration Treatment: In municipal water treatment, a series of processes including coagulation, flocculation, sedimentation, and filtration resulting in substantial particulate removal.

Conventional Tillage: The traditional method of farming in which soil is prepared for planting by completely inverting it with a moldboard plow. Subsequent working of the soil with other implements is usually performed to smooth the soil surface. Bare soil is exposed to the weather for some varying length of time depending on soil and climatic conditions.

Conveyance Loss: Water lost in conveyance (pipe, channel, conduit, ditch) by leakage or evaporation.

Cooling Water: 1. Water which is used to remove heat from air conditioning coils in commercial buildings. For example, by use of cascading cooling towers.

2. Water used in the condensation step of a distillation system.

Coordinated Phosphate Treatment: AKA captive alkalinity or coordinated phosphate/pH Ccntrol are chemical techniques used to prevent corrosion in boilers. The buffering action of the phosphate treatment will minimize the potential for acid and caustic based corrosion; and in conjunction with Sodium Hydroxide (NaOH) can provide the optimum pH necessary to minimize the corrosion of carbon steel, and to speed oxygen scavenger reactions. Staying within the control boundaries of phosphate and pH is key to successful operation of high-pressure industrial boilers. These boundaries are described with logarithmic control charts.

Core Sample: A sample of the medium obtained to represent the entire bed depth when the bed is being analyzed for capacity or usefulness. A hollow tube is sent down through the bed to extract the sample.

Corona: An electrical discharge effect which causes ionization of oxygen and the formation of ozone.

Corona Discharge: The discharge of electricity causing a faint glow adjacent to the surface of an electrical conductor and, similarly, adjacent to the dielectrics in an ozone generator during ozone production. Corona discharge results from electrical discharge and indicates ionization of oxygen and the formation of ozone in the surrounding air. The corona discharge is a violet-blue color with air, but colorless with high purity oxygen.

Corporation Stop: A water service shutoff valve located at a street water main. This valve cannot be operated from the ground surface because it is buried and there is no valve box. Also called a corporation cock.

Corrosion: The natural interaction between a refined metal and its environment (Physical and Chemical) which results in changes to the properties of the metal, typically creating stable oxide, hydroxide, or sulfide compounds that will result in the eventual destruction of the refined metal. Corrosion will compromise the useful properties of refined metals, including their strength, appearance, and permeability to liquids and gases.

There are many factors that contribute to corrosion, but the most common are galvanic action (dissimilar metals in direct contact, or indirect contact through an electrolyte), electrolysis (galvanic action with the addition of external current), oxidation/reduction reactions, acid/base reactions, and microbial activity.

“Corrosion” can also occur in materials other than metals, such as ceramics, composites, and polymers, where the term “degradation” is more commonly used. SEE ALSO corrosivity; stray current corrosion.

Corrosion Inhibitor: A substance that slows the rate of corrosion of metal plumbing materials by water, especially lead and copper materials, by forming a protective film on the interior surface of those materials.

Corrosion-Resistant Material: A material which resists corrosion after prolonged placement in the environment in which the material was intended to be used. Corrosion-resistant materials do not contribute unacceptable amounts of corroded material into the processed water.

Corrosivity (of water): An indication of the potential of materials to corrode under specific water conditions. The corrosivity of water can be affected by pH, Total Alkalinity, Temperature, Conductivity, Chloride/Sulfate Mass Ratio (CSMR), Dissolved gases, and Microbiological activity. SEE ALSO corrosion.

Cost Benefit Analysis: A quantitative evaluation of the costs which would be incurred versus the overall benefits to society of a proposed action such as the establishment of an acceptable dose of a toxic chemical.

Cost Sharing: A publicly financed program through which society, as the beneficiary of environment protection, shares part of the cost of pollution control with those who must actually install the controls.

Cost/benefit analysis: A quantitative evaluation of the costs which would be incurred versus the overall benefits to society of a proposed action such as the establishment of an acceptable dose of toxic chemical.

Coulomb: A measurement of the amount of electrical charge conveyed in one second by an electric current of one ampere. One coulomb equals about 6.25 X 10<sup>18</sup> electrons (6,250,000,000,000,000,000 electrons)

Coupon: A steel specimen inserted into water to measure the corrosiveness of water. The rate of corrosion is measured as the loss of weight of the coupon (in milligrams) per surface area (in square decimeters) exposed to the water per day. 10 decimeters = 1 meter = 100 centimeters.

Cover Crop: A crop that provides temporary protection for delicate seedlings and/or provides a canopy for seasonal soil protection and improvement between normal crop production periods. Except in orchards where permanent vegetative cover is maintained, cover crops usually are grown for one year or less. When plowed under and incorporated into the soil, cover crops are also referred to as green manure crops.

Crenothrix Polyspora: One of several types of bacteria which utilize iron in their metabolism and are capable of depositing gelatinous ferric hydroxide.

Critical Bed Depth: The minimum depth of an ion exchange, adsorbent, or otherwise reactive filter bed that is required to contain the mass transfer zone.

Critical Pressure: The minimum pressure necessary to liquify a gas which is at critical temperature.

Critical Temperature: The temperature above which a gas cannot be liquefied solely by an increase in pressure.

Crop Rotation: A system of farming in which a regular succession of different crops are planted on the same land area, as opposed to growing the same crop time after time (monoculture).

Cross Connection: 1. A physical connection through which the quality of processed water could be degraded.

2. The condition wherein a nonpotable (sewer) pipe line is directly piped into a potable water line, resulting in possible backflow or backsiphonage and contamination of the drinking water supply.

Cross Contamination: 1. Contamination which occurs in a mixed bed deionizer unit when anion and cation resins are mixed together after regeneration due to the malfunction of the system.

2. The intermixing of two water streams which results in unacceptable water quality for a given purpose.

Cross Leakage: Water leakage between the demineralized and the concentrate streams in the membrane stack used in the electrodialysis process.

Cross flow filtration: A type of filtration that uses the shear force of tangential flow across the membrane surface (during suspension recirculation) to keep the particle buildup to a minimum. Particle boundary layers cannot be completely eliminated by cross flow, however, due to low fluid velocity that exists at the membrane surface. Ultrafiltration and reverse osmosis are examples of cross flow filtration. Cross flow filtration is also called tangential flow filtration.

Cross-Linking: 1. A comparatively short connection composed of either an element, a chemical group, or a compound that bridges between neighboring chains of atoms in a complex chemical molecule (especially a polymer). Cross-linking is indicated in the following schematic diagram: P1 X X (DAN: LINES SHOULD BE IN HERE) P2 P1, P2 = polymer chains X = cross-linking unit Cross-linking changes a plastic from thermoplastic to thermosetting, and it increases strength, durability, heat and electrical resistance, and resistance to solvents and other chemicals. Examples are: a) vulcanization of rubber with sulfur or organic peroxides, b) cross-linking of polystyrene with divinylbenzene (see 2. in this definition), and c) cross-linking of polyethylene by means of high-energy radiation or with an organic peroxide (see cross-linked polyethylene (XLPE or PEX).

2. The bonding of linear polymers into a resinous product with a material such as divinylbenzene (DVB) producing a tridimensional exchanger product. The cross-links give the resin structure its strength, insolubility, and resistance to melting and distorting over a range of temperatures. Cross-linking also determines the tightness or porosity of the resin structure, and the degree of cross-linking is a factor of the resin’s ability to withstand chemical oxidation. Standard softening resin is usually 8 percent cross-linked with divinylbenzene or 8 percent DVB. Anion resins can be from 2 percent to 8 percent cross-linked. Acrylics can also be used instead of DVB for cross-linking.

Cross-Sectional Area: The area of a plane in a tank or vessel which is at a right angle to the direction of the flow. The cross-sectional area is expressed in square feet (ft2) and used to calculate the service flow rate or the backwash flow rate. For example: A rate of five U.S. gallons per minute per square foot (5 gpm/ft2) of ion exchange bed area.

Cross-linked Polyethylene (XLPE or PEX): Polyethylene that, by cross-linking via irradiation of linear polyethylene with an electron beam or gamma radiation, or with a chemical cross-linking agent, such as benzoyl peroxide, is made to be a non-toxic thermosetting (remains solid upon heating) white solid with superior strength and durability, high temperature and pressure resistance, and inertness toward chemical attack and corrosion. Cross-linked polyethylene pipe and tubing is accepted by many plumbing codes for potable water distribution with buildings. It is flexible (bend radii of six times or greater the outside pipe/tubing diameter) and can be used in place of polybutylene (PB) water pipe.

Cryptosporidiosis: (crip-toe-spor-ID-ee-OH-sis): The illness produced by infection with Cryptosporidium. The most common symptoms of this disease including fever, headache, nausea, vomiting, anorexia, abdominal cramping, and watery diarrhea. These symptoms usually begin two to ten days after infection and generally last two weeks or less. Cryptosporidiosis in individuals with weakened immune systems is a more severe disease. The most common symptoms of this disease including fever, headache, nausea, vomiting, anorexia, abdominal cramping, and watery diarrhea. These symptoms usually begin two to 10 days after infection and generally last two weeks or less. Cryptosporidiosis in individuals with weakened immune systems is a more severe disease.

Cryptosporidium: (crip-toe-spor-ID-ee-um) A waterbourne protozoan that forms oocysts and causes acute gastrointestinal illness in humans. Several species of cryptosporidium exist, but only one, C. parvum, is known to be infective to humans. In the environment, the organism’s fertilized eggs are protected by an outer shell form called an oocyst (OH-oh-cist). Once injested, the organism emerges from the shell and infects the lining of the small intestines. Cryptosporidium is commonly found in unfiltered surface water and is resistant to disinfectants such as chlorine and ultraviolet light, but C. parvum oocysts, generally being three to five microns in diameter, can be removed by filters that capture all particles of one micron and greater in size.

Cube: A cubic foot of cation resin or filter medium. (A term as used in the water treatment industry.)

Cubic Foot: Volume equal or equivalent to that of a cube one foot long on each side. The commonly used (in the United States) unit of volume for the measurement of the volume of ion exchangers and most loose filter media. The measurement is made on the media in an in-place condition (under conditions as if the resin were actually in-place in equipment during service) after the specific steps of backwashing, settling, and draining the excess water from the bed. The liter measurement is used in other countries.

Cumulative Exposure: The summation of exposures of an organism to a chemical over a period of time.

Curb Stop: A water service shutoff valve located in a water service pipe near the curb and between the water main and the building. This valve is usually operated by a wrench or valve key and is used to start or stop flows in the water service line to a building. Also called a “curb cock.”

Curie (Ci): The term used to describe the rate of radioactive decay. A curie = 3.7 X 10E+10 disintegrations per second, and a curie = 3.7 X 10E+10 becquerels (Bqs).

Current: A movement or flow of electricity. Water flowing in a pipe is measured in gallons per second past a certain point, not by the number of water molecules going past a point. Electric current is measured by the number of coulombs per second flowing past a certain point in a conductor. A coulomb is equal to about 6.25 X 10E+18 electrons (6,250,000,000,000,000,000 electrons). A flow of one coulomb per second is called one ampere, the unit of the rate of flow of current.

Cyanobacteria: Single-celled organisms (singular = cyanobacterium) similar to bacteria, except cyanobacteria contain the green pigment chlorophyll (as well as other pigments), which traps the energy of sunlight and enables these organisms to carry on photosynthesis. Cyanobacteria are autotrophic producers of their own food from simple raw materials, whereas bacteria are heterotrophic decomposers of the wastes and bodies of other organisms. Cyanobacteria were formerly known as blue-green algae. Blooms or population explosions of cyanobacteria cause water pollution. Some cyanobacteria-like bodies (CLBs) have been associated with causing waterborne diarrheal illnesses.

Cyanobacteria-like Bodies (CLBs): Organisms that, upon analysis, appear to be cyanobacteria i.e., 8-10 micrometers in size, staining red with modified acid-fast stains, and autofluorescing under ultraviolet (UV) light. Cyclospora oocysts have been sometimes confused for cyanobacteria-like bodies in microorganism analyses.

Cyanosis: A dusky bluish or purplish discoloration of the skin or mucous membranes due to insufficient oxygen in the blood as could be caused by excessive nitrates in drinking water and methemoglobinemia in infants.

Cycle: A series of steps which ultimately lead back to the starting point, such as the exhaustion-regeneration cycle of an ion exchange system or the service run, backwash, and rinse steps of the filtration process. The word “cycle” is sometimes incorrectly used to refer to a single step of a complete cycle.

Cycle of Concentration: A cycle related to the changing ratio of solids and water volume in any vessel from which water evaporates, such as a still, a swimming pool, a steam boiler, or a cooling tower. As the water evaporates, the formerly dissolved solids remain behind. The new water which is added (to replace the evaporated water) also contains dissolved solids, so the concentration ratio of solids to water increases proportionately. For example: assume a boiler system holds a total 1,000 gallons of water. When the first 1,000 gallons evaporates, the solids are left behind. Then an additional 1,000 gallons of makeup water is added (to replace the evaporated water) and the makeup water also contains a quantity of solids. The system still holds only 1,000 gallons but the amount of solids has now doubled and the system now holds two concentrations of solids. The concentration is now two (solids) to one (volume of water). If 3,000 gallons of makeup water are added, the concentration becomes four (solids) to one (volume of water). These calculations of concentration ratios are used to determine when blowdown is needed in boiler or cooling tower operation.

Cyclospora: A genus of protozoa parasites belonging to the order Coccidia and the phylum Apicomplexa. Cyclospora cayetanensis species are pathogenic to humans causing disease symptoms similar to those caused by Cryptosporidium, except cyclosporiasis does appear responsive to treatment with medicine such as trimethoprim-sulfamethoxazole (TMP-SMX). Cyclospora reproduce with environmentally resistant oocysts (about 8-10 micrometers in size) that can be carried viably in unfiltered water supplies.

Cyst: A capsule or protective sac produced about themselves by many protozoans (as well as some bacteria and algae) as preparation for entering a resting or a specialized reproductive stage. Similar to spores, cysts tend to be more resistant to destruction by disinfection. Fortunately, protozoan cysts are typically 2 to 50 microns in diameter and can be removed from water by fine filtration.

cfu: colony-forming units

coliform organism: See colloids

DIC: Dissolved Inorganic Carbon.

DIC: Dissolved Inorganic Carbon.

DIR: Demand Initiated Regeneration.

DOC: Dissolved Organic Carbon.

DPD: A method of measuring the chlorine residual in water. The residual may be determined by either titrating or comparing a developed color with color standards. DPD stands for N,N-diethyl-p-phenylene-diamine.

DVB: Divinylbenzene.

DWEL: Estimated exposure (in mg/L) which is interpreted to be protective for noncarcinogenic endpoints of toxicity over a lifetime of exposure. DWEL was developed for chamicals that have a significant carcinogenic potential (Group B). Provides risk manager with evaluation on noncancer endpoints, but infers that carcinogenicity should be considered the toxic effect of greatest concern.

Dateometer: A small calendar disc attached to motors and equipment to indicate the year in which the last maintenance service was performed.

Dateometer: A small calendar disc attached to motors and equipment to indicate the year in which the last maintenance service was performed.

Day Tank: 1. A tank used to hold diluted regenerant chemicals prior to being pumped into a batch regeneration of ion exchange beds. Day tanks are commonly used in exchange tank regeneration operations.

2. A tank used to store a chemical solution of known concentration for feed to a chemical feeder. A day tank usually stores sufficient chemical solution to properly treat the water being treated for at least one day. Also called an age tank.

Dead End: The end of a water main which is not connected to other parts of the distribution system by means of a connecting loop of pipe.

Dead End Filtration: A flow pattern in which all water flows through the medium or membrane (as opposed to cross flow filtration) thus allowing a buildup of a particulate layer on or near the surface of the medium and requiring periodic backwashing, repeated cleaning, or cartridge replacement.

Dealkalization: The dealkalization of water refers to the removal of alkalinity ions from the feed stream. This is readily done with chloride cycle anion exchange whereby the alkalinity (bicarbonate or carbonate) is removed in exchange for chloride. The resin can be regenerated with salt (NaCl).
In a boiler, alkalinity decomposes under heat to produce CO₂ so the steam that is produced contains carbonic acid (H₂CO₃) and can be highly corrosive. Dealkalization avoids this. In addition, the removal of alkalinity avoids the formation of boiler scale (CaCO₃) because the chloride salt of calcium is very soluble and does not form deposits. SEE ALSO anion softening.

Decant: To draw off the upper layer of liquid (water) after the heavier material (a solid or another liquid) has settled.

Decantation: The process of drawing off a supernatant liquor without disturbing the underlying lower liquid layers and the precipitate.

Decationize: The exchange of cations for hydrogen ions by a strong acid cation exchanger operated in the hydrogen form.

Dechlorination: The deliberate removal of chlorine from water. The partial or complete reduction of residual chlorine by any chemical or physical process.

Decibel: A unit for expressing the relative intensity of sounds on a scale from zero for the average least perceptible sound to about 130 for the average level at which sound causes pain to humans.

Decolorization: The process of removing color bodies such as tannins or humic acid from water by means of oxidation, coagulation/filtration, adsorption, or ion exchange.

Decomposition: The conversion of chemically unstable materials to more stable forms by chemical or biological action. If organic matter decays when there is no oxygen present (anaerobic conditions or putrefaction), undesirable tastes and odors are produced. Decay of organic matter when oxygen is present (aerobic conditions) tends to produce much less objectionable tastes and odors.

Decross-Linking: The alteration of an ion exchange resin structure by destruction of the cross-link polymer (such as divinylbenzene) as the result of very aggressive chemical attack (by chlorine, ozone or hydrogen peroxide, for example) or heat. Decross-linking causes increased moisture content in an ion exchange resin and the physical swelling of the beads.

Defluoridation: The removal of excess fluoride in drinking water to prevent the mottling (brown stains) of teeth.

Degassing, Degasify, Degasification: The removal of dissolved gases such as carbon dioxide, methane, hydrogen sulfide, and oxygen by:
1. subjecting the water to a pressure below atmospheric pressure (vacuum degassing) or

2. passing large amounts of air thoroughly through the water at atmospheric pressure (air stripping).

Degradation: As relates to ion exchange, the loss of capacity, reduction of resin particle size, excessive swelling of resin particles, or any combination of these factors resulting in a lessening of the ion exchange capabilities of the resin. This may occur as a result of the type of service for which the resin was used, the solution concentrations used, heat, or aggressive operating conditions.

Deionization: The removal of all ionized minerals and salts (both organic and inorganic) from a solution by a two-phase ion exchange procedure: First, positively-charged ions are removed by a cation exchange resin in exchange for a chemically equivalent amount of hydrogen ions. Second, negatively-charged ions are removed by an anion exchange resin for a chemically equivalent amount of hydroxide ions. The hydrogen and hydroxide ions introduced in this process unite to form water molecules. This process is also called demineralization by ion exchange.

Delivered Water: The finished product water from a public or private utility water plant which is carried through a water main network of pipes and arrives at the point-of-use (homes, institutions, and business facilities).

Delta P: The pressure drop or loss (in psi) by flowing water in a pressurized system as the result of the velocity and turbulence of the flowing water, restrictions the water flows through, and roughness of surfaces the water flows past. The symbol for Delta P is P.

Demand Initiated Regeneration (DIR): A method of automatically initiating regeneration or recycling in filters, deionizers, or softeners after a pre-determined metered volume of water has been processed. In a softener or deionizer, regeneration may be triggered automatically based upon an electrical or mechanical signal. All operations including bypass (of hard or soft water depending upon design), backwashing, brining, rinsing, and returning the unit to service are initiated and performed automatically in response to the demand for treated water.

Demineralization by Ion Exchange: See deionization.

Denitrification: The biochemical conversion of nitrate and nitrite nitrogen in the soil dissolved in water to gaseous nitrogen.

Density: The mass of a substance per specified unit of volume; for example, pounds per cubic foot. True density is the mass per unit volume excluding pores; apparent density is the mass per unit volume including pores. The density of water is 1.0 gram per cubic centimeter or about 62.4 pounds per cubic foot.

Deposits: See Water Spotting.

Depth Filter: Depth (deep bed) filters use a tortuous path to entrap particles deep within the body of the filtration media. A tortuous path is used in depth filters to effect rejection of solids smaller than the void spaces in the filtration media. The path enables electrostatic and intermolecular forces between the solids, causing them to clump together, adhere to the media, or form a bridge between voids that blocks the passage of additional particles. Particles are deposited in the upper part of the bed first, but once a layer of particles is deposited, additional particles simply flow past them to find a spot deeper in the bed. This is possible because the passage through the irregular maze of channels or paths in a granular bed is larger than the particles to be removed. Some of the particles are strained out; others are attracted to the medium because of electrostatic and intermolecular forces (Figure 1 C). Depth filtration can be single medium (sand) Figure 1C, or several different media Figure 1 D—either in stratified layers or mixed format.

Depth Filtration: A filtration process in which water flows through progressively smaller pore spaces in a filter media bed. Depth filters are designed to entrap particles throughout the mass of filter media, as opposed to a surface filter where only the surface layer does the actual filtering. Depth filtration can be accomplished with a multilayered bed or multimedia filtration. String-wound fiber cartridge elements can also function as depth filters.

Dermal Exposure: Contact between a chemical and the skin.

Desalination: The removal of dissolved inorganic solids (salts) from a solution such as water to produce a liquid which is free of dissolved salts. Desalination is typically accomplished by distillation, reverse osmosis, or electrodialysis.

Desiccant: [DES-uh-kant] A hygroscopic substance such as activated alumina, calcium chloride, silica gel, or zinc chloride that draws water vapor from the air. Desiccants are used to maintain a dry environment for equipment and materials.

Desiliconization: An ion exchange process designed for reduction of silica from a water supply. Typically a strong base anion exchanger operated in OH^– form is used.

Desorption: The opposite of adsorption. The process of removing an adsorbed material from the medium or resin on which it has been adsorbed. Desorption is usually accomplished by heating, a reduction of pressure, by the presence of another more strongly adsorbed substance, or a combination of these means.

Dessication: A process used to thoroughly dry air; to remove virtually all moisture from air.

Dessicator: A closed container into which heated weighing or drying dishes are placed to cool in a dry environment. The dishes may be empty or they may contain a sample. Desiccators contain a substance, such as anhydrous calcium chloride, which absorbs moisture and keeps the relative humidity near zero so that the dish or sample will not gain weight from absorbed moisture.

Destratification: The development of vertical mining within a lake or reservoir to eliminate (either totally or partially) separate layers of temperature, plant, or animal life. This vertical mixing can be caused by mechanical means (pump) or through the use of forced air diffusers which release air into the lower layers of the reservoir.

Desulfovibrio: A sulfate-reducing bacteria in water which can convert sulfates and elemental sulfur to sulfide, thereby creating hydrogen sulfide gas and the concomitant “rotten egg” odor in water supplies.

Detention Lag: The time period between the moment a change is made and the moment when such a change is finally sensed by the associated measuring instrument.

Detention Time: 1. The theoretical (calculated) time required for a small amount of water to pass through a tank at a given rate of flow.
2. The actual time in hours, minutes, or seconds that a small amount of water is in a settling basin, flocculating basin, or rapid-mix chamber. In storage reservoirs, detention time is the length of time entering water will be held before being drafted for use (several weeks to years, several months being typical). Detention Time (hr) = Basin Volume (gal.)(24 hr/day)/Flow (gal/day)

Detergent: Any material with cleansing powers: soaps, synthetic detergents, man-made alkaline materials, solvents, and abrasives. In common domestic usage, the term is often used to refer to synthetic detergents.

Dew Point: The temperature to which air must be cooled to cause condensation of the water vapor it contains.

Dewater: 1. To remove or separate a portion of the water present in a sludge or slurry. To dry sludge so it can be handled and disposed.
2. To remove or drain the water from a tank or a trench.

Dezincification: A corrosion process that removes zinc from brass but leaves the copper in place; the brass (valve or fitting) retains its original dimensions but is severely weakened and is prone to structural failure, leaks, or seepage through the body walls. Occurs most readily in waters with high chlorides and pH greater than eight.

Dialysis: The separation of components of a solution by diffusion through a semipermeable membrane which is capable of passing certain ions or molecules while rejecting others.

Diaphragm Pump: A positive-displacement pump in which the reciprocating piston is separated from the solution by a flexible diaphragm, thus protecting the piston from corrosion and erosion and avoiding related problems with packing and seals.

Diatom: A type of microscopic algae with cell walls that contain silica.

Diatomaceous Earth: A fine, siliceous (made of silica) “earth” composed mainly of the skeletal remains of diatoms, a type of free-floating, microscopic plant found in the ocean. Diatomaceous earth is used as a water filtration medium.

Diatomaceous Earth Filtration: A filtration method resulting in substantial particulate removal, that uses a process in which:
1. A “precoat” cake of diatomaceous earth filter media is deposited on a support membrane (septum); and
2. While the water if filtered by passing through the cake of the septum, additional filter media, known as “body feed,” is continuously added to the feedwater to maintain the permeability of the filter cake.

Diatomic Molecule: A molecule containing only two atoms, such as hydrogen as H₂or oxygen as O₂.

Dielectric Fitting: A plumbing fitting made of an electrical nonconductor (such as plastic) used to control galvanic corrosion when joining pipes of dissimilar metals (such as copper and galvanized steel). If the dielectric fitting is used in a main water line, a bypass strap may be necessary to maintain the continuity of existing electrical grounding since the household water pipes may have been used to ground the household electrical lines.

Differential Pressure: The difference in pressures at two points in a water system. Differences may be due to variations in elevation, or to friction losses, or to pressure drops caused by resistance to water flow through pipes, softeners, filters, or other devices.

Diffuser: See Distributor.

Diffusion: The movement of suspended or dissolved particles from a more concentrated to a less concentrated region as a result of the random movement of individual particles; the process tends to distribute them uniformly throughout the available volume.

Diffusion Feeder: A chemical feed system in which chemicals are added to a water stream in controlled quantities for pipe line or metal surface protection and/or disinfection methods. A diffusion feeder is designed in such a way that a small stream of water is diverted through a tank so that the water flows over the chemical material (or solution), a small amount of which is diffused (dissolved) into the water and carried back to the main water line. A diffusion feeder is also called a bypass feeder.

Digestion: The process by which complex organic materials are broken down and decomposed into simpler substances as a result of a chemical or biological reaction or a combination of reactions. Aerobic digestion takes place in the presence of air; anaerobic digestion takes place in the absence of air.

Digital Readout: Use of numbers to indicate the value or measurement of a variable. The readout of an instrument by a direct, numerical reading or the measured value.

Dihydrogen Oxide: Water (H₂O).

Dilute Solution: A solution that has been made weaker, usually by the addition of water.

Dilution: The act of adding more solvent or water to a given solution to make it less concentrated. Sometimes this is done to attain the proper concentration; sometimes to make the solution easier to handle.

Dimictic: Lakes and reservoirs which freeze over and normally go through two stratification and two mixing cycles within a year.

Direct Current (DC): Electrical current flowing in one direction only and essentially free from pulsation.

Direct Filtration: A filtration method of treating water which consists of the addition of coagulant chemicals, flash mixing, coagulation, minimal flocculation, and filtration. The flocculation facilities may be omitted, but the physical/chemical reactions will occur to some extent. The sedimentation process is omitted.

Direct Runoff: Water that flows over the ground surface or through the ground directly into streams, rivers, or lakes.

Discharge Head: The pressure (in pounds per square inch or psi) measured at the center line of a pump discharge and very closely to the discharge flange, converted into feet.

Disinfect: To free from infection by either a chemical or physical means; causing the absence of pathogenic or indicator coliform bacteria in drinking water. Disinfectants kill or inactivate 99.9 to 99.9999 percent (but not 100%) of microorganisms under controlled conditions. Some common disinfectants are the halogens: chlorine, iodine, bromine, and hypochlorites; ozone, potassium permanganate, hydrogen peroxide, peracetic acid; formaldehyde, glutaraldehyde, phenol (carbolic acid), organic acids, benzoic and salicylic acids and their sodium salts, high pH, heat, ionizing radiation, and electromagnetic waves such as those of ultraviolet light. The USEPA requires that a disinfection claim must show killing or inactivation of all vegetative microbes in 10 minutes.

Disinfection: The treatment of water to inactivate, destroy, and/or remove pathogenic (disease-producing) bacteria, viruses, cysts, and other microorganisms (but not completely eliminating all microorganisms) for the purpose of making the water microbiologically safe for human consumption. A disinfection operation should reduce the total viable microorganism population by 99.9 to 99.9999 percent. Disinfection may involve the use of disinfecting chemicals such as chlorine, iodine, ozone, or hydrogen peroxide; or it may involve physical processes such as distillation, microfiltration, ultrafiltration, boiling, or ultraviolet radiation.

Disinfection Byproduct: A compound formed by the reaction of a disinfectant such as chlorine with organic material in the water supply.

Dispersant: A chemical (such as a polyphosphate) added to water which causes particulates in water to remain in suspension.

Dispersing Agent: A material that increases the stability of particles in a liquid.

Disposable Component: Any component of a piece of water treatment equipment or water treatment system which is manufactured to be disposed of instead of repaired or reused. Example: A cartridge filter element.

Dissociation: The process by which a chemical combination breaks up into simpler constituents such as atoms, groups of atoms, ions, or multiple different molecules. Often this breakdown is reversible, as in the case of ionization.

Dissolved Inorganic Carbon: 1. The fraction of inorganic carbon (the carbonate, bicarbonate, and dissolved CO₂) in water that passes through a 0.45 micron pore-diameter filter.
2. A calculated estimate of the concentrations of carbonate alkalinity present in water as carbon dioxide gas, (CO₂ ), bicarbonate (HCO₃^– ), and carbonate (CO₃^2-). The calculation is based on the pH and alkalinity measurements. The result is expressed as mg of carbon per liter, mg C/L

Dissolved Matter: That portion of matter or solids, exclusive of gases, which is dispersed in water to produce a homogenous liquid. According to the definition used in the water treatment industry, “dissolved matter” is that portion of the total matter that will pass through a 0.45-micron pore-diameter membrane filter.

Dissolved Organic Carbon: The fraction of total organic carbon (all carbon atoms covalently bonded in organic molecules) in water that passes through a 0.45-micron pore-diameter filter.

Dissolved Oxygen: Measure of water quality indicating free oxygen dissolved in water.

Dissolved Solids: The weight of matter, including both organic and inorganic matter, in true solution in a stated volume of water. The amount of dissolved solids is usually determined by filtering water through a 0.45 pore-diameter micron filter and weighing the filtrate residue left after the evaporation of the water at 180 degrees Celsius.

Distillate: The product water or condensate, which is mineral-free and potable, from a distiller unit.

Distillation: The process of separating the water from the organic and inorganic contaminants through a combination of evaporation (or vaporization), cooling, and condensation.

Distilled Water: Water which has been cleansed by passing through one or more evaporation-condensation cycles until it contains a very low amount of dissolved solids (usually less than 5.0 ppm TDS).

Distributor: A fitting, usually installed at the top and bottom of the tank in a loose media system, which is designed to produce even flow through all sections of an ion exchanger or filter media bed and to function as a retainer of the media in the tank. May also be called a diffuser.

Divalent: [die-VAY-lent] Having a valence of two, such as the ferrous ion, Fe²⁺. Also called bivalent.

Diversion: 1. Use of part of a stream flow as a water supply.
2. A structural conveyance (or ditch) constructed across a slope to intercept runoff flowing down a hillside, and diverting it to some convenient discharge point.

Divinylbenzene (DVB): A polymerization monomer used as a cross-linking agent by polymerization with styrene in the manufacture of many synthetic ion exchange resin products. The degree of DVB cross-linkage is a factor in exchanger resistance to chemical oxidation. Standard cation resin usually contains about 8% DVB. Macroporous resins contain over 12% DVB cross-linking.

Dolomite: [CaMg(CO₃)₂] A carbonate mineral of calcium and magnesium found in nature in extensive beds of compact limestone and marble that are rich in magnesium carbonate.

Domestic or Other Nondistribution System Plumbing Problem: A coliform contamination problem in a public water system with more than one service connection that is limited to the specific service connection from which the coliform positive sample was taken.

Dosage: The quantity of a chemical administered to an organism.

Dose: The actual quantity of a chemical to which an organism is exposed.

Dose Equivalent: The product of the absorbed dose from ionizing radiation and such factors as account for differences in biological effectiveness due to the type of radiation and its distribution in the body as specified by the International Commission on Radiological Units and Measurements (ICRU).

Dose-Response: A quantitative relationship between the dose of a chemical and an effect caused by the chemical.

Dose-Response Curve: A graphical presentation of the relationship between degree of exposure to a chemical (dose) and observed biological effect or response.

Dose-Response Evaluation: A component of risk assessment that describes the quantitative relationship between the amount of exposure to a substance and the extent of toxic injury or disease.

Dose-Response Relationship: The quantitative relationship between the amount of exposure to a substance and the extent of toxic injury produced.

Down Gradients: The direction that groundwater flows; similar in concept to downstream for surface water, such as down river.

Downflow: The term used to designate the direction (downward) in which water or a regenerant flows through an ion exchange or filter media bed during any phase of the operating cycle. This is the flow pattern found in conventional column operation: in at the top, out at the bottom of the column. The pattern may also be called cocurrent flow in ion exchange systems.

Downflow Softening: The softening process in which raw water enters at the top of the softener bed column and passes downward through the cation resin and out the bottom. In this process, the brining would also be in this same cocurrent direction.

Draft: 1. The act of drawing or removing water from a tank or reservoir.
2. The water which is drawn or removed from a tank or reservoir.

Drain: A pipe, conduit, or receptacle in a building which carries liquids by gravity to waste. The term is sometimes limited to refer to disposal of liquids other than sewage.

Drain Line: A pipeline which is used to carry backwash water, regeneration wastes, and/or rinse water from a water treatment system to a drainage receptacle or waste system.

Drainage: A technique to improve the productivity of some agricultural land by removing excess water from the soil; surface drainage is accomplished with open ditches; subsurface drainage uses porous conduits (drain tile) buried beneath the soil surface.

Drainage Basin: The area of land that drains water, sediment, and dissolved materials to a common outlet at some point along a stream channel.

Drawdown: 1. The drop in the water table or level of water in the ground when water is being pumped from a well.
2. The amount of water used from a tank or reservoir.
3. The drop in the water level of a tank or reservoir.

Drift (cooling water treatment): The loss of water that is entrained in the stack discharge.

Drilled Well: A well constructed by either cable tool or rotary methods which operates by cutting or abrasion; materials are brought to the surface by means of a hollow drill tool, a boiler, a sand pump, or by another hydraulic and/or self-cleaning method.

Drinking Water: 1. A water, treated or untreated, which is intended for human use and consumption and considered to be free of harmful chemicals and disease-causing bacteria, cysts, viruses, or other microorganisms.
2. Safe water that has been further treated to enhance aesthetic quality and/or reduce mineral content by one or more point-of-use processing devices.

Drinking Water Standards: Standards that define allowable water quality limits for potable and domestic water supplies. The U.S. Environmental Protection Agency (EPA) is responsible for the National Primary Drinking Water Regulations, which are health-related standards that establish the Maximum Contaminant Levels (MCLs) for regulated substances in drinking water. An MCL is the highest permissible level of a contaminant allowed in water delivered to the consumer’s tap. MCLs are enforceable at public water systems under the Safe Drinking Water Act. The EPA also has set Maximum Contaminant Level Goals (MCLGs) at levels which no known or anticipated adverse effects on the health of persons occur and which allow an adequate margin of safety. The enforceable MCL is set as close to the MCLG as reasonable, taking into consideration the costs and treatment techniques available to public water systems. National Secondary Drinking Water Regulations, also issued by the EPA, pertain to aesthetic characteristics of water and are advised, but not enforceable, by the Federal government.

Driven Well: A shallow, usually small well (having a diameter of 1.5 inches to 3 inches or 4 to 10 cm) constructed without the aid of any drilling, boring, or jetting device, by driving a series of connected pipe lengths into unconsolidated material to a water-bearing stratum.

Dry-Salt Saturator Tank: A brine tank, usually full of undissolved salt and with saturated brine below the undissolved salt. This is the type of brine tank used with most automatically-regenerated home softeners because it reduces the frequency of refilling the tank with salt.

Dual Chamber: A water processing system composed of two separate tanks (or compartments) vertically connected, one above the other and operated by one common set of (master) valve controls. Example: filter (top) and softening unit below (bottom).

Dual-Function Media: Any filter or ion exchange media which is used to perform two treatment steps in an application. Example: activated carbon filtration and adsorption; or cation resin softening and dissolved iron removal.

Dug Well: A shallow, large diameter well constructed by excavating with power machinery or hand tools instead of drilling or driving. Typically a dug well is constructed for an individual residential water supply and yields considerably less than 100 U.S. gallons per minute (380 L/min.)

Dynamic Pressure: When a pump is operating, the vertical distance (in feet) from a reference point (such as a pump center line) to the hydraulic grade line is the dynamic head.

Dynamic Reaction: An ion exchange reaction which takes place as the water moves past the exchange resin or resins.

Dynamic System: A process or system in which motion occurs as compared to static conditions with no motion. For example: an ion exchange system is considered a dynamic system because the continuous flow of the water to be treated creates continuous motion, as opposed to a static batch system in which the water does not move during the reaction process.

Dynamic Water Pressure: The water pressure at the inlet to a dynamic water processing system.

EDTA: See Ethylene Diamine Tetraacetic Acid.

EPA: See USEPA

Ecosystem: A system made up of the community of living things (animals, plants, and microorganisms) which are interrelated to each other and the physical and chemical environment in which they live.

Eddy: A circular movement or whirlpool occurring in flowing water due to currents created by various obstructions or dynamic forces in the water.

Education: The process of bringing something out, sucking it out, or separating it out from something else, as in drawing soda pop out of a can with a straw.

Eductor: A venturi with an opening at the throat which will educt (suck in) air or liquid. Eduction is accomplished by joining the fluids just after the constriction in the tube where a vacuum is created, thus sucking the incoming fluid into the flowing water stream. This device is commonly used to introduce (through both eduction and ejection) a gas or liquid into a flowing stream. For example, when feeding a chemical to a water supply, the venturi serves to educt the chemical from its solution container and to eject it into the water stream. Also called an ejector.

Effective Corrosion Inhibitor Residual: A concentration of corrosion inhibitor sufficient to form a protective coating on the interior walls of a pipe, reducing its corrosion.

Effective Range: That portion of the design range (usually upper 90 percent) in which an instrument has acceptable accuracy.

Effective Size: A measure of the diameter of particles in a media bed or resin bed. Effective size is that mesh size which will permit 10 percent of the bed’s particles to pass and will retain the remaining 90 percent; in other words, that size for which 10 percent of the media grains or particles are smaller and 90 percent are larger.

Efficiency: As relates to ion exchange, a measure of the effectiveness of the operational performance of an ion exchanger, usually based on the ratio of output per unit of input. This ratio is often expressed as the amount of regenerant required to produce a unit of contaminant reduction capacity. For example: pounds of salt per kilograins of hardness removed or pounds of acid per kilogram of salt removed. SEE A:LSO salt efficiency. In media filtration, efficiency is the percent of contaminant reduction which occurs with a specified medium volume and specified water contact time. In membrane filtration, the figure obtained (expressed as a percent) by dividing the volume (gallons or liters) of product water produced by the total volume (gallons or liters) of feedwater fed to the particular unit or system.

Effluent: The outflow from any water processing system or device. Sometimes used to mean the product water of a given device or system.

Ejection: The process of forcing something out, expelling it.

Ejector: A device used to disperse a chemical solution into water being treated.

Ejector Pump: A shallow or deep well pump operating on the venturi principle. Commonly referred to as a jet pump.

Electric Timer (Time Clock): An electric control device which initiates regeneration of an automatic water softener or the recycle phase of a filter unit.

Electrical Conductivity: The property of a substance to conduct (carry) heat or electricity; the unit of measure is the siemens (formerly called mho), which is the reciprocal of resistivity (1 divided by resistivity).

Electrochemical Reaction: Chemical changes produced by electricity (electrolysis) or the production of electricity by chemical changes (galvanic action). In corrosion, a chemical reaction is accompanied by the flow of electrons through a metallic path. The electron flow may come from an external force and cause the reaction, such as electrolysis caused by a DC (direct current) electric railway or the electron flow may be caused by a chemical reaction as in the galvanic action of a flashlight dry cell.

Electrochemical Series: A list of metals with the standard electrode potentials given in volts. The size and sign of the electrode potential indicates how easily these elements will take on or give up electrons, or corrode. Hydrogen is conventionally assigned a value of zero.

Electrode: A conductive, usually metallic, substance used to establish electrical contact with nonmetallic parts of a circuit.

Electrodialysis: A dialysis process using semipermeable membranes in which ions migrate through the membranes from a less concentrated to a more concentrated solution as a result of the ions’ respective attractions to a positive electrode (anode) and a negative electrode (cathode) created by direct electric current.

Electrokinetic Potential: See Zeta Potential.

Electrolysis: The decomposition of material by an outside elecrical current.

Electrolyte: 1. A substance which when dissolved in water separates into two or more ions which can carry an electric current.
2. A nonmetallic substance which can carry an electric current by movement of ions instead of electrons.

Electrolytic Cell: A device in which the chemical decomposition of material causes an electric current to flow. Also, a device in which a chemical reaction occurs as a result of the flow of electric current. Chlorine and caustic (NaOH) are made from salt (NaCl) in electrolytic cells.

Electromotive Force (EMF): The electrical pressure available to cause a flow of current (amperage) when an electrical circuit is closed.

Electromotive Series: A list of metals and alloys presented in the order of their tendency to corrode (or go into solution). Also called the Galvanic Series. This is a practical application of the theoretical electrochemical series.

Electron: A negatively-charged particle that revolves around the nucleus of an atom. In a neutral (without electrical charge) atom, the negative charges of the electrons are balanced by the positive charges of the protons in the nucleus. When an atom loses or gains one or more electrons, resulting in the atom carrying a negative or positive charge, the atom has become an ion.

Element: A substance that consists of only one kind of atom and which cannot be decomposed into simpler substances by ordinary chemical means. Examples: iron, calcium, carbon, magnesium. There are more than 100 elements, some found in nature, some man-made. Several elements may combine into more chemically complex substances such as compounds.

Elution: The process of separating or washing out adsorbed material, especially by use of a solvent. In ion exchange, the stripping of ions from the medium by passing a more highly concentrated ionized solution through the ion exchanger bed.

Emission Spectroscopy: A chemical analytical technique used to determine metal elements in water by measuring the well-defined characteristic radiation given off by each respective element as the thermally-excited element returns from an atomic vapor state to its fundamental state.

Emollient: An ingredient for making skin soft or supple, or soothing the skin. Materials such as fatty acids and lanolin are included in some toilet bars and skin preparation products to provide emollient properties.

Emulsification: The dispersion or suspension of fine particles or globules of one or more liquids in another liquid. The emulsification process is important in all types of cleaning where oily or fatty soils are encountered. The principal agent in emulsification is the surfactant, with aid from a builder that ties up hardness minerals.

End Bells: Devices used to hold the rotor and stator of a motor in position.

Endangerment Assessment: A site-specific risk assessment of the actual or potential danger to human health or welfare and the environment from the release of hazardous substances or waste. The endangerment assessment document is prepared in support of enforcement actions under U.S. environmental laws such as CERCLA or RCRA.

Endemic: Something peculiar to a particular people or locality, such as a disease which is always present in the population.

Endocarditis: Infection of the heart valves.

Endothermic: A term used to describe a process or change in which heat is absorbed and that requires high temperature for the initiation and maintenance. For example, melting ice absorbs heat and is, therefore, an endothermic process.

Endotoxin: A heat-resistant pyrogen (specifically a lipopolysaccharide) found in the cell walls of certain disease-producing bacteria.

Endpoint: The point at which a process or cycle is completed because a predetermined measurable value has been reached. Example: When the hardness in the product water reaches a set endpoint showing excessive hardness leakage, the resin bed is considered to be exhausted and in need of regeneration; when a certain predetermined color endpoint is reached during chemical titration, the process is complete.

Endrin: A pesticide toxic to freshwater and marine aquatic life that produces adverse health effects in domestic water supplies.

Energy Grade Line (EGL): A line that represents the elevation of energy head of water flowing in a pipe, conduit, or channel. The line is drawn above the hydraulic grade line (gradient) a distance equal to the velocity head of the water flowing at each section or point along the pipe or channel.

Enteric: Of intestinal origin, especially applied to wastes or bacteria.

Entrain: To trap bubbles in water either mechanically through turbulence or chemically through a reaction.

Entrainment: The process of fine droplets of liquid vapor being physically carried along or carried over by steam during distillation or evaporation. In boiler operation this is called carryover; in cooling water processes it is called drift.

Entropy: The capacity of a system or a body to hold energy that is not available for changing the temperature of the system (or body) or for doing work.

Enzymes: A large class of complex proteinaceous molecules, which act as catalysts in biochemical reactions, and as produced by living cells can bring about digestion (breakdown) of organic molecules into smaller units that can be used by living cells. Selected types of enzymes are useful in laundering, particularly in presoaking, where they break down certain soils and stains to simpler forms, which are then more readily and completely removed by the laundry soap or detergent. Reasons for their primary use in presoaking are: they need more than the usual wash period of 10-15 minutes to be effective, especially on stubborn stains and soil; also, their effectiveness is deactivated by liquid chlorine bleach, so the two must be used separately to obtain the full benefit of each.

Epidemic: Widespread outbreak of a disease, or a large number of cases of a disease, in a single community or relatively small area. Disease may spread from person to person, and/or by the exposure of many persons to a single source, such as a water supply.

Epidemiologic Study: Study of human populations to identify causes of disease. Such studies often compare the health status of a group of persons who have been exposed to a suspect agent with that of a comparable non-exposed group.

Epidemiology: A branch of medicine which studies epidemics (diseases which affect significant number of people during the same time period in the same locality). The objective of epidemiology is to determine the factors that cause epidemic diseases and how to prevent them.

Epilimnion: The topmost and warmest layer of water in an unfrozen lake. The epilimnion also contains the most oxygen of any part of the lake.

Equalization: A means of providing more uniform flow rate and composition of a water supply by use of a reservoir that receives water from a pump or treatment system, evens out the incoming flow variation, and permits temporary water withdrawal in excess of the pump or treatment system capacity.

Equilibrium: In chemistry, a condition in which reversible chemical reactions are taking place at the same time in such a manner (equivalent rate) that there is no change in the net concentration of the substances involved in the chemical processes. As a result of these simultaneous reactions, the substances involved in the reactions can be shown to be in a constant ratio to each other. In physics, the state in which the action of multiple forces produces a steady balance or seeming lack of change. This may be due to a true stop in action or to continuing actions which neutralize each other, resulting in no net change.

Equilibrium Shift: A change in the relative concentrations of reacting substances such that a different reaction or reaction rate is caused. For example, a change in the relative concentrations of sodium and calcium ions will dictate both the exchange rate and the selection of which ions will be adsorbed to and released from the ion exchange resin beads.

Equivalent Per Million: A unit of concentration used in chemical calculations and calculated by dividing the concentration in ppm (or mg/L) by the equivalent weight.

Equivalent Weight: The weight of a material (an element, compound, or ion) that yields (or per) one ionic valence charge. Equivalent weight is computed by dividing the atomic or molecular weight by the valence or number of reactive protons of the substance.
For an element, the equivalent weight is the atomic weight divided by the valence or number of reactive protons. For example, calcium (Ca) has an atomic weight of 40 and has two reactive protons (valence +2), so its equivalent weight is 40/2 = 20. For a compound, the equivalent weight is the molecular weight divided by the number of reactive protons (or positive valence in the compound). For example, sodium chloride (NaCl) has a molecular weight of 58.5 and one reactive proton (positive valence +1), so the equivalent weight is 58.5/1 = 58.5. Calcium carbonate (CaCO₃) has a molecular weight of 100 and two reactive protons (positive valence of +2 in the Ca²⁺ ion), so the equivalent weight is 100/2 = 50.
Equivalent weight is also called combining weight. Elements, compounds, and ions entering into combinations always do so in quantities proportional to their equivalent weights.

Erosion: The process in which a material is worn away by a stream of liquid (water) or air, often due to the presence of abrasive particles in the stream. Erosion is a physical or mechanical wearing away process rather than a chemical or electrochemical wearing away process (corrosion).

Ester: A compound formed by the reaction between an acid and an alcohol with the elimination of a molecule of water.

Etching: The deterioration by chemical change on the surface of glassware caused by the action of high temperatures and detergents, and that is more prevalent or intensified in soft or softened water supplies. Very high water temperatures in automatic dishwashers can cause detergent phosphate compounds to change into even more aggressive forms. If enough dish soil or water hardness is available, it will react with the most aggressive of these sequestering phosphates. Otherwise, however, the excessive detergent agents can actually extract elements directly from the glassware composition. In early stages, incipient etching appears as a rainbow-colored film similar to an oil-on-water film. As etching progresses, this changes to opaqueness, which appears similar to filming except that it cannot be removed or repaired since etching is an actual eating away of the glass. It is sometimes called “soft water filming.” The solution to chemical etching is to use less detergent, water temperatures below 140 degrees F, and sufficient amounts of water during the rinse cycle. (Poor rinsing can also be caused by overloading the dishwasher.) Mechanical etching can occur when two glasses rub against each other in the dishwasher.

Ethanol: See Ethyl Alcohol

Ethyl Alcohol: The most common variety of alcohol; also called grain alcohol and ethanol. Ethyl alcohol has good solvent and antifreeze properties and is soluble at all concentrations in water.

Etiology: The cause of a disease.

Eutrophic: Reservoirs and lakes which are rich in nutrients and very productive in terms of aquatic animal and plant life.

Eutrophication: The increase in the nutrient levels of a lake or other body of water; this usually causes an increase in the growth of aquatic animal and plant life.

Evaporation Chamber: That part of a distillation system in which water is changed into vapor.

Evaporite: A mineral precipitated as a result of evaporation, such as the solids left behind in the distillation process.

Evapotranspiration: The combined processes of evaporation and transpiration. It can be defined as the sum of water used by vegetation and water lost by evaporation.

Exchange Capacity: See Rated Capacity

Exchange Sites: Locations on each bead of ion exchange resin which hold mobile ions that are available for exchange with other ions in the solution that passes through the resin bed. In cation water softening, for example, mobile sodium ions located at the various exchange sites are exchanged for calcium, magnesium, iron, or other polyvalvent cations in the water being softened. Exchange sites are also called functional groups.

Exchange Tanks: See Portable Exchange Tanks

Exchange Velocity: The rate at which one ion is displaced in favor of another in an ion exchanger.

Exchanger: See Ion Exchanger

Exclusion Chromatography: See High Performance Liquid Chromatography

Exemption: A state with primary enforcement responsibility under the U.S. Safe Drinking Water Act may relieve a public water system from a requirement respecting an MCL, treatment technique, or both, by granting an exemption if certain conditions exist. These are:
1. The system cannot comply with an MCL or treatment technique due to compelling factors which may include economic factors;
2. The system was in operation on the effective date of the MCL or treatment technique requirement;
3. The exemption will not result in an unreasonable public health risk.

Exhaustion: The state of an ion exchanger or other adsorbent that is no longer capable of useful ion exchange due to the depletion of the initial supply of available exchangeable ions. A unit that is “exhausted” requires regeneration to restore its capacity to treat water.

Exhaustion Wave Front: The boundary between the absence and presence of a contaminant as it passes through a media bed.

Exothermic: A term used to describe a chemical process in which heat is released. For example, combustion is an exothermic process because heat is released.

Exposure: Contact with a chemical or physical agent.

Exposure Assessment: The determination or estimation (qualitative or quantitative) of the magnitude, frequency, duration, route, and extent (number of people) of exposure to a chemical.

Exposure Coefficient: Term which combines information on the frequency, mode, and magnitude of contact with contaminated medium to yield a quantitative value of the amount of contaminated medium contacted per day.

Exposure Level: The amount (concentration) of a chemical at the absorptive surfaces of an organism.

Exposure Scenario: A set of conditioners or assumptions about sources, exposure pathways, concentrations of toxic chemicals and populations (numbers, characteristics, and habits) which aid the investigator in evaluating and quantifying exposure in a given situation.

External Water Treatment: A term used in boiler water treatment referring to the “outside” (that is, not inside the boiler) preparation of the source water to be used for boiler feedwater or boiler makeup water. This preparation may include such steps as cation exchange softening, pH modification, or dealkalization.

Extrapolation: Estimation of unknown values by extending or projecting from known value.

FAC: Free Available (residual) Chlorine

FMA: Free mineral acidity

FPS: Feet (foot) per second

Fabric Softener: A laundry additive that gives fabrics a soft feel and smooth surface, reduces static electricity and wrinkling, and makes ironing easier. Most fabric softeners are designed for addition to the wash, rinse, or drying cycles. Wash- and rinse-added types are liquids; dryer-added fabric softeners come as sprays, impregnated tear-off sheets, and impregnated foam (porous) sheets, or as a slow-dispensing solid bar that attaches to the fin of a dryer. The softening agent most commonly used is a cationic quaternary ammonium compound. A fluorescent whitening agent or bluing is frequently included, as well as fragrance. Infrequently, antimicrobial ingredients are added. Fabric softening ingredients also are incorporated in some laundry detergent products.

Facultative Organisms: Facultative microbes can use either molecular (dissolved) oxygen or oxygen obtained from food material such as sulfate or nitrate ions. In other words, facultative organisms can live under aerobic or anaerobic conditions.

Fahrenheit: A temperature scale in which water freezes at 32 degrees and boils at 212 degrees at atmospheric pressure.

Fast Rinse: A rinse process in which the rinse water is applied to the softener bed at the end of brine regeneration at a faster rate of flow than that for which the brine was applied. Because of the greater density of the brine, it moves down through the bed in a piston-like fashion. If rinsing were to continue at this rate until the chlorides had dropped to the acceptable level at which the unit could be returned to service, the time required would be excessive. After the higher concentrations of brine have passed from the unit, little is gained by prolonging the rinse time. The rinse rate during the last few minutes is increased approximately fivefold to complete the rinse cycle. This fast rinse quickly removes the last traces of chlorides and significantly reduces the regeneration time.

Fatty Acids: The principal components in the molecular structure of natural fats, vegetable oils, fish oils, waxes, rosin, and essential oils, where they are bound chemically with glycerin; this combination is termed a glyceride.

Fatty Alcohol: Primary alcohols from C₆ to C₂₂, usually straight chain, which is the type used by the detergent industry.

Fecal Coliform Bacteria: Bacteria found in the intestinal tracts of mammals and, therefore in, fecal matter. Their presence in water or sludge is an indicator of pollution and possible contamination by pathogens.

Fecal Matter: Matter (feces) containing or derived from animal or human bodily wastes that are discharged through the anus.

Fecal Streptococcus: Streptococcus bacteria found in fecal matter

Feed Pressure: The pressure at which water is supplied to a water treatment device.

Feed Pressure: The pressure at which water is suppled to a water trestment device

Feed-and-Bleed: An ultrafiltration term borrowed from old-fashioned boiler operators. When applied to an ultrafilter design, it means multiple stages of ultrafilter units where the feedwater is controlled at a rate equal to the permeate plus concentrate flow rates and the reject water from the initial ultrafiltration stages is recirculated to subsequent stages.

Feedback: The circulating action between a sensor measuring a process variable and the controller which controls or adjusts the process variable.

Feedwater: The water to be treated that is fed into a given water treatment system.

Fermentation: The conversion/breakdown of organic matter by anaerobic bacteria into carbon dioxide, methane, and similar compounds of low-molecular weight.

Ferric Iron: Small solid iron particles containing trivalent iron, usually as gelatinous ferric hydroxide [Fe(OH)₃] or ferric oxide (Fe₂O₃), which are suspended in water and visible as “rusty water.” Ferric iron can normally be removed by filtration. Also called precipitated iron.

Ferrous Iron: A divalent iron ion, usually as ferrous bicarbonate [Fe(HCO₃)₂] which, when dissolved in water, produces a clear solution. It is usually removed by cation exchange water softening. Also called clear water iron.

Ficks Law of Diffusion: A law of chemistry and physics: the rate of diffusion of one substance in another is proportional to the negative gradient of the concentration of the first substance.

Filming: See Water Spotting

Filter: A device installed as part of the water system through which water flows for the purpose of removing turbidity, taste, color, iron, or odor. Filters can be loose media beds in tanks or cartridge-type devices (either packed-medium cartridges or membrane cartridges) and filter media may be used for mechanical, adsorptive, neutralizing, or catalyst/oxidation filtration processes.

Filter Aid: An agent (such as diatomite) that improves filtering effectiveness in some way, such as enhancing the retention of particles or increasing the permeability of the filter to water flow. A filter aid is either added to the suspensions to be filtered or placed on the filter as a layer through which the liquid must pass.

Filter Area: The effective area, expressed in square feet, through which water approaches the filter media. Also called surface area.

Filter Cake: 1. Solids deposited on top of a filter media bed, often by use of chemically feeding a coagulant or filter aid.
2. The dewatered residue from a filter, centrifuge, or other dewatering device.

Filter Media: The selected materials in a filter that form the barrier to the passage of filterable suspended solids or dissolved molecules. Filter media are used to remove undesirable materials, tastes, and odors from a water supply and to adjust the pH in a water supply. Filter designs include:
1)loose media filters with grains, resin, or other particles lying in beds or loosely packed in column-form in tank-type filters; or
2)cartridge-type filters which may contain membranes, fabric, fiber, bonded-ceramic, precoat, or cast solid-block filter media. The media used in some filters are chemically inert, such as sand, which performs only a mechanical filtration. Other filter media are multifunctional, chemically-reactive media such as calcite, activated carbon, magnesia, manganese dioxide, and manganese greensand.

Filter Rating: See Micron Rating

Filter-Ag: The trade name for an aluminum silicate (pumicite) granular product used as a general purpose filter medium.

Filtrate: 1. The effluent liquid from a filter system; that part of the feed stream which has passed through the filter.
2. The liquid remaining after removal of solids, as the liquid extracted in the formation of a filter cake.

Filtration: The process of separating solids from a liquid by means of a porous substance such as a permeable fabric or membrane or layers of inert media.

Fines: Extremely small particles which are smaller than the specified size (in millimeters) for the medium. Fines may be formed in the manufacturing process, may result from breakdown of medium particles (ion exchange resins or activated carbon) during service, or may result from the dissolving of a medium such as calcite. An excess of fines in a filter, softener, or deionizer can create undesirable pressure drop in the system, cause sloughing of particles, or create undesirable qualities in the filter effluent.

Finished Water: Product water as it leaves the municipal treatment plant for delivery to consumers. When it arrives at the point-of-use, it has become delivered water. Also called product water.

First Draw: The water that immediately comes out when a tap is first opened. This water is likely to have the highest level of lead contamination from plumbing materials.

First Draw Sample: A one-liter sample of tap water, collected in accordance with CFR Section 141.86(b)(2), that has been standing in plumbing pipes at least six hours and is collected without flushing the tap.

Fission: As relates to biology, reproduction by cell division.

Fix, Sample: A sample is fixed in the field by adding chemicals that prevent the water quality indicators of interest in the sample from changing before final measurements are performed later in the lab.

Fixed Bed: 1. The filter or ion exchange medium retained in a vessel.
2. Also refers to media beds which are “contained”. That is, filled to the top or to the restraining barrier with filter media and not capable of being expanded during backwashing.

Fixed Matter: The residue (particulate and/or dissolved material) that remains behind (immovable or fixed) despite action to expel it, such as the residue remaining after heating or burning a substance to drive off the volatile solids.

Fixed Solids: The term used in the laboratory analysis of the solid’s content of water to define the residue of total suspended and/or dissolved solids after ignition (burning) or heating for a specified time at a specified temperature.

Fixture: As relates to plumbing, any permanently-installed receptacle that will hold water, such as a sink, lavatory, or water closet (toilet).

Fixture Count: A count of the total number of plumbing fixtures (or water outlets) in a building. A fixture count is determined for the purpose of estimated peak flow rates and sizing equipment, especially for commercial or institutional buildings.

Flagellates: Microorganisms that move by the action of tail-like projections.

Flame Polished: Melted by a flame to smooth out irregularities. Sharp or broken edges of glass (such as the end of a glass tube) are rotated in a flame until the edge melts slightly and becomes smooth.

Flash: The portion of a superheated fluid that is converted to vapor when its pressure is reduced as in flash distillation.

Flash Distillation: A distillation process in which hot incoming water flows into a chamber in which pressure is low, causing some of the water to flash (turn quickly into steam.)

Floc: As relates to water treatment, avery fine, fluffy-type mass formed by the coming together of a number of fine suspended particles. A floc can occur naturally, but most frequently it is induced by the addition of a coagulant/flocculent to raw water which contains undesirable turbidity or color. In wastewater treatment, a clump of solids formed in sewage by biological or chemical action.

Floc: A very fine, fluffy-type mass formed by the coming together of a number of fine suspended particles. A floc can occur naturally, but most frequesntly it is induced by the addition of a coagulant/flocculent to raw water which contains undesirable turbidity of color.

Floc (Water Treatment): A very fine, fluffy-type mass formed by the coming together of a number of fine suspended particles. A floc can occur naturally, but most frequesntly it is induced by the addition of a coagulant/flocculent to raw water which contains undesirable turbidity of color.

Floc (waste water treatment): A clump of solids formed in sewage by biological or chemical action.

Flocculation: The process of bringing together destabilized or coagulated particles to form larger masses or flocs (usually gelatinous in nature) which can be settled and/or filtered out of the water being treated.

Flocculents: Materials which when added to water cause suspended particles to coagulate into larger groupings and form gelatinous clouds of precipitate which enclose additional fine particles of suspended dirt. The precipitate and the dirt can then be settled or filtered out of the water being treated.

Flood Plain: The flat or nearly flat land on the floor of a stream valley or tidal area that is covered by water during floods.

Flood Rim: The edge of a receptacle (such as a plumbing fixture) from which water will overflow.

Flow Control Valve: A cylindrical pressure-compensating valve installed to regulate the flow of water. Rated in gpm or gpd.

Flow Controller: An in-line device or orifice fitting which will regulate and control flow of water or regenerant over a broad range of inlet water pressures. Some types are manually adjustable.

Flow Meter: An instrument, mechanical or electronic, used for recording (in gallons, cubic feet, or cubic meters) the quantity of water passing through a particular pipe line or outlet. In water processing systems, meters may initiate certain functions such as automatically starting the regeneration cycle in an ion exchange system.

Flow Rate: The quantity of water or regenerant which passes a given point in a specified unit of time, often expressed in U.S. gpm (or L/min). In filters, flow rate is usually measured in gpm/sq.ft. of bed area. In ion exchangers, it is expressed in gpm/cu.ft. of resin. Flow rate is a critical design parameter by which the effectiveness of the water treatment unit is measured.

Flow Sensor: A device that measures flow rate and can control or measure an action (such as chemical feed) in proportion to the flow rate of the fluid.

Flow Switch: A device which, according to a preset flow rate condition, causes an action when the actual flow rate falls outside the preset limit(s).

Fluidized: A mass of solid particles that is made to flow like a liquid by injection of water or gas is said to have been fluidized. In water treatment, a bed of filter media is fluidized by backwashing water through the filter.

Fluidized Bed: A medium bed which has become expanded during the backwash step or during “upflow” regeneration of an ion exchanger.

Flume: A raceway or channel constructed to carry water or to permit the measuring of its flow.

Fluorescein: An orange-red compound that exhibits intense fluorescence in alkaline solutions and is used to dye water in order to trace its course and movement.

Fluoridation: The addition of a chemical to increase the concentration of fluoride ions in drinking water to a predetermined optimum limit to reduce the incidence (number) of dental caries (tooth decay) in children. Defluoridation is the removal of excess fluoride in drinking water to prevent the mottling (brown stains) of teeth.

Fluoride: A naturally-occurring constituent of some water supplies, an excess of which (over 2.0 ppm) can cause discolored teeth (mottling). Skeletal fluorosis, a serious crippling bone disorder resembling osteoporosis, can develop from many years of exposure to drinking water with more than 4.0 ppm of fluoride.

Fluorosis: An abnormal condition caused by excessive intake of fluorine, characterized chiefly by mottling of the teeth.

Flush: 1. To open a cold-water tap to clear out all the water which may have been sitting for a long time in the pipes. In new homes, to flush a system means to send large volumes of water gushing through the unused pipes to remove loose particles of solder and flux.
2. To force a cleansing liquid rapidly through piping, tubing, storage vessels, process tanks, or other plumbing items to clean them out.

Flush Tank: The chamber of the toilet in which the water is stored for rapid release to flush the toilet. The size of the flush tank is to be accounted for in proper sizing of any plumbing system or water treatment system.

Flush Valve (Flushometer): A self-closing valve used for flushing urinals and toilets in public buildings. This type of valve allows very high flow rates (15-20 gpm) for a few seconds.

Flushing: In municipal water systems, a method used to clean water distribution lines. Hydrants are opened and water with a high velocity flows through the pipes, removes deposits from pipes, and flows out the hydrants.

Flux: In cross flow filtration, the flow rate of product water through a reverse osmosis, electrodialysis, or ultrafiltration membrane. The flow rate is usually given in terms of volume unit per time per membrane area, such as gallons per day per square foot or liters per hour per square meter.

Fluxing Lime: See Lime (CaO)

Fluxion: The trade name for a patented medium composed of high purity copper and zinc granules. KDF is capable of removing chlorine, soluble heavy metals, and other inorganic contaminants from water through the chemical reduction/oxidation (redox) process.

Foam: A mass of bubbles formed on liquids by agitation.

Foot Valve: A water softener valve, controlled by a float, which controls the amount of water entering or brine solution leaving the brine tank. A special type of check valve located at the bottom end of the suction pipe on a pump. This valve opens when the pump operates to allow water to enter the suction pipe but closes when the pump shuts off to prevent water from flowing out of the suction pipe.

Forced-Draft Degasifier: A tall column wherein water is sprayed downward through an upward flow of air for the purpose of removing gases such as carbon dioxide after the decationization unit in a deionization plant.

Formaldehyde: Formic aldehyde methanol, HCHO₃, made by oxidation of synthetic methanol or low-boiling petroleum gases such as propane or butane. Available commercially as a 37-50 percent aqueous solution which may contain up to 15 percent methanol to inhibit polymerization. Commercial grades are called formalin. An effective preservative, disinfectant, and sanitizing agent, although it is not a sterilizer, because formaldehyde does not kill completely all microorganisms. Is not typically used to sanitize drinking water treatment equipment because of personal hazards associated with it i.e., toxic by inhalation, strong irritant, and a carcinogen.

Formalin: Commercial grades of formaldehyde.

Formation: A group of similar consolidation (that is, relatively solid) rocks of unconsolidated (that is, relatively loose) minerals.

Fouling: In electrodialysis applications, the deposit of organic or other materials on the surface of the electrodialysis membrane surface, causing membrane inefficiencies. As relates to filtration or ion exchange, the accumulation of undesirable foreign matter in a filter or ion exchange media bed causing clogging of pores or coating of surfaces and inhibiting or limiting the proper operation of the bed and the treatment system. In reverse osmosis or ultrafiltration applications. a phenomenon in which a reverse osmosis or ultrafiltration membrane adsorbs, interacts with, or becomes coated by solutes and/or precipitates in the feed stream resulting in a decrease in membrane performance by lowering the flux and/or affecting the rejection of solutes.

Fouling (electrodialysis): The deposit of organic or other materials on the surface of the electrodialysis membrane, causing membrane inefficiencies.

Fouling (filtration/ion exchange): The accumulation of undesirable foreign matter in a filter or ion exchange media bed causing clogging of pores or coating of surfaces and inhibiting or limiting the proper operation of the bed and the treatment system.

Fouling (reverse osmosis/ultrafiltration): A phenomenon in which a reverse osmosis or ultrafiltration membrane absorbs, interacts with, or becomes coated by solutes and/or precipitates in the feed stream resulting in a decrease in membrane performance by lowering the flux and/or affecting the rejection of solutes.

Fractionate: To separate into fractions or parts.

Free Acid Form: The regenerated form of a weak acid cation exchanger.

Free Available (Residual) Chlorine (FAC): That portion of the total available residual chlorine composed of dissolved chlorine gas (Cl₂), hypochlorous acid (HOCl), and/or hypochlorite ion (OCl^–) remaining in water after chlorination. This does not include chlorine that has combined with ammonia, nitrogen, or other compounds.

Free Base Form: The regenerated form of a weak basic anion exchanger.

Free Carbon Dioxide: Carbon dioxide present in water as gas or as carbonic acid but not including that carbon dioxide in combination as in carbonates or bicarbonates.

Free Mineral Acidity: Acidity in water due to the presence of strong inorganic acids like hydrochloric, nitric, and sulfuric acids, as opposed to weak acidity due to such acids as carbonic or acetic. Mineral acidity is usually expressed in water analysis as FMA.

Free Residual Chlorination: The application of chlorine to water to produce a free available chlorine residual equal to at least 80 percent of the total residual chlorine (sum of free and combined available chlorine residual).

Freeboard: The vertical distance between the top of a filter media bed (or ion exchange resin bed) and the overflow or collector. This space allows for bed expansion during backwashing. The distance may be expressed in linear measurement or as a percent of the bed depth.

Fresh Water: Water having less than approximately 1,000 mg/L (ppm) of total dissolved solids (TDS).

Friability: An expression of the ability of ion exchange beads to resist cracking under hydrostatic operation.

Friction Losses: The head, pressure, or energy (they are the same) lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water and the roughness of the pipe, channel walls, and restrictions caused by fittings. Water flowing in a pipe loses pressure or energy as a result of friction losses.

Fullers Earth: A clayish substance of hydrous aluminum silicate used as a filter aid in coagulation.

Fulvic Acid: A water-soluble, natural organic substance of low molecular weight which is derived from humus often found in surface water. Fulvic acid contributes to the formation of trihalomethanes in chlorinated water supplies and can contribute to organic fouling of ion exchange resin beds. Fulvic acids are chelating agents that can bind and hold metal ions in solution, and are particularily involved in the solubilization and transport of iron in water. Fulvic acid compounds are associated with color in water. These yellow-brown materials frequently are encountered along with soluble iron.

Functional Groups: See Exchange Sites

Fungi: (singular = fungus) Mushrooms, molds, mildews, rusts, and smuts that are small nonchlorophyll-bearing plantlike organisms lacking roots, stems, and leaves. They have distinct nuclei surrounded by nuclear membranes as well as other specialized functional cell parts but cannot carry on photosynthesis. They occur in natural waters and grow best in the absence of light. Their decomposition may cause objectionable tastes and odors in water.

GA Salt: A very coarse grainy salt of “Ground Alum” size, which was formerly used for regenerating zeolite water softeners, sometimes used coincidentally with alum as a coagulant.

GRAS: Designation for materials listed by the U.S. Food and Drug Administration (FDA) as “generally regarded as safe.”

Gallionella Ferruginea: One of several types of bacteria that use iron in their metabolism and are capable of depositing gelatinous ferric hydroxide.

Gallon: The common U.S. unit of measurement of liquid volume. (The international unit of volume measurement is the liter.) One U.S. gallon has a volume of 231 cubic inches or 3.785 liters. The Imperial (British) gallon equals 277.418 cubic inches or 4.546 liters.

Galvanic Cell: A cell, consisting of dissimilar metals in contact with each other and with an electrolyte, which generates an electrical current.

Galvanic Corrosion: A form of corrosion which occurs in a galvanic cell in which one of the metals dissolves and goes into solution. This form of corrosion is accelerated by high concentrations of dissolved minerals in water that increase electrical conductivity. Galvanic corrosion may occur if two pipes of dissimilar metals are joined directly–without the use of a pipe fitting designed to insulate different metals from one another and prevent such corrosion of the pipes.

Galvanic Series: A list of metals and alloys presented in the order of their tendency to corrode (or go into solution). Also called the electromotive series. This is a practical application of the theoretical electrochemical series.

Galvanize: To coat a metal (especially iron or steel) with zinc. Galvanization is the process of coating a metal with zinc.

Gamma decay: A type of radiation, gamma radiation, where gamma rays are emitted and that usually accompanies alpha or beta decay. Gamma rays are photons, and are without rest mass or charge. Alpha or beta decay may simply proceed directly to the ground (lowest energy) state of the daughter nucleus without gamma emission, but the decay may also proceed wholly or partly to higher energy states (excited states) of the daughter. In the latter case, gamma emission may occur as the excited states transform to lower energy states of the same nucleus may transform to a lower energy state by ejecting an electron from the cloud surrounding the nucleus. This orbital electron ejection is known as internal conversion and gives rise to an energetic electron and often an x-ray as the atomic cloud fills in the empty orbital of the ejected electron. SEE ALSO alpha decay; beta-minus decay; beta-plus decay; photon; radioactivity.

Garnet: A group of hard, reddish, glassy, mineral sands made up of silicates of base metals (calcium, magnesium, iron, and manganese). Garnet has a higher density than sand.

Gas Chromatograph (GC): A chemical analytical instrument used to separate a sample into components during gas chromatography.

Gas Chromatography (GC): Chromatography in which the sample mixture is vaporized and injected into a stream of carrier gas such as helium or nitrogen (mobile phase) which is moving through a column containing solid medium or medium coated with a relatively nonvolatile liquid (stationary phase). The mobile phase sample is, thereby, separated into its component compounds according to the unique affinity of each compound for the stationary phase. The components appear separately at the effluent end of the column where they can be detected and measured by density differences, thermal conductivity changes, or ionization detectors. The detector gives a signal (in peak form) for each separated component compound; the intensity of the signal is proportional to the quantity of the compound injected, making it possible to provide a quantitative analysis by calibration.

Gastroenteritis: An inflammation of the stomach and intestine resulting in diarrhea, with vomiting and cramps when irritation is excessive. When caused by an infectious agent, it is often associated with fever.

Gate Valve: A type of valve in which the closing element (the gate) is a disc that moves across the stream in a groove or slot for support against pressure. A gate valve has relatively large full ports and a straight line flow pattern. A gate valve creates very little pressure drop; this valve is, however, subject to leakage if the sealing surfaces are scored or marred or if debris becomes lodged in the groove.

Gauge Pipe: A number that defines the thickness of the sheet used to make steel pipe. The larger the number, the thinner the pipe wall.

Gauge Pressure: The pressure within a closed container or pipe as measured with a gauge. In contrast, absolute pressure is the sum of atmospheric pressure (14.7 lbs/sq in) PLUS pressure within a vessel (as measured by a gauge). Most pressure gauges read in gauge pressure or psig (pounds per square inch gauge pressure).

Gavage: Type of exposure in which a substance is administered to an animal through a stomach tube.

Gel Resin: A “gellular resin” form of ion exchanger as opposed to macroporous exchangers. Gel resin is typically cross-linked with eight percent divinylbenzene.

Gel Zeolite: A synthetic sodium alumina silicate cation exchange product that was very widely used in residential water softeners prior to the development of DVB/styrene cation resin. Also called siliceous gel zeolite.

Geological Log: A detailed description of all underground features discovered during the drilling of a well (depth, thickness, and type of formations).

Geophysical Log: A record of the structure and composition of the earth encountered when drilling a well or similar type of test hole or boring.

Germicidal Ultraviolet: An ultraviolet light that peaks at a 2,537-angstrom wavelength and is in a wavelength that lies between 200 and 300 nanometers. This is known as the germicidal or short-wave ultraviolet band.

Giardia: A common waterborne protozoan that forms cysts and is resistant to disinfectants such as chlorine and ultraviolet light. Giardia can be removed by filters that capture all particles of four microns and greater in size.

Giardia Lamblia: Flagellate protozoan which is shed during its cyst stage into the feces of man and animals. When water containing these cysts is ingested, the protozoan causes a severe gastrointestinal disease called giardiasis.

Giardiasis: Intestinal disease caused by an infestation of Giardia flagellates.

Glaubers Salt: An anhydrous sodium sulfate (Na2SO4 10H2O) salt compound.

Glauconite: A natural dull-green iron potassium silicate mineral occurring abundantly in greensand. The approximate formula for glauconite is K15(Fe, Mg, Al)4-6(Si,Al)3O20(OH)4.

Globe Valve: A type of valve in which the closing element is a segment of a sphere or a flat or rounded gasket which is moved into or onto a round port. The globe valve usually has small ports, an “S” flow pattern and relatively high pressure drop. Globe valves provide tight dependable seals with minimum maintenance.

Glutaraldehyde: [OCH(CH₂)₃CHO] A general disinfectant for drinking water treatment equipment, including reverse osmosis membranes. Available as sporicidin and cidex, for example; requires full strength use for disinfection. A general disinfectant for drinking water treatment equipment, including reverse osmosis membranes. Available as sporicidin and cidex, for example; requires full strength use for disinfection.

Glycerin: A trihydroxy alcohol with sweet tast and syrup-like consistency; the “gylcerine” spelling has come into general use, but it is chemically incorrect.

Gooseneck: A portion of a service connection between the distribution system water main and a meter. Sometimes called a pigtail.

Grab Sample: A single sample collected at a particular time and place which represents the composition of the water only at that time and place.

Grade: The elevation of the invert of the bottom of a pipeline, canal, culvert, or similar conduit. The inclination or slope of a pipeline, conduit, stream channel, or natural ground surface usually expressed in terms of the ratio or percentage of number of units of vertical rise or fall per unit of horizontal distance. A 0.5 percent grade would be a drop of one-half foot per hundred feet of pipe.

Grain: A unit of weight equal to 0.0648 grams or 0.000143 pounds or 1/7000th of a pound.

Grains Per Gallon (gpg): A common method of reporting water analysis results in the United States and Canada. One grain per gallon equals 17.1 parts per million (ppm) or 17.1 milligrams per liter. Grains per Imperial gallon equals 14.3 mg/L (or ppm).

Gram: The basic unit of weight measurement in the metric system. One gram equals 0.0022 pounds or 15.432 grains. The gram was originally devised as the weight of one cubic centimeter or one milliliter of water at 4 degrees Centigrade.

Gram-milliequivalent: The equivalent weight (in grams) divided by 1,000.

Gravel Support Bed: Various layers of different sized gravel and coarse sand placed above the underdrain network to support filter or ion exchange media beds. The gravel support bed contributes greatly to the distribution and collection of product water and the even dispersal of the backwash water flow.

Gravimetric: A means of measuring unknown concentrations of water quality indicators in a sample by weighing a precipitate or residue of the sample.

Gravimetric Measurement: Measurement on the basis of weight.

Gray (Gy): The SI unit of absorbed dose of ionizing radiation. One gray (Gy) equals 100 rads.

Greensand: A naturally-occurring mineral that consists largely of dark greenish grains of glauconite and which possesses ion exchange properties. Greensand was the original product used in commercial and home cation exchange water softening units and was the base product for manufacturing manganese greensand zeolite products.

Grey Water: Waste water other than sewage, such as sink drainage or washing machine discharge.

Gross Alpha Particle Activity: The total radioactivity due to beta particle emission as inferred from measurements on a dry sample.

Gross Beta Particle Activity: The total radioactivity due to beta particle emission as inferred from measurements on a dry sample.

Groundwater: Water found beneath the surface of the ground. Groundwater is primarily water which has seeped down from the surface by migrating through the interstitial spaces in soils and geologic formations.

Grouting: Cement-like fluid which is poured or injected into the bore hole during well drilling to seal crevices and to prevent contamination or loss of drilling mud. Grouting provides protection around the metal well casing and helps prevent corrosion and infiltration into the well bore hole from surface water and shallow groundwater. Grouting can sometimes improve the strength and elasticity of the rock formation itself.

Gulmite Screw: The screw which holds the swivel part of a yoke connector for a portable exchange tank in place.

Gypsum: (CaSO₄ 2H₂O) A moderately insoluable calcium sulfate, containing 20.9 percent water, which is often used as a soil amendment to aid in building soil structure and permeability. A moderately insoluble calcium sulfate, containing 20.9 percent water, which is often used as a soil amendment to aid in building soil structure and permeability.

H2O: The chemical formula for water (dihydrogen oxide).

HPC: Heterotrophic Plate Count

HPLC: High Performance Liquid Chromatography (same as high pressure liquid chromatography)

HTH: (pronounce as separate letters): High Test Hypochlorite. Calcium hypochlorite or Ca(OCl)₂. “HTH” is a trademark (Olin) for a high-test calcium hypochlorite product containing 70 percent available chlorine that is commercially available in both water-soluble granular and tablet form.

Half-life: The time required for half of the substance present at the beginning to dissipate or disintegrate.

Halite: A geological term for rock salt, a mineral which is more than 95 percent sodium chloride (NaCl). Also called native salt or fossil salt.

Halogens: A family group of elements, including bromine, chlorine, fluorine, astatine, and iodine, which are extremely active chemically. These elements exist in the free state normally as diatomic molecules, but more commonly are found as the ionic component in compounds with various other elements.

Halophilic: Thriving in a salt environment.

Halophilic Bacteria: Salt-tolerant bacteria often found in solar salt which has not been fully kiln dried or in salt which may have been exposed to unsanitary conditions over a long period of time.

Hard Water: Water containing a total mineral hardness (typically from calcium and magnesium ions) of one grain per U.S. gallon (1gpg = 17.1 ppm) or more measured as calcium carbonate equivalent. SEE ALSO hardness.

Hardness: Hardness is a measurable property of water brought about by the presence of calcium and magnesium ions (and other multivalent metallic ions) that can cause scale formation, soap curd, water spotting, and harshness in fabrics laundered in such water. The term was colloquially used to describe certain waters that caused difficulty in using soap; i.e. “this water makes soap hard to lather”.

Hardness is expressed in grains per US gallon (gpg) where 1 grain equals 17.1 ppm as calcium carbonate equivalent. The degree of hardness expressed in gpg that is generally accepted:

Less than 1 gpg is termed as soft water
1.0 to 3.5 gpg is slightly hard
3.5 to 7.0 gpg is moderately hard
7.0 to 10.5 gpg is termed as hard
Above 10.5 gpg is very hard.

While many divalent and trivalent metallic cations can potentially contribute to “hard water” symptoms, the most commonly referenced “hardness” contaminants are calcium and magnesium ions in water, expressed as calcium carbonate (CaCO₃).

In practice, when sizing a water conditioner for the removal of hardness in residential applications, it is common to count only the calcium and magnesium content in calculating the hardness load. “Total” hardness would include iron, manganese, strontium, barium and radium plus the common hardness. In certain applications requiring very low hardness residuals, if the total hardness exceeds the common hardness by more than 1 percent, specific design treatment or pretreatment and/or regeneration schemes are employed to prevent fouling of the system as a result of the marginal solubility of the heavier elements.

SEE ALSO carbonate hardness; noncarbonate hardness; total hardness.

Hardness as Calcium Carbonate: The value obtained when the hardness-forming salts are calculated in terms of equivalent quantities of calcium carbonate. This method of water analysis provides a common basis for comparison of different salts and compounds.

Hazard Evaluation: A component of risk assessment that involves gathering and evaluating data on the types of health injury or disease (e.g., cancer) that may be produced by a chemical and on the conditions of exposure under which injury or disease is produced.

Head: The pressure at any given point in a water system, generally expressed in pounds per square inch (psi). May also be called pressure head or velocity head. Head is calculated as the pressure exerted by a hypothetical column of water standing at the height to which the free surface of water would rise above any point in a hydraulic system. For this reason, head is sometimes expressed as the height of a column of water which would produce a given pressure; this measurement may be called hydrostatic head. The pressure head in feet of water is equal to the pressure in psi times 2.31 ft/psi.

Head Loss: The reduction of water pressure (head), measured in psi, in a hydraulic or plumbing system. Head loss is a measure of the resistance of the medium bed (or other water treatment system) and/or plumbing system to the flow of the water through it. In water treatment technology, head loss is basically the same as pressure drop.

Header: A large central pipe with two or more side outlets which is located at the bottom of a vessel containing water that has passed through a filter bed or ion exchange media bed. One purpose of the header is to collect the processed product water, but the header may also be used to distribute backwash water and regenerants across the bottom of the bed area.

Health Contaminant: Any substance or condition that may have any adverse effect on human health. Health contaminants in water are regulated as part of the National Primary Drinking Water Regulations enforced by the U.S. Environmental Protection Agency and most states.

Health Effects Concern: Exposure to contaminant at a toxicologically significant level as defined by the maximum contaminant levels (MCLs) for regulated contaminants or action for nonregulated contaminants.

Heat Exchanger: An apparatus used to transfer heat from one medium to another or used to remove heat from or add heat to a fluid.

Heat Sensor: A device that opens and closes a switch in response to changes in the temperature. This device might be a metal contact, or a thermocouple which generates a minute electrical current proportional to the difference in heat, or a variable resistor whose value changes in response to changes in temperature. Also called a temperature sensor.

Heat of Vaporization: The amount of additional (latent) heat needed to change a given amount of liquid existing at its boiling point temperature into a vapor.

Heavy Metals: Metallic elements with high atomic weights, e.g., mercury, chromium, cadmium, arsenic, and lead. They can damage living things at low concentrations and tend to accumulate in the food chain.

Hectare: A measure of area in the metric system similar to an acre. One hectare is equal to 10,000 square meters and 2.4711 acres.

Heel: In ion exchange applications, the lower zone of the ion exchange bed that is “passed by” in either the softening, deionization, or dealkalization mode or during the application of regenerants. This condition is usually due to the configuration of the vessel or the lack of a good underdrain distribution system.

Hematopoeisis: The production of blood and blood cells: hemopoiesis.

Heme: A deep red pigment (C₃₄H₃₂N₄O₄Fe) which contains reduced (ferrous) iron. Heme is found in red blood cells (hemoglobin). It is also found outside the body in the nonprotein portions of some organic molecules called hemoproteins. In water quality treatment, it may be referred to as heme iron, which is organically-bound iron that can cause water to have a pinkish cast to it.

Hemodialysis: The process of purifying a kidney patient’s blood by means of a dialysis membrane.

Hemodialysis Grade Water: Water which meets the requirements set forth by the American National Standards for Hemodialysis Systems and covered in the Association for the Advancement of Medical Instrumentation (AAMI) standards.

Hemolysis: The rupturing of red blood cells which sometimes occurs during hemodialysis. Hemolysis may be caused by the presence of chloramines in dialysis water.

Henrys Law: A law of chemistry that states that the weight of a gas dissolved (at a given temperature) in a liquid is proportional to the pressure of the gas above the liquid.

Hepatic: Pertaining to the liver.

Hepatitis: Hepatitis is an inflammation of the liver usually caused by an acute viral infection. Yellow jaundice is one symptom of hepatitis.

Hepatoma: A malignant tumor occurring in the liver.

Herbicide: A compound, usually a man-made organic chemical, used to kill or control plant growth.

Hertz (Hz): The number of complete electromagnetic cycles or waves in one second of an electrical or electronic circuit. Also called the frequency of the current. Abbreviated Hz.

Heterocyclic: A type of organic compound in which the characteristic chemical groups are linked in a closed ring structure and in which one or more atoms in the ring is an element other than carbon, e.g., silica, sulfur, nitrogen, etc.

Heterotrophic: heteros, other + trophe, nourishment. Obtaining food or nourishment from other organisms. Heterotrophic organisms or heterotrophs are consumers such as man or decomposers such as bacteria that obtain their nourishment and energy from the organic molecules manufactured by the autotrophic organisms (the producers). All animals, for example, are consumers and heterotrophs that depend on complex organic molecules produced by autotrophs for their food and energy.

Heterotrophic Microorganisms: Bacteria and other microorganisms that use organic matter synthesized by other organisms for energy and growth.

Heterotrophic Plate Count (HPC): A procedure for estimating the total number of live nonphotosynthetic bacteria in water. Colony-forming units (CFU) are counted after spreading an aliquot portion of a sample over a membrane or pour plate and incubating in an amiable growth medium (agar) and at an amiable temperature. (These generally are not considered to be disease-causing bacteria.)

Hexametaphosphate: A chemical that is used as a sequestering agent. Normally, a metal (M) hexametaphosphate would have the chemical formula (MPO₃)₆, in which the cyclic metal metaphosphate is based on rings of alternating phosphorus and oxygen atoms. The so-called sodium hexametaphosphate, however, is probably a polymer with the formula (NaPO₃)_n, in which n is between 10 and 20. Hexametaphosphate is added to water to increase the solubility of certain ions and to deter precipitation of certain chemicals.

High Frequency Ozonation: Operation of an ozone generator at frequencies equal to or greater than 1,000 cycles per second or 1,000 hertz.

High Line Jumpers: Pipes or hoses connected to fire hydrants and laid on top of the ground to provide emergency water service for an isolated portion of a municipal distribution system.

High Performance Liquid Chromatography (HPLC): A general term applied to modern instrumental techniques adopted to greatly increase the scope and precision of the liquid chromatography analytical method. Among the varied HPLC techniques are: Reversed phase chromatography, which uses a polar liquid phase for elution of a column containing a nonpolar phase. This technique is used, for example, to analyze the polynuclear aromatic hydrocarbon category (pyrenes, naphthalenes, etc.) of synthetic organic compounds; Ion exchange chromatography, which makes it possible to separate large numbers of cations and anions; Exclusion chromatography, which separates, on a porous gel, compounds according to their size and makes it possible to determine their apparent molecular weights and to separate fractions of different molecular weights for further analyses.

High Salting: The use of 15 pounds or more of salt (NaCl or KCl) to regenerate each cubic foot of cation resin. High salting is generally recommended for high total hardness water and water containing high concentrations of dissolved heavy metals.

High Voltage Electrode: As relates to ozonation, the outlet post on the voltage transformer which produces more than 1,000 volts.

High-Frequency Ozonation: Operation of an ozone generator at frequencies equal to or greater than 1,000 cycles per second or 1,000 hertz.

High-to-Low Dose Extrapolation: The process of prediction of low exposure risks to rodents from the measured high exposure-high risk data.

Histology: The study of the structure of cells and tissues; usually involves microscopic examination of tissue slices.

Homogenous: Having the same composition throughout. Homogenized milk is homogeneous because the fat globules have been broken into smaller colloid-sized particles that remain distributed throughout the liquid milk. In nonhomogenized milk, the fat globules rise to the top of the container as cream.

Hose Bib: Faucet. A location in a water line where a hose is connected.

Hot Lime-Soda Softening: A method of partially softening water by adding lime and soda ash to chemically precipitate the calcium, magnesium, iron, and silica at a water temperature of about 212 degrees Fahrenheit. This process also drives off carbon dioxide.

Hot Process Softening: A term used to encompass several softening/clarifying processes using lime, lime and soda ash, or lime and cation softening to treat water which is at or near the boiling point. Hot process softening can remove carbon dioxide, silica, and precipitated magnesium and is used mainly for boiler feedwater preparation and sulfur mining.

Hot-Lime Softening: A partial softening method which requires adding a lime slurry to water which is at about 212 degrees Fahrenheit and then chemically precipitating and removing the calcium and magnesium hardness via sedimentation and filtering.

Human Equivalent Dose: A dose which, when administered to humans, produces an effect equal to that produced by a dose in animals.

Human Exposure Evaluation: A component of risk assessment that involves describing the nature and size of the population exposed to a substance and the magnitude and duration of their exposure. The evaluation could concern past exposures, current exposures, or anticipated exposures.

Human Health Risk: The likelihood (or probability) that a given exposure or series of exposures may have or will damage the health of individuals experiencing the exposures.

Humic Acid: Humic substances that are soluble in strong base solutions but insoluble in acidified (to pH < 2) water, and that affect water quality through exchange of species, such as cations or organic materials.

Humic Substances: The organic portion of soil that remains after prolonged microbial decomposition, and that is formed by the decay of leaves, wood, and other vegetable matter. Humic substances can impart a yellowish-brown to brownish-black color to water; detectable to 0.1 ppm in water. Humic substances are commonly classified on the basis of solubility. If a material containing humic substances or humus is extracted with a strong base and the resulting solution is then acidified, the products are a) a nonextractable plant residue called humin, b) a material called humic acid that precipitates from the acidified (pH < 2) solution, and c) an organic material called fulvic acid that remains dissolved in the acidified solution. The high molecular weight and polyelectrolytic humic substance macromolecules range from a molecular weight of a few hundred for fulvic acid to tens of thousands for the humic acid and humin fractions. Humic substances form suspected-carcinogenic trihalomethanes (THMs, such as chloroform, dibromochloromethane, bromodichloromethane, and bromoform) by reaction with chlorine. Humic substances are excellent chelating agents that bind with and hold metal ions in water, and they also effectively exchange cations with water.

Humidification: The process of increasing the water vapor or moisture content.

Humin: Humic substances that remain insoluble in both strong base solutions and in water. Humins can effectively exchange cations with water and may accumulate quantities of metals. Lignite coal, for example, is largely a humin and humic-acid material, which, through ion exchange, tends to remove some metal ions from water.

Hydrate: A substance formed by combining water with a compound.

Hydrated Lime: Ca(OH)₂ A strong alkali chemical, calcium hydroxide, obtained by treating (slaking) lime with water in a heat-producing reaction until the calcium oxide has been converted to calcium hydroxide. Hydrated lime is used in lime softening water treatment. Also called calcium hydrate; calcium hydroxide; caustic lime; slaked lime.

Hydration: The chemical combination of water into another substance.

Hydraulic: Referring to water or other fluids in motion.

Hydraulic Classification: The rearrangement, during backwashing, of ion exchange or other media particles according to size. As the result of classification, the smallest particles tend to rise to the top of the bed while the largest tend to sink to the bottom because of weight or surface area ratio.

Hydraulic Conductivity: The capacity of rock or soil formations to transmit water to a pumping well. Capacity is related to the amount and size of interconnecting pore spaces in the rock.

Hydraulic Grade Line: The surface or profile of water flowing in an open channel or a pipe flowing partially full. If a pipe is under pressure, the hydraulic grade line is at the level water would rise to in a small vertical tube connected to the pipe.

Hydraulic Gradient: The slope of the hydraulic grade line. This is the slope of the water surface in an open channel, the slope of the water surface of the groundwater table, or the slope of the water pressure for pipes under pressure.

Hydraulic Staging: Multiple passes of water between electrodes used in an electrodialysis or through a sequence of subsequent membranes or filters used in a reverse osmosis or filtration system to achieve further treatment.

Hydrazine: A liquid compound (H₂NNH₂) used as a strong reducing agent for transition metals and as an oxidation inhibitor for boiler feedwater and cooling water.

Hydrocarbon: An organic compound containing only carbon and hydrogen. Hydrocarbons often occur in petroleum products, natural gas, and coals.

Hydrochloric Acid (HCl): A water-based solution of hydrogen chloride which is a strong, highly corrosive acid. HCl may be used as a regenerant for cation resin deionization systems operated in the hydrogen (H⁺) cycle. HCl may be used as a regenerant for cation resin deionization systems operated in the hydrogen (H+) cycle.

Hydrocyclone: The basic form of most separators which act on the principle of centrifugal force and are used to remove sand and abrasives from well water.

Hydrogen Bond: The weak attraction between a hydrogen atom carrying a partial positive charge and some other atom with a partial negative charge. Hydrogen bonds occur in polar compounds such as water by the attraction of a hydrogen atom of one molecule to two unshared electrons of another molecule. Hydrogen bonds are less than one-tenth as strong as covalent bonds where electrons are actually shared by a pair of atoms, but they significantly affect properties such as the melting point, boiling point, and crystalline structure of substances.

Hydrogen Cycle: A cation exchange cycle (H+ form) in which the cation medium is regenerated with acid and all cations in the water are removed by exchange with hydrogen ions.

Hydrogen Ion Concentration: The concentration of hydrogen ions, reported in moles per liter of solution, used as a measure of the acidity of the solution. Also known as pH.

Hydrogen Peroxide: H₂O₂ A strong disinfectant and oxidizing agent used mostly in dilute water-based solutions. Hydrogen peroxide can be formed in water with a 1948-angstrom mercury-vapor ultraviolet lamp. Hydrogen peroxide may be used in advanced oxidation processes in combination with ozone to encourage the formation of highly reactive hydroxyl radicals; this process is then called the Peroxone process. Also called peroxide.

Hydrogen Sulfide (H2S): A corrosive and flammable gas often found dissolved in well water and often accompanied by iron and low pH values. Hydrogen sulfide develops from decaying organic matter, from sulfate-reducing bacteria, and from petroleum refining. H₂S formation can be catalyzed by a magnesium anode rod in a hot water heater; anaerobic sulfate-reducing bacteria can live in a hot water heater so long as water temperatures are below 140° Fahrenheit, and to produce H₂S the SRB need only a ready source of sulfate ions in the incoming water supply and a ready source of electrons as provided by the water heater’s anode rod. The odor of water with as little as 0.5 milligrams per liter (mg/L) of hydrogen sulfide concentration is detectable by most people. Concentrations less than one mg/L give the water a “musty” or “swampy” odor. Over one mg/L hydrogen sulfide concentration gives water a very disagreeable “rotten egg” odor and makes the water corrosive to plumbing. Generally, hydrogen sulfide levels are less than 10 mg/L, but occasionally amounts of 50 to 75 mg/L are found. At higher pH levels hydrogen sulfides present in the ionized alkaline sulfide (HS_– and S^2-) forms, and at low pH levels it is present in the H₂S gaseous form. At pH 5.0 about 90 percent is present as gaseous H₂S and 10 percent as sulfide. At pH 8 only six percent is present as a gas. Hydrogen sulfide concentrations up to about six mg/L can be removed from water using an oxidizing filter (same as an iron filter). Hydrogen sulfide concentrations exceeding six mg/L can be removed by injecting an oxidizing chemical such as household bleach or potassium permanganate and using a filter. The oxidizing chemical should be thoroughly mixed into the water upstream from a retention tank to provide at least 20 minutes of contact time between the chemical and water. Sulfur particles can then be removed by activated carbon filtration. When potassium permanganate is used a manganese greensand filter is recommended. Other oxidants such as ozone and hydrogen peroxide are also excellent for oxidizing hydrogen sulfide to precipitate sulfur and even to innocuous sulfate.

Hydrogeologic Conditions: Conditions stemming from the interaction of groundwater and the surrounding soil and rock.

Hydrogeologist: A person who studies and works with groundwater.

Hydrogeology: The geology of groundwater, with particular emphasis on the chemistry and movement of water.

Hydrograph: A graph of the rate of runoff plotted against time for a point on a channel.

Hydrologic Cycle: The complete circuit pursued by water in nature, including
1. falling of precipitation (rain, hail, sleet, snow, dew);
2. the journal of fallen water over and through the earth’s surface formations; and
3. eventual evaporation of the water and its return to the atmosphere to again fall as precipitation.

Hydrology: The study of the occurrence, distribution, and circulation of the natural waters of the earth.

Hydrolysate: The product of hydrolysis.

Hydrolysis: A chemical reaction in which a substance reacts with water and becomes a different substance. This involves the ionization of the water molecule as well as splitting of the compound hydrolyzed. An example is the chemical reaction of salt with water which then forms an acid and a base: (NaCl + H2O hydrolyzes to HCl + NaOH).

Hydrometallurgy: The treatment of ores by wet processes as in leaching and accompanying operations, and the technology of separation or recovery of heavy or noble metals from liquid solutions by ion exchange methods.

Hydrometer: A device for measuring the density or specific gravity of liquids. Hydrometers commonly consist of a thin glass or metal tube graduated to indicate either specific gravities or percentages of solution constituents and weighted so that they float upright.

Hydrophilic: Having a strong affinity (liking) for water, and thereby exhibiting the characteristic of absorbing water. Example: Cotton is a hydrophilic fiber. The opposite of hydrophobic.

Hydrophobic: Having a strong aversion (dislike) for water, and thereby exhibiting the characteristic of repelling water. Example: Nylon is a hydrophobic fiber. The opposite of hydrophilic.

Hydropneumatic System: A system that uses both air and water in its operation. An example is the pressure tank which uses an air chamber to maintain pressure in a well system even when the pump is not operating.

Hydrosphere: The pressure at a specific elevation exerted by a body of water at rest or, In the case of groundwater, the pressure at a specific elevation due to the weight of water at higher levels in the same zone of saturation.

Hydrostatic Test: A pressure test procedure in which a vessel or system is filled with water, purged of air, sealed, subjected to water pressure, and then observed and/or tested for leaks, distortions, and/or mechanical failure.

Hydroxide: The negatively charged ion composed of an oxygen and a hydrogen atom (OH-).

Hydroxide Alkalinity: Alkalinity caused by hydroxide ions. SEE ALSO alkalinity.

Hydroxyl: 1. A diatomic functional group in organic molecules, consisting of an atom of hydrogen and an atom of oxygen and indicating an alcohol. The hydroxyl group is covalently bonded to the organic molecule.
2. A highly reactive, diatomic radical consisting of a single atom of hydrogen and a single atom of oxygen, not to be confused with the negatively charged hydroxide anion.

Hygroscopic: Having the characteristic of drawing moisture in from the atmosphere such as silica gel, calcium chloride, or zinc chloride. Sodium chloride (NaCl) is also a hygroscopic substance.

Hyperfiltration: A water treatment process in which desalination of water is achieved by forcing salt solutions, under pressure, through a membrane which generally passes water more readily than salts. An early term for reverse osmosis technology.

Hypochlorination: The application of hypochlorite compounds to water for the purpose of disinfection.

Hypochlorinators: Chlorine pumps, chemical feed pumps, or devices used to dispense chlorine solutions made from hypochlorites such as bleach (sodium hypochlorite) or calcium hypochlorite into the water being treated.

Hypochlorite: The Ocl^– anion, which is the dominant reaction product of chlorine in water at pH greater than 8. Calcium and sodium hypochlorites are commonly used as disinfecting and bleaching agents. High-test hypochlorite is a dry solid, largely calcium hypochlorite, which has excellent stability when kept in dry storage and is used as a disinfectant.

Hypochlorous Acid (HOCl): The dominant reaction product of chlorine in water at pH less than 7.

Hypolimnion: The cold stagnant deep-water layer of a lake.

ICAP: Inductive Coupling Argon Plasma Spectroscopy

ICP: Inductive Coupling Plasma Spectroscopy

ID-50: The dose at which 50 percent of the subjects become infected.

Imhoff Cone: A clear, cone-shaped container marked with graduations. The cone is used to measure the volume of settleable solids in a specific volume (usually one liter) of water.

Immiscible: Not capable of being mixed. For example, oil and water are said to be immiscible.

Impeller: Not easily penetrated. The property of a material or soil that does not allow, or allows only with great difficulty, the movement or passage of water.

Impounded Water: Water which is stored in an artificial man-made basin or dammed ravine by diverting flowing streams or collecting rainfall runoff, as in a reservoir.

In Situ: In place, the original location, in the natural environment.

In Vitro Studies: Studies of chemical effects conducted in tissues, cells, or subcellular extracts from an organism (i.e., not in the living organism).

In Vitrov: Literally, “in glass.” A laboratory experiment performed in a test tube or other vessel.

In Vivo: Within a living organism; a laboratory experiment performed in which the substance under study is inserted into a living organism.

In Vivo Studies: Studies of chemical effects conducted in intact living organisms.

In-Stream Uses: Water uses that can be carried out without removing the water from its source, as in navigation and recreation.

In-line Filtration: The addition of chemical coagulants directly to the filter inlet pipe. The chemicals are mixed by the flowing water. Flocculation and sedimentation facilities are eliminated. This pretreatment method is commonly used in pressure filter installation.

In-parallel Flow: A piping arrangement which directs separate streams through two or more units of a treatment system in a balanced manner, with equal flow to each device, so that a higher total flow rate than that from a single unit can be achieved.

In-series Flow: A piping arrangement in which the entire effluent flow from one unit of a water treatment system is fed to a second succeeding unit. This arrangement forces the water through multiple treatment units and achieves greater reduction of contaminants than can be achieved by a single pass of water through a single unit.

Inactivate: To make inactive or inert, esp. the alteration or destruction of a biologically active agent such as pathogenic microorganisms or antigens so as to render them harmless.

Incidence of Tumors: Percentage of animals with tumors.

Incubation Period: The time between initial contact with an infectious agent and the appearance of the first sign or symptom of disease.

Indicator: (Chemical) A chemical material or solution which can be used to show (usually by color change or depth of color) the endpoint of a chemical reaction or chemical concentration. Examples are litmus; orthotolidine reagent.
(Instrument) A device which indicates the result of a measurement. Most indicators in the water treatment field use either a fixed scale and movable indicator (pointer), such as a pressure gauge, or a movable scale and movable indicator like those used on a circular-flow recording chart. Also called a receiver.

Induced Infiltration: An emission spectroscopy technique for chemical analysis in which the elements that are to be measured are introduced into a high temperature (6,000 to 8,000 degrees C) argon plasma and, thereby, converted into atomic vapor. Emission spectroscopy is used to identify and quantify the elements. The high temperature of the plasma limits interferences and ICP has broader application (e.g., for waste water analyses) than atomic absorption (AA) spectroscopy for metals analyses, but it has lower detection power.

Inert Media: Synthetic resin beads or water treatment materials that are nonreactive. Inert media are used as a neutral nonreactive layer to more effectively separate the cation resin from the anion resin in mixed bed deionizers in order to regenerate each separately.

Infiltration: The movement of water into rocks or soil through interstitial pores, small cracks, or crevices in the soil or rock.

Infiltration Gallery: A subsurface groundwater collection system, typically shallow in depth, constructed with open-jointed or perforated pipes that discharge collected water into a water-tight chamber. From this chamber, the water is pumped to treatment facilities and into the distribution system. Infiltration galleries are usually located close to streams or ponds and may be under the direct influence of surface water.

Infiltration Rate: Quantity of water (usually measured in inches) that will enter a particular type of soil per unit time (usually one hour).

Influent: The stream of water to be treated as it flows into any kind of water treatment unit or device, such as hard water into a softener or turbid water into a filter.

Ingestion: Type of exposure in which a substance is introduced through the mouth.

Inhalation: Type of exposure in which a substance is introduced through the lungs.

Inhibitor: Any chemical substance that is added to a water supply (or solution of any kind) which interferes with (“inhibits”) a chemical reaction. For example, inhibitors are sometimes used to help prevent precipitation or corrosion.

Initial Compliance Period: The first full three-year compliance period which begins at least 18 months after promulgation.

Inorganic Matter: Chemical substances which do not arise from the process of living growth, are composed of matter other than plant or animal matter, and don’t contain hydrocarbons or compounds of basically carbon structure.

Input Horsepower: The total power used in operating a pump and motor. Input HP = (brake HP)(100%) / motor efficiency, %

Insecticide: Any substance or chemical formulated to kill or control insects.

Installation: The connecting or setting up and startup operations of any water treatment system. The term also refers to complete assembly of piping, valves, drain line, pumps, meters, and controls by which the equipment is connected into the water supply system.

Integrated Exposure Assessment: A summation over time, in all media, of the magnitude of exposure to a toxic chemical.

Interface: The surface which forms a common boundary between two spaces or two parts of matter, such as the surface boundary formed between oil and water. The term “interface” is often used to refer to the space between two different ion exchange resins in a mixed bed or to the resin surface at the regeneration grid in a mixed bed deionization system.

Interflow: Lateral movement of water in the upper layer of soil.

Interlock: An electrical control unit which delays the regeneration of one ion exchange unit while another unit is in the regeneration cycle.

Intermittent Flow: The interrupted patterns of water usage which occur in the home or in commercial businesses opposed to the steady constant flow patterns common in industry, such as in factories. This term may also be used to refer to “on-off” flow patterns of water through treatment units specified in testing standards to simulate customer water use patterns.

Internal Friction: Friction within a fluid (water) due to cohesive forces.

Internal Water Treatment: Water treatment processes involving the addition of chemicals to the makeup water used in steam generation for boiler operations. Chemicals are often added to prevent scale buildup or corrosive pitting of metal in boiler system components.

Interspecies Extrapolation Model: Model used to extrapolate from results observed in laboratory animals to humans.

Interstate Carrier: Any vehicle or transport which conveys passengers in interstate commerce.

Interstices: The pores or other spaces which are not occupied by solid matter and may be found between filter medium particles, ion exchange resin beads, or other similar treatment media. Interstices may be occupied by air, water, or other gaseous or liquid material. This term is also used to refer to similar spaces between natural soil or rock particles; and spaces between atoms or molecules in solids.

Invert: The lowest point of the channel inside a pipe, conduit, or canal.

Iodine: (I₂) A nonmetallic element which is the heaviest and least reactive of the naturally-occurring halogens. It may be used for disinfection. In both its liquid and vapor forms, iodine is readily adsorbed by activated carbon.

Iodine Number: A measure of the ability of an activated carbon product to adsorb substances with low molecular weights. The iodine number of a carbon is equal to the milligrams (mg) of iodine that can be adsorbed on one gram of activated carbon.

Ion: An atom or radical (group of atoms such as SO₄^2- which carries an electrical charge as the result of having lost or gained electrons. Positively-charged ions are called cations; negatively charged ions are called anions. An ion often has entirely different properties than the element (atom) from which it was formed.

Ion Exchange: A reversible chemical process in which ions from an insoluble permanent solid medium (the “ion exchanger”–usually a resin) are exchanged for ions in a solution or fluid mixture surrounding the insoluble medium. The superficial physical structure of the solid is not affected. The direction of the exchange depends upon the selective attraction of the ion exchanger resin for the certain ions present and the concentrations of the ions in the solution. Both cation and anion exchange are used in water conditioning. Cation exchange is commonly used for water softening.

Ion Exchange Membrane: A water-tight and electrically-conductive membrane which is either ion exchange resin cast in sheet form or powdered ion exchange resin laminated to a membrane fabric. Both anion and cation ion exchange membranes are used in electrodialysis treatment systems.

Ion Exchanger: A permanent insoluble material (usually a synthetic resin) which contains ions that will exchange reversibly with other ions in a surrounding solution. Both cation and anion exchangers are used in water conditioning. The volume of an ion exchanger is measured in cubic feet (or cubic liters) of exchanger after the exchanger bed has been backwashed and drained and has settled into place.

Ionic Concentration: A measure of the concentration of any ion in solution, usually expressed in moles per liter.

Ionic Constant: A measure in absolute units of the extent to which a chemical compound or substance in solution will dissociate into ions.

Ionic Weight: The weight of an ion as determined by the sum of the atomic weights of its components.

Ionization: The process in which a chemical combination breaks up into simpler electrically-charged components (individual atoms or groups of atoms) called ions. The ionization process is related to the gaining or losing of electrons causing the atoms or group of atoms to become electrically charged. The term “ionization” is sometimes used as if it had the same meaning as dissociation.

Iron (Fe): A very common element often present in groundwater in amounts ranging from 0.01 to 10.0 ppm (mg/L). Iron may be found in three forms: In soluble form such as in ferrous bicarbonate; Bound with a soluble organic compound; and As suspended ferric iron particles. Iron above 0.3 mg/L is objectionable in water because of staining of laundry and plumbing fixtures caused by the oxidation and precipitation of ferric hydroxide and/or ferric oxide (ferric iron) into small solid iron particles. Iron can also give a metallic or distorted flavor to beverages. Iron also occurs in water as ferric iron.

Iron Bacteria: Bacteria which thrive on iron and are able to actually use ferrous iron (as found in water or steel pipes) in their metabolic processes, to incorporate ferric iron in their cell structure, and to deposit gelatinous ferric hydroxide iron compounds in their life processes. Iron bacteria are found in several varieties including Crenothrix, Lepothrix, and Gallionella. Iron bacteria can cause staining, plugging, and taste and odor problems in a water system.

Iron Fouling: The accumulation of iron on or within an ion exchange resin bed or filter medium in such amounts that the capacity of the medium is reduced.

Irreversible Effect: Effect characterized by the inability of the body to partially or fully repair injury caused by a toxic agent.

Isotherm: The measurement which represents the relationship between the mass of the substance adsorbed (adsorbate) at a given temperature and the mass of the adsorbent.

Isotope: One of two or more atoms or elements which have the same atomic number (occupy the same position in the periodic table) but which differ in other respects such as atomic weight and number of neutrons in the nucleus.

Jackson Turbidity Unit (JTU): A formerly-used measurement of the turbidity in a water sample. This has been replaced by the nephelometric turbidity unit.

Jar Test: A laboratory procedure that simulates a water treatment plant’s coagulation/flocculation units with differing chemical doses and also energy of rapid mix, energy of slow mix, and settling time. The purpose of this procedure is to estimate the minimum or ideal coagulant dose required to achieve certain water quality goals. Samples of water to be treated are commonly placed in six jars. Various amounts of chemicals are added to each jar, stirred, and the settling of solids is observed. The dose of chemicals that provides satisfactory settling removal of turbidity and/or color is the dose used to treat the water being taken into the plant at that time. When evaluating the results of a jar test, the operator should also consider the floc quality in the flocculation area and the floc loading on the filter.

Jet (Ejector) Pump: A combined centrifugal and ejector pump. In a jet pump, a portion of the discharge water from the centrifugal pump is diverted through a nozzle and venturi tube. A pressure zone lower than that of the surrounding area is created by the velocity of water flowing through the venturi tube; therefore, water from the source (the well) flows into this area of reduced pressure. The velocity of the water from the nozzle pushes the water through the pipe toward the surface where the centrifugal pump can lift it by suction. The centrifugal pump then forces the water into the water plumbing system.

Jetted Well: A shallow well constructed by a high-velocity stream of water directed downward into the ground.

Jogging: The frequent starting and stopping of an electric motor.

Joule: A measure of energy, work, or quantity of heat. One joule is the work done when the point of application of a force of one newton is displaced a distance of one meter in the direction of force. The absolute unit of work-energy equal to 10⁷ ergs or about 0.7736 foot-pounds or 0.2389 calories. One joule is the work done when the point of application of a force of one newton is displaced a distance of one meter in the direction of force. The absolute unit of work-energy equal to 10⁷ ergs or about 0.7736 foot-pounds or 0.2389 calories.

KDF: The trade name for a patened medium composed of high purity copper and zinc granules. KDF is capable of removing chlorine, soluble heavy metals, and other inorganic contaminents from water through the chemical reduction/oxidation (redox) process.

KYNAR: Trade name for polyvinylidene fluoride.

Kation: The older German spelling of cation.

Kelvin Scale: A temperature scale which measures from absolute zero (-273.15 degrees Celsius) in Kelvins which are equivalent to Celsius degrees in magnitude. Kelvins = Celsius degrees + 273.15.

Kilo: The metric prefix used to mean “1000” of some unit of measure: a kilometer is 1,000 meters; a kilogram is 1,000 grams. The term kilo is sometimes used to mean kilogram.

Kilograin: 1,000 grains

Kilogram: 1,000 grams

Kiloliter: 1,000 liters (264.18 U.S. gallons) or one cubic meter.

Kilowatt-Hour: The unit of electric energy or work equal to that done by one kilowatt in one hour. Equal to 1,000 watt-hours.

Kinetic Energy: Energy possessed by a moving body of matter, such as water, as a result of its motion.

Kinetics: The study of the relationships between temperature and the motion and velocity of very small particles. Kinetic relationships influence the rate of change in a chemical or physical system and are used particularly to describe the dynamics and rate of ion exchange reactions.

Kjeldahl Nitrogen: Nitrogen in the form of organic proteins or their decomposition product ammonia, as measured by the Kjeldahl Method.

kPa: Kilopascal

L/d: liters per day.

L/min.: liters per minute.

LAS: linear alkylate sulfonate.

LC50: The concentration of a chemical in air or water which is expected to cause death in 50 percent of test animals living in the air or water.

LD50: The dose of a chemical taken by mouth or absorbed by the skin which is expected to cause death in 50 percent of the test animals so treated.

LOAEL: Lowest-observed-adverse-effect level; the lowest dose in an experiment which produced an observable adverse effect.

Laminar Flow: The movement of fluid in a particular direction in smooth, continuous, nonturbulent parallel layers which do not mix with each other.

Landfill: Facility in which solid waste from municipal and/or industrial sources is disposed; sanitary landfills are those that are operated in accordance with environmental protection standards.

Langelier Saturation Index: A calculated number used to predict the calcium carbonate (CaCO₃) stability of a water; that is, whether a water will precipitate, dissolve, or be in equilibrium with, calcium carbonate. It is sometimes erroneously assumed that any water that tends to dissolve CaCO₃ is automatically corrosive. Langelier saturation index = pH – pH_swhere pH = actual pH of the water, and pH_s = pH at which the water having the same alkalinity and calcium content is just saturated with calcium carbonate.

Large Public Water System: A public water system that serves more than 50,000 persons.

Latency: Time from the first exposure to a chemical until the appearance of a toxic effect.

Latent Heat: The amount of heat released or absorbed when a substance changes its physical phase with no change in temperature. For example, the heat absorbed from surroundings when ice melts into liquid water at the freezing point or the heat released when a gas (steam) condenses into liquid water. The loss or gain of latent heat is not reflected in the temperature of the melting ice or the condensing water.

Laundering weir: Sedimentation basin overflow weir. A plate with V-notches along the top to assure a uniform flow rate and avoid short-circuiting.

Launders: Sedimentation basin and filter discharge channels, consisting of overflow weir plates (in sedimentation basins) and conveying troughs.

Laundry Detergent: A product containing a surfactant and other ingredients, formulated to clean and care for the many different fabrics in the family wash. Next to the surfactant, a builder is an important ingredient in formulated laundry detergents. Builders have a number of functions, principally inactivation of water hardness, which interferes with good cleaning. Built detergent types include granules and liquids. Some liquid detergents are unbuilt, containing surfactants that are relatively insensitive to water hardness. Other customary ingredients of laundry detergents include antiredeposition agents, corrosion inhibitors, fluorescent whitening agents, colorants, fragrance, and processing aids. Optional ingredients include suds control agents, bleach, borax, enzymes, bluing, fabric softener, and soil release agent. Some laundry detergents are denser or more concentrated than others. Density or concentration influences the amount of product recommended for the wash. Detergents also vary in sudsing characteristics, ranging from high to low suds levels. Different suds levels are provided for reasons of compatibility with machine design and to satisfy consumer preferences. Depending on the presence of other ingredients in the laundry detergent formulation, some products offer special benefits in addition to the expected cleaning. Thus, certain laundry detergents are especially effective at lower washing temperatures; others provide additional fabric care benefits, such as softening, static control, and wrinkle reduction.

Layered Bed: As relates to filtration, a multimedia filter bed containing, in the same vessel, several different filter media (such as anthracite, sand, and garnet) with specific gravities which differ enough to maintain different layers even after backwashing. layered bed In ion exchange, a single exchange bed made up of two or more resins which have bead sizes and densities different enough to maintain layers after backwashing and which can be regenerated with the same regenerant. For example, a layered bed may have a mixed bed of anion resin on top and cation resin below that is regenerated by salt brine solution.

Leach: To dissolve out by the action of a percolating liquid.

Leach Field: The area where the effluent from a septic tank system is distributed by horizontal underground piping designed to aid in the process of natural leaching and percolation through the soil.

Leachate: Water which has percolated or filtered through soil, a filter medium, or other substance containing soluble substances so that it now contains certain amounts of these substances in solution.

Leaching: The process by which soluble substances are dissolved and transported down through the soil by recharge.

Lead (Pb): A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations.

Lead Service Line: A service line made of lead which connects the water main to the building inlet and any lead pigtail, gooseneck, or other fitting which is connected to such lead line.

Leakage: As relates to ion exchange, the presence in the effluent of the type of ions, present in the feedwater to be treated, which the ion exchange process was supposed to remove. Incomplete removal of the ions may be caused by incomplete regeneration, excessive service rates, low temperatures, high concentrations of sodium, or interfering TDS in the water being treated, and other factors. Leakage is also referred to as slippage.

Legionella: Over 26 species of bacteria, such as Legionella pneumophila, which can cause the pneumonia-like illness called “Legionnaires’ Disease” (after the American Legion convention at which the disease first drew attention). These bacteria are known to thrive at about 100 degrees F and are believed to live in infected humidifiers, cooling tower water, and shower rooms. Infection is by inhalation.

Lesion: A pathological or traumatic discontinuity of tissue or loss of function of a part.

Lethal: Deadly; fatal.

Level Controls: A float device (or pressure switch) which senses changes in a measured variable and opens or closes a switch in response to that change. In its simplest form, this control might be a floating ball connected mechanically to a switch or valve such as is used to stop water flow into a toilet when the tank is full.

Lifetime Exposure: Total amount of exposure to a substance that a human would receive in a lifetime (usually assumed to be 70 years).

Lift-and-Turn Valve: A master control valve for operating and manually regenerating softeners and filters.

Lime (CaO): A calcined chemical material, calcium oxide. Lime is used in lime and in lime and soda ash water treatment, but must first be slaked to calcium hydroxide [Ca(OH)2]. Lime is also called burnt lime; calyx; fluxing lime; quicklime; unslaked lime.

Lime Scale: Hard water scale formed in pipes and vessels (generally more severe on the hot water side) containing a high percentage of calcium carbonate (CaCO₃) or magnesium carbonate (MgCO₃).

Lime Soap: The insoluble calcium and magnesium salts formed from the fatty acid portion of soap when it combines with minerals in hard water; it is commonly referred to as soap curd. The use of the word lime in this term may come from the fact that limestone areas generally foster hard water, or from the fact that the words lime and calcium are closely associated. Calcium and magnesium fatty acid salts are highly insoluble and precipitate immediately on formation. Since they tend to agglomerate (cluster together), they form curd-like masses. They also tend to adhere to surfaces, thus causing filming or deposits, such as bathtub ring. The problems lime soap causes spurred the development of mechanical water softeners, packaged water softeners, and the technology leading to new surfactants and builders and detergent products based on them.

Lime Soda Ash Softening: A water treatment process done to further reduce the hardness of lime treated water using soda ash (Na₂CO₃) to raise the pH of the feed stream and precipitate the hardness which is then filtered out. The residual hardness is typically 4-5 gpg depending on the treatment design. It does not produce soft water. SEE ALSO hot lime-soda softening, lime softening.

Lime Softening: A water treatment process done to reduce the hardness of hard water that is often used by municipalities and larger industrial water users. Slaked lime [Ca(OH)₂] is added to the water to precipitate the hardness ions as calcium and magnesium carbonate or hydroxide. The precipitate is then filtered. The residual hardness may exceed 6-10 gpg depending on the treatment design. This does not product soft water. SEE ALSO hot lime softening; lime-soda ash softening.

Limestone: A sedimentary rock composed mostly of calcium carbonate (CaCO₃) and usually some magnesium carbonate (MgCO₃).

Limit Stops: Several types of diaphragm valves which have adjustments used to control flow rates during various processes (backwash, fast rinse, or brine dilution) when brine is pumped in during batch regeneration of resin for portable ion exchange tanks.

Limnetic Community: The area of open water in a fresh water lake providing the habitat for fish, phytoplankton, and zooplankton.

Limnology: The scientific study of conditions in freshwater lakes, ponds, and streams.

Lindane: A pesticide that causes adverse health effects in domestic water supplies and also is toxic to freshwater and marine aquatic life.

Linear Alkyl Sulfonate (LAS): Readily biodegradable form of alkylbenzene sulfonate surfactant. This is the workhorse of the detergent industry, with sodium dodecylbenzene sulfonate being the most important single type. It is distinguished from an earlier form of alkylbenzene sulfonate, termed ABS, but is a linear (straight chain) structure, which provides its good biodegradation properties. All LAS surfactants are anionic and high sudsing, but their sudsing may be controlled by formulation.

Linearity: How closely an instrument measures actual values of a variable through its effective range; a measure used to determine the accuracy of an instrument.

Linearized multistage model: Derivation of the multistage model, where the data are assumed to be linear at low doses.

Liquefication: The transformation to the liquid state. This term is more commonly used to refer to the changing of gases to liquids than to refer to the melting of solids to liquids.

Liquid Chromatography: Chromatography in which the mobile phase is a liquid (i.e., the sample is introduced into a liquid solvent which then flows through a fractionating column and to a detector). Separation of the sample components is accomplished via three different modes:
1. liquid/ liquid, in which the relative solubilities of sample components in two immiscible fluids (one of which is usually water) create separation;
2. liquid/solid, in which the relative adsorption of sample components on a solid adsorptive medium surface creates separation; and 3. molecular-size, in which separations are created because of the variations in effective molecular dimensions of the sample components in solution.

Liquor: A solution of one or more chemical substances (gas, solid, or liquid) in water.

Liter: The basic international metric unit of volume measure. One liter equals 33.82 fluid ounces; 3.785 liters equals one U.S. gallon. One liter of water weighs 1,000 grams at 4 degrees Celsius at standard atmospheric pressure.

Littoral Zone: 1. That portion of a body of fresh water extending from the shoreline lakeward to the limit of occupancy of rooted plants.
2. The strip of land along the shoreline between the high and low water levels.

Loading: The quantity of a substance entering the environment (soil, water, or air).

Lodestone: SEE magnetite

Logarithm: The exponent that indicates the power to which a number must be raised to produce a given number. Also abbreviated to “log.”

Longitudinal Flow: A flow pattern in which water travels from the bottom to top (or vice versa) in either a cartridge-type or loose media tank-type filtration system. The advantages are greater contact time, higher unit capacity, more complete utilization of medium, and more uniform water quality. Also called axial flow.

Loop: 1. The plumbing network designed to continuously circulate ultrapure grade water in high purity water systems between storage and disinfection modes to maintain microbiological cleanliness.
2. A plumbing connection used to bypass water around a location designed for installation of a water treatment system or used when the treatment system is out of service for any reason.

Loose Media Filters: Those filter units which have medium products positioned in a filter bed such that the individual medium grains or particles can be repositioned or lifted relative to each other with the flow of water or backwash water; as compared to permanently fixed bed media filter or a fixed solid block of filter media.

Lyse: To undergo lysis

Lysimeter: A device for measuring the percolation and drainage of water through soils.

Lysis: A process of disintegration or destruction of bacteria or microbiological cells by chemically breaking them down into their component parts.

loose medium (media): Filter or ion exchange media (in a tank or bed) which can be expanded during backwashing and rinsing. “Loose” is used to differentiate from a contained or “fixed medium” in a tank or the fixed or compressed media layer in a cartridge filter.

lye: SEE sodium hydroxide

M alkalinity: SEE alkalinity tests.

MBAS Methylene-Blue- Active Substances: These substances are used in surfactants or detergents.

MCL: Maximum Contaminant Level.

MCLG: Maximum Contaminant Level Goal.

MPN: Most probable number.

MTD: Maximum tolerated dose, the dose that an animal species can tolerate for a major portion of its lifetime without significant impairment or toxic effect other than carcinogenicity.

Macroporous Resin: A special grade of ion exchange resins which have large pores and a higher resistance to oxidation and organic fouling. They were developed to provide increased surface area for reactions with organic matter with large molecular weights. Macroporous resins are manufactured with a third ingredient that is soluble in the styrene and divinylbenzene monomers but becomes insoluble in the polymer structure as it is formed. The third ingredient is then removed from the resin structure by a solvent leaving a resin bead that has both a continuous resin phase and a continuous pore phase, resulting in considerable net porosity and internal surface area. Macroporous resins, which are produced in both anion and cation versions, contain higher levels (12% or more) of divinylbenzene cross-linking, which reduces the swelling of the polymer resin in water. Also called macroreticular resin.

Macrorecticular resin: SEE macroporous resin.

Macroscopic Organisms: Organisms big enough to be seen by the eye without the aid of a microscope.

Macroscopic Organisms: Organisms big enough to be seen by the eye without the aid of a microscope.

Magnesia: Magnesium oxide (MgO) that has been specially processed. Magnesia water treatment can be used for pH modification of water.

Magnesium (Mg): One of the elements that make up the earth’s crust as part of many rock-forming minerals such as dolomite. Magnesium and calcium dissolved in water constitute hardness. The presence of magnesium in water contributes to the formation of scale and the insoluble soap curds which identify hard water.

Magnetite: (Fe₃O₄) A black magnetic oxide of iron that is extremely dense and used as a coagulant and filter medium in water treatment. Magnetite is readily recognized by its strong attraction to magnets. Also called lodestone.

Makeup Water: Treated water added to the water loop of a boiler circuit or cooling tower to make up for the water lost by steam leaks or evaporation.

Malignant: Very dangerous or virulent, causing or likely to cause death.

Man-made beta particle and photon emitters: All radionuclides emitting beta particles and/or photons listed in Maximum Permissible Body Burdens and Maximum Permissible Concentration of Radionuclides in Air or Water for Occupation Exposure, NBS Handbook 69, except the daughter products of thorium-232, uranium-235, and uranium-238.

Managerial Controls: Methods of nonpoint source pollution control that are derived from managerial decisions, such as changes in application times or rates for agrochemicals.

Manganese (Mn): An element sometimes found dissolved in groundwater, usually in combination with – but in lower concentrations than- iron. Manganese is noticeable because in concentrations above 0.05 mg/L it causes black staining of laundry and plumbing fixtures. Important ores of manganese are pyrolusite, manganite, psilomelane, and rhodochrosite.

Manganese Dioxide: (MnO₂) A dark brown or gray-black insoluble compound found in nature as pyrolusite, made synthetically, and used as an oxidizing agent in water treatment and as a starting material for permanganate compounds such as potassium permanganate.

Manganese Dioxide-Coated Pumicite: An oxidizing catalyst medium used to remove iron and manganese. The manganese is sacrificial.

Manganese Greensand: Greensand which has been processed to incorporate the higher oxides of manganese into its pores and onto its surface. Manganese greensand has a mild oxidizing power and is often used in the oxidation, precipitation, and removal of iron, manganese, and/or hydrogen sulfide. It is regenerated by solutions of potassium permanganate (KMnO₄).

Manganese Zeolite: A synthetic gel zeolite (sodium alumino silicate) which has been converted to the manganese form by the same process as manganese greensand and is used for the same treatment applications as manganese greensand. Manganese zeolite is also regenerated with potassium permanganate (KMnO₄).

Manganite [MnO(OH)]: A form of manganese ore, consisting of manganic hydroxide, which is used in filters designed to reduce iron, manganese, and/or hydrogen sulfide and requires a very high backwash rate because of its very high density (specific gravity 4.3). Similar to pyrolusite.

Manifold: A large pipe to which a series of smaller pipes are connected. Also called a header.

Manometer: An instrument for measuring pressure. Usually, a manometer is a glass tube filled with a liquid that is used to measure the difference in pressure across a flow-measuring device such as an orifice or Venturi meter. The instrument used to measure blood pressure is a type of manometer.

Margin of Safety (MOS): Maximum amount of exposure producing no measurable effect in animals (or studied humans) divided by the actual amount of human exposure in a population.

Marine Salt: An early chemical name for salt, partly because of its source.

Mass Spectrometry (MS): A method of chemical analysis, used as a detector in gas chromatography, for example, in which the compounds emerging from the chromatograph are fragmented and ionized by bombardment with a beam of electrons. An electromagnetic field separates the ions according to their individual mass-to-charge ratios into a characteristic mass spectrum of the molecule. A computer analyzes the spectra and makes it possible to identify molecules even in cases of poor separation on the chromatography column, hence the advantage of mass spectrometry compared to selective chromatograph detectors.

Mass Transfer: The movement of molecules of a substance to and across an interface from one phase to another. For example, the amount (mass) of ozone that transfers from air, across the air-water interface and into water; or the amount of organic material that transfers from water to a solid adsorption surface. The rate and amount of mass transfer can be increased by:
1. enlarging the interface boundary by increasing the area of the interface or by rapid renewal or clearance of the interface;
2. increasing the concentration difference (which is the driving force) across the interface boundary, and/or;
3. increasing the length of time (contact time) the interface boundary exists.

Mass Transfer Zone: The region in a treatment unit where the concentration of the contaminant(s) of interest in the water or fluid decreases from influent concentration(s) to the lowest detectable concentration(s). For example, the region of an adsorption column in which adsorption is taking place.

Mathematical Model: Model used during risk assessment to perform extrapolations.

Maximum Total Trihalomethane Potential (MTTP): The maximum concentration of total trihalomethanes produced in a given water containing a disinfectant residual, after seven days at 25 degrees C or above.

Maximum contaminant level (MCL): SEE drinking water standards

Maximum contaminant level goals (MCLGs): SEE drinking water standards

Mean Particle Diameter: The weighted average particle size, in millimeters, of the media particles or beads in a filter or ion exchange bed. Mean particle diameter is computed by multiplying the percent retained in a size fraction by the respective mean sieve openings, summing these values and dividing by 100.

Measured Variable: A characteristic or component part that is sensed and quantified (reduced to a reading of some kind) by a primary element or sensor.

Mechanical Claim: A manufacturer’s claim that is based on reduction in concentration of an unwanted contaminant by a physical means. An example would include size exclusion.

Mechanical Filter: SEE barrier filter.

Mechanical Joint: A flexible device that joins pipes or fittings together by the use of lugs and bolts.

Media: A selected group of materials used in filters and filter devices to form barriers to the passage of certain solids or molecules which are suspended or dissolved in water. It is also common to use the term media to refer to ion exchange resin products. Media is the plural form of medium and refers to more than one type of barrier material.

Median: A statistical term representing the middle value of a series of numbers when the numbers are arranged in order of their numerical quantity or value. Equal numbers of data points can be found that are greater than or less than the median. For example, in the sequence 1,3,4,7,8,10,12, the median is 7.

Medium: The singular form of media.

Medium Size Public Water System: A public water system that serves greater than 3,300 and less than or equal to 50,000 persons.

Meg: Abbreviation for megohm. Meg means one million.

Mega: 1. A prefix meaning large;
2. A million of; or multiplied by one million.

Membrane: A thin sheet or surface film, either natural or man-made, of microporous structure that performs as an efficient filter of particles down to the size range of chemical molecules and ions. Such membranes are termed “semipermeable” because some substances will pass through, but others will not. Usually small ions, water, solvents, gases, and other very small molecules can pass through a membrane, but other ions and macromolecules such as proteins and colloids are barred from passage. Man-made (synthetic) membranes are highly engineered polymer films about 100 angstroms thick and with controlled distributions of pores ranging from 5 to 5,000 angstroms in diameter. Membranes are used in reverse osmosis, electrodialysis, nanofiltration, ultrafiltration, and as pleated final filter cartridges in water treatment. SEE ALSO cellulose acetate (CA); cellulose triacetate (CTA); charged polysulfone membrane.

Membrane Filtration: A laboratory analytical technique for the quantitative and qualitative analysis of bacterial or particulate matter in a water sample. Upon filtering through a membrane of specified pore size (e.g. 0.45 micron), bacteria and particles of larger size are separated from the water sample and are retained on the filter. Then by incubation with a suitable nutrient and temperature, the captured bacteria will grow to visible colonies that can be counted; or by careful weighing, the amount of suspended particulate solids can be determined in the water sample.

Membrane softening: SEE nanofiltration

Membrane, ion exchange: SEE ion exchange membrane

Meniscus: The curved top of a column of liquid (water, oil, mercury) in a small tube. When the liquid wets the sides of the container (as with water), the curve forms a valley. When the confining sides are not wetted (as with mercury), the curve forms a hill or upward bulge.

Mercury vapor ultraviolet light: The ultraviolet light given off as the result of an electron flow through an ionized mercury vapor between electrodes in an ultraviolet lamp. The mercury vapor UV wavelength, which is most destructive to microorganisms in water, is 254 nanometers.

Mesh Size: Mesh is the number of openings in a square inch of a screen or sieve. It is equal to the square of the number of strands of metal or plastic screening per lineal inch. Ion exchange and filter media are graded by U.S. mesh or screen sizes according to the percent of the medium’s particles that will pass through or be retained on certain mesh screens. Standard U.S. mesh screen #16 equates to a 1.19 millimeter particle diameter; mesh size #40 is 0.42 millimeters. Therefore, media rated as 95 percent -16+40 U.S. mesh would have 95 percent or more of the media particles with sizes between 0.42 and 1.19 mm in diameter.

Mesotrophic: Reservoirs and lakes which contain moderate quantities of nutrients and are moderately productive in terms of aquatic animal and plant life.

Metabolism: The sum of the chemical reactions occurring within a cell or a whole organism; includes the energy-releasing breakdown of molecules (catabolism) and the synthesis of new molecules (anabolism).

Metabolite: Any product of metabolism, especially a transformed chemical.

Metalimnion: The middle layer in a thermally stratified lake or reservoir. In this layer, there is a rapid decrease in temperatures with depth. Also called the thermocline.

Metastatic: Pertaining to the transfer of disease from one organ or part to another not directly connected with it.

Methane: A colorless, odorless, flammable gas consisting of the hydrocarbon (CH₄) and resulting from the decay of vegetable matter or manure due to the action of anaerobic bacteria in swampy land, closed landfills, or sewage disposal plants. Methane is also known as biogas and it is called swamp gas when produced in marshy land. Coal miners know methane as one of the main components of fire-damp and also of coal-gas. Methane dissolved in water gives the water a milky cast, and since it is flammable, methane must be safely aerated and vented to the atmosphere during removal.

Methemoglobinemia: A serious condition, found mostly in young infants under six months of age (or newborn animals), in which the oxygen-carrying capacity of the blood is reduced as a result of a reaction with nitrite (NO₂^–), which changes the healthy hemoglobin to an inactive methemoglobin form. As a result of the higher pH conditions in the gastrointestinal tract of infants and newborn animals, nitrate (NO₃^–), which is consumed in food or water, can be transformed into nitrite more readily than would occur with adults.

Methoxychlor: A pesticide which causes adverse health effects in domestic water supplies and is also toxic to freshwater and marine aquatic life. The chemical name for methoxychlor is 2,2-bis (p-methoxyphenol)-1,1,1-trichloroethane.

Methyl Orange: An acid-base indicator that turns red in a solution below three on the pH scale and yellow between pH of 4.4 and 7.0.

Methyl Orange Alkalinity: A measure of the total alkalinity in a water sample. The alkalinity is measured by the amount of standard sulfuric acid required to lower the pH of the water to a pH level of 4.5, as indicated by the change in color of methyl orange from orange to pink. Methyl orange alkalinity is expressed as milligrams per liter equivalent calcium carbonate.

Methyl Tertiary Butyl Ether (MTBE): Since MTBE was incorporated in the mid-1980s into gasoline mixtures as an antiknock replacement for aromatics and as an “oxygenator” to reduce carbon monoxide emissions, it has increasingly appeared in groundwater due to spills of reformulated gasoline and leaking underground storage tanks at gasoline stations. It is highly water soluble and its appearance typically marks the leading front of a contamination plume. The molecular weight of MTBE (C₅H₁₂O) is 88.15. In terms of noncarcinogenic effects, it has low oral toxicity, but at the gasoline pump and in the automobile, symptoms such as airway and eye irritation have been reported. In water, MTBE has a noticeable odor at 20 to 40 µg/L (U.S. Environmental Protection Agency, 1997). Though MTBE is not mutagenic/genotoxic, exposure to high levels by inhalation (8000 ppm) or by ingestion (1000 mg/kg) was associated with the development of lymphoma and leukemia, as well as liver, renal, and testicular cancers in rodents (Burleigh-Flayer et al., 1992; Belpoggi et al., 1995). The relevance of these cancers to human health is not clear, but “weight of evidence suggests that MTBE is an animal carcinogen.” “Concentrations in the range of 20 to 40 µg/L are about 20,000 to 100,000 (or more) times lower than the range of exposure levels in which cancer or non-cancer effects were observed in rodent tests.” (U.S. Environmental Protection Agency, 1997). Thus, the USEPA says “protection of the water source from unpleasant taste and odor will also protect consumers from potential (MTBE) health effects.” MTBE is adsorbed onto activated carbon similar to chloroform, but with a use rate of 2-3 times that of chloroform, i.e., the life of the activated carbon may be only 1/2 to 1/3 of that for chloroform when MTBE will begin to break through. For concentrations of MTBE greater than 100 µg/L or parts per billion, pretreatment with an atmospheric air stripping system with repressurization is recommended prior to activated carbon adsorption.

Methylene-Blue Active Substances (MBAS): These substances are used in surfactants or detergents.

Mho: (Backward spelling of ohm) A unit of conductance equal to the reciprocal of the ohm. Also called siemens.

Microbial Growth: The activity and growth of microorganisms such as bacteria, algae, diatoms, plankton, and fungi.

Microbiocide: Similar to biocide but does not necessarily kill macroscopic and multicelled organisms.

Microbiologically unsafe water: Water that (1) is known to contain disease-causing bacteria, viruses, protozoa or other disease-causing microbiological agents, or (2) shows a positive test for an indicator organism such as coliform, fecal coliform, or E. coli bacteria, or (3) is determined unsafe by an appropriate health or regulatory agency.

Microfiltration: The separation or removal from a liquid of particulates and microorganisms in the size range of 0.1 to 2 microns in diameter.

Microgram: One-millionth of a gram
(3.5 X 10^-8 oz = 0.000000035 oz.).

Micrograms Per Liter: One microgram of a substance dissolved in each liter of water. This unit is equal to parts per billion (ppb) since one liter of water is equal in weight to one billion micrograms.

Microhm: One millionth of an ohm. The unit of measurement for testing the electrical resistance of water to determine its purity. The closer water comes to absolute purity, the greater its resistance to conducting an electric current. Absolutely pure water has a specific resistance over 18 million ohms across one centimeter at a temperature of 78 degrees F (25 degrees C).

Micron: A metric unit of length equal to one millionth of a meter or one thousandth of a millimeter or about 0.00003937 inches. Also called a micrometer, µm.

Micron Rating: A measurement applied to filters or filter media to indicate the particle size at which suspended solids above that size will be removed. As used in the water treatment industry standards, this may be an absolute rating or a nominal rating.

Microorganism: A living organism invisible or barely visible to the naked eye and generally observable only through a microscope. Also called a microbe. Microorganisms are generally considered to include algae, bacteria, fungi, protozoa, and viruses. Microorganisms are generally considered to include algae, bacteria, fungi, protozoa, and viruses.

Microporous Resin: Ion exchange resin with low porosity, usually polystyrene cross-linked typically with about three percent divinylbenzene. The lower cross-linking means microporous resins also have less strength and less resistance to degradation, swelling, and mushing.

Microsiemens: One-millionth of a siemens (formerly called mho). The microsiemens is the practical unit of measurement for conductivity and is used to approximate the total dissolved solids content of water. Water with 100 mg/L (ppm) of sodium chloride will have a specific resistance of 4,716 ohms-centimeter and a conductance of 212 microsiemens per centimeter. Absolute pure water, from a mineral content standpoint, has a conductivity of 0.03 microsiemens per centimeter at 25 degrees C (78 degrees F). Also called micromhos.

Microwatt: One millionth of a watt.

Microwatt-Seconds Per Square Centimeter: A unit of measurement of intensity and retention or contact time in the operation of ultraviolet systems. Abbreviated as μWs/cm².

Midpoint: The point at or near the middle of a scale or set of experimental results data in scientific analyses.

Midpoint Distributor: The lateral (horizontal) distribution system located at the interface where stratified anion and cation beds in a mixed bed ion exchange deionizer meet.

Milligram (mg): One-thousandth of a gram (3.5 X 10^-5 oz = 0.000035 oz).

Milligrams per Liter (mg/L): A measure of concentration of a dissolved substance. A concentration of one mg/L means that one milligram of a substance is dissolved in each liter of water. For practical purposes, this unit is equal to parts per million (ppm) since one liter of water is equal in weight to one million milligrams. Thus, a liter of water containing 10 milligrams of calcium has 10 parts of calcium per one million parts of water, or 10 parts per million (10 ppm).

Milliliter (mL): A unit of volume measure equal to 1/1000 liter (or one cubic centimeter); the volume occupied by one gram of pure water at 4 degrees C at 760 mm of pressure or standard atmospheric pressure.

Millimeter (mm): A unit of length equal to 0.001 of an inch. The diameter of wires and tubing is measured in millimeters, as is thickness of plastic sheeting.

Millimicron: A unit of length equal to 10^-3 microns (one thousandth of a micron), 10^-6 millimeters, or 10^-9 meters; correctly called a nanometer (nm).

Million-gallons per day (MGD): A measure of water flow.

Mineral (1): An inorganic (nonliving, non-carbon containing) substance which occurs naturally in the earth and has a composition that can be expressed as a chemical formula and a set of characteristics (crystalline structure, hardness, etc.) common to all minerals. Examples of minerals are sulfur, salt, and stone. Certain organic substances, such as coal, are also sometimes referred to as minerals. The word mineral is also used to refer to matter derived from minerals, such as inorganic ions found in water and reported as mineral content.

Mineral (2): Term used in the water treatment industry to refer to naturally-occurring inorganic cation exchangers formerly used in water softeners – as opposed to the synthetic organic resins used today for water softening.

Mineral Acidity: Acidity in water due to the presence of strong inorganic acids such as hydrochloric, nitric, and sulfuric acids as opposed to weak acidity due to such acids as carbonic acid or acetic acid. Mineral acidity is usually expressed in water analysis as FMA (free mineral acidity).

Mineral Salt: A chemical compound formed by the combination of a mineral acid and a base. Minerals from dissolved rock exist in water in the form of dissolved mineral salts. An excess of mineral salts can give water a disagreeable taste or even be harmful to human health.

Mineral Water: Water which is naturally or artificially impregnated with mineral salts or gases (carbon dioxide). The term is also used to designate bottled water that contains no less than 250 ppm total dissolved solids (TDS) and originates from a protected groundwater source.

Mineral-Free Water: Water produced by either distillation or deionization. This term is sometimes found on labels of bottled water as a substitute term for distilled or deionized water.

Mineralization: The microbial conversion of an element from an organic to an inorganic state.

Miners Salt: Another name for mined rock salt.

Miscible: Able to be mixed together or dissolved into each other to produce a homogenous substance.

Mixed Bed: The intermix of two or more filter or ion exchange products in the same vessel during a service run. The most common use is in ion exchange systems having a 40/60 percent cation to anion resin bed such as that for a deionization polisher unit. In filtration, there may be an intermix of two or more media in a single tank with each stratified into separate layers.

Mixed Liquor: A mixture of activated sludge and waters containing organic matter undergoing activated sludge treatment in the aeration tank of a waste water treatment system.

Mixed Media: The use of two or more media products in a single filtration loose media bed where the products are intermixed–rather than in stratified layers. For example, the intermix use of calcite and magnesia in pH modification.

Mode: In statistics, the most frequently occurring number in a set of numbers. For example, in the set 1,2,4,4,4,4,6,8,10, the number 4 is the mode.

Modeling: Use of mathematical equations to simulate and predict real events and processes.

Module: The membrane element and its housing in a reverse osmosis unit.

Molar of Molarity: A molar solution consists of one-gram molecular weight of a compound dissolved in enough water to make one liter of solution. A gram molecular weight is the molecular weight of a compound in grams. For example, the molecular weight of sulfuric acid (H₂SO₄) is 98. A one M solution of sulfuric acid would consist of 98 grams of H₂SO₄ dissolved in enough distilled water to make one liter of solution.

Mole: Abbreviated as “mol”. A measure used in chemistry to describe the number and mass of constituent particles relative to the mass and number of particles in 12.00 grams of elemental carbon. Just as the term “dozen” indicates 12 items, the term “mole” indicates 6.022140857 x 10²³ molecules. SEE ALSO Avogadro’s number.

Molecular Weight (MW): The molecular weight of a compound in grams is the sum of the atomic weights of the elements in the compound. For example, the molecular weight of sulfuric acid (H₂SO₄) in grams is 98.

Molecule: The smallest particle of an element or compound that retains all of the characteristics of the element or compound. A molecule is made up of one or more atoms. The helium molecule, for example, has only one atom per molecule. Oxygen molecules (O₂) have two atoms; ozone molecules (O₃) have three atoms. Molecules found in chemical compounds often have many atoms of various kinds.

Monel: Trade name for a series of corrosion resistant alloys made of nickel and copper.

Monitoring: Measuring concentrations of substances in environmental media or in human or other biological tissues.

Monitoring Light Sensor: An indicator light, electrically or electronically activated, which is positioned in the effluent (product water) stream of a piece of water treatment equipment (deionizer, distiller, reverse osmosis unit, or electrodialysis unit) to detect and signal changes in the water quality which might indicate malfunction of the equipment. Some lights remain on while water quality is within the desired range and go out if the quality of the water falls into the unacceptable range. Other sensors use red and green light signals.

Monitoring Wells: Wells used to collect groundwater samples for analysis to determine the amount, type, and spread of contaminants in groundwater.

MonoBed: A product trade name for a fully regenerated ion exchange mixed bed (strong acid cation H⁺ and strong base anion OH^–).

Monochromatic: Consisting of radiation or rays, such as ultraviolet rays, of a single wave length or of a very small range of wave lengths.

Monomer: A molecule of low molecular weight capable of reacting with identical or different monomers to form polymers.

Monomictic: Lakes and reservoirs which are relatively deep, do not freeze over during the winter months, and undergo a single stratification and mixing cycle during the year. These lakes and reservoirs usually become destratified during the mixing cycle, usually in the fall of the year.

Monovalent: Having a valence of one, such as the cuprous (copper) ion, Cu⁺. Also called univalent.

Mortality: Death.

Most Probable Number (MPN): Term indicating the number of organisms in a sampled water which, according to statistical theory, would most likely produce the results observed in the multiple tube fermentation bacteriological tests. Usually expressed as a number per 100 ml of water.

Mother Liquor: 1. Residual brines, containing chiefly calcium and magnesium chlorides, obtained after the salt has been crystallized and removed from solution. The term “mother liquor” is widely used when salt is produced by use of vacuum pan and gainer operations. In the solar salt evaporation process, the term “bitterns” is often used in place of the term “mother liquor”.
2. A solution substantially freed from undissolved matter by a solid/liquid separation process, such as filtration or decanting.

Motile: Capable of self-propelled movement. A term that is sometimes used to distinguish between certain types of organisms found in water.

Motive Flow: The water flow rate (e.g., gallons per minute) through a venturi injector that provides the suction at the injection port of the injector to induce the flow of another liquid (such as a regenerant) or gas (such as air or ozone) into the flow of water.

Motor Efficiency: The ratio of energy delivered by a motor to the energy supplied to it during a fixed period or cycle. Motor efficiency ratings will vary depending upon motor manufacturer and usually will range from 88.9 to 90.0 percent.

Mudballs: Material that is approximately round in shape and varies from pea-sized up to two or more inches in diameter. This material forms in filters and gradually increases in size when not removed by the backwashing process.

Mulch: Any substance spread or allowed to remain on the soil surface to conserve soil moisture and shield soil particles from the erosive forces of raindrops and runoff.

Multifunctional Medium: A single filter or ion exchange medium used to treat water for the removal of more than one constituent. Examples are activated carbon for chlorine removal and sediment filtration, calcite for pH modification and filtering of precipitated iron, or cation resin for reduction of dissolved iron as well as hardness removal.

Multilayered Bed: A media bed in which more than one filter or ion exchange medium is used in the same vessel, with each medium retaining its stratified position as a layer – even after specified backwashing is performed – due to differences in media densities.

Multiple Use: Use of land for more than one purpose; i.e., grazing of livestock, wildlife production, recreation, watershed, and timber production. Could also apply to use of bodies of water for recreational purposes, fishing, and water supply.

Multiport Valve: A master control valve used in a filter, deionizer, or water softener to control all the necessary steps in the regeneration process or the backwashing and rinse down of filters. Term originated by the Permutit Company of New York.

Multistage Model: Mathematical model based on the multistage theory of the carcinogenic process, which yields risk estimates either equal to or less than the one-hit model.

Multistage Pump: A pump that has more than one impeller. A single-stage pump has one impeller.

Municipal Sewage: Wastes (mostly liquid) originating from a community; may be composed of domestic waste waters and/or industrial waste waters.

Municipal Softening: A hardness reduction process performed at municipal central treatment plants to deliver water in the range of 5 to 12 grains per gallon total hardness.

Municipal Water: Water that has been processed at a central plant to make it potable or “safe to drink” and which is then distributed to homes and businesses via water mains. Either public agencies or private companies can be involved in providing “municipal water”. The term is a general one used to refer to the common source of water in most urban and suburban areas–as opposed to water obtained from separate proprietary sources such as private wells.

Mushing: Mushing of water softener salt occurs when salt pellets break down into their crystallized form. If a water softener brine tank is caked with salt or if a ridge of salt appears in the unit, the salt has either mushed or bridged, or both. Both salt mushing and salt bridging conditions prevent proper circulation of salt in the unit and require that the brine system be cleaned.

Mutagen: An agent that causes a permanent genetic change in a cell other than that which occurs during a normal genetic recombination.

Mutagenicity: The capacity of a chemical or physical agent to cause permanent alteration of the genetic material within living cell.

megohm: A unit of electrical resistance equal to one million ohms.

mg/L: Milligrams per liter.

NAICS: SEE North American Industry Classification System.

NOAEL – No observed adverse effect level: The highest dose in a toxicity experiment which did not produce an observable adverse effect.

NOEL: No-observed-effect level; dose level at which no effects are noted.

NPL (National Priorities List): A list of Superfund sites chosen for immediate attention.

NSDWR: National Secondary Drinking Water Regulations.

NTNCWS: See nontransient noncommunity water system.

NTP: National Toxicology Program

NTU: Nephelometric turbidity unit.

Nanofiltration: A membrane treatment process which falls between reverse osmosis and ultrafiltration on the filtration/separation spectrum. The nanofiltration process can pass more water at lower pressure operations than reverse osmosis, can remove particles in the 300 to 1,000 molecular weight range such as humic acid and organic color bodies present in water, and can reject selected (typically polyvalent) salts. Nanofiltration may be used for selective removal of hardness ions in a process known as membrane softening.

Nanometer (nm): One billionth (10^-9) of a meter, and equal to one millimicron or 10 angstroms.

National Pollutant Discharge Elimination System (NPDES): The NPDES permit is the regulatory agency document issued by either a federal or state agency which is designed to control all discharges of pollutants from point sources in U.S. waterways. NPDES permits regulate discharges into navigable waters from all point sources of pollution, including industries, municipal treatment plants, large agricultural feed lots, and return irrigation flows.

Natural Softening: Naturally softened water comes to us in many ways: rain, snow, sleet, hail, fog, mist, dew and melting glaciers. This is a result of the normal hydrologic cycle of evaporation and condensation that separates mineralized water from its salts.

Natural Sparkling Water: Carbonated water whose carbon dioxide content is from the same source as the water itself.

Naturally Soft Water: A term that classifies naturally occurring low hardness water such as a surface water or rain water as “soft” even though the hardness content is usually greater than 1 gpg but often less than 3 gpg. Naturally soft waters generally have a high carbon dioxide content with an acidic pH and are prone to cause corrosion. This characteristic is not true for “softened” water which has been treated to reduce the hardness content using ion exchange.

Near the first service connection: Pertaining to public water system monitoring at one of the 20 percent of all service connections in the entire system that are nearest the water supply treatment facility, as measured by water transportation time within the distribution system.

Necrosis: Death of cells or tissue.

Negative Charge: The electrical potential of an atom which gains one or more electrons, therefore leaving it with more electrons than protons. Anions carry negative charges.

Negative Head: A condition of negative pressure or of partial vacuum.

Negative Pressure: A pressure below that of the existing atmospheric pressure taken as a zero reference.

Nematode: Members of the phylum Nematoda, commonly called roundworms. Nematodes have tiny cylindrical thread-like bodies that are pointed at both ends and covered with tough cuticle or skin-like membranes. Many are free-living dwellers in soil and water; others, like hookworms, Ascaris, pinworms, trichina worms, and filaria worms are parasites of man, animals, and plants.

Neoplasm: An abnormal growth or tissue, as a tumor.

Nephelometer: An instrument for measuring turbidity in water using a photometric analytical technique for measuring the light scattered by finely divided turbidity or colloidally dispersed particles suspended in water.

Nephelometric: A means of measuring turbidity in a sample by using an instrument called a nephelometer. A nephelometer passes light through a sample, and the amount of light deflected (usually at a 90-degree angle) is than measured.

Nephelometric Turbidity Unit (NTU): The standard unit of measurement used in the water analysis process to measure turbidity in a water sample. The NTU has replaced the formerly used Jackson turbidity unit (JTU).

Neurotoxicity: Exerting a destructive or poisonous effect on nerve tissue.

Neutral: In water chemistry, the midpoint (neutral) reading of 7.0 on the pH scale, indicating that the solution (water) producing the neutral reading will produce neither an acid nor alkaline reaction. A 7.0 reading on the pH scale means that there are an equal number of free hydrogen (acidic) ions and hydroxide (basic) ions. As relates to electricity, a condition of being uncharged because of a balance between negative and positive charges. The condition of neutrality means that there is neither an excess nor a lack of electrons.

Neutralite: A trade name for a calcite mineral product (crushed southern limestone) which is used in loose media bed filters to modify the pH of low pH water sources.

Neutralization: The addition of either an acid to a base or a base to an acid to produce a more nearly neutral solution. The use of alkaline or basic materials to neutralize acidity of some water is common practice in water processing. Neutralization does not always mean the attaining of pH 7.0. When a strong acid reacts (is neutralized) with a weak base, the resulting pH may remain less than 7.0; when a strong base reacts with a weak acid, the pH may remain greater than 7.0.

Neutralizer: 1. An alkaline substance such as calcium carbonate (calcite) or magnesium oxide (magnesia) used to neutralize acidic waters or an acidic substance such as acetic acid or dilute hydrochloric acid used to neutralize alkaline waters.
2. The term “neutralizer” is commonly used to refer to calcite or magnesia acid-neutralizing filters used to neutralize acidity and/or reduce free carbon dioxide in water and thereby raise the pH of acidic water.

Neutron: A fundamental particle found in the nucleus of an atom. A neutron has a mass equal to that of a proton but carries no charge.

Newton: The force necessary to give acceleration of one meter per second to one kilogram of mass.

Nitrate: A natural nitrogen compound (NO₃^–) sometimes found in well or surface waters. In high concentrations, nitrates can be harmful to young infants or young livestock.

Nitrification: The biochemical transformation of ammonium nitrogen to nitrate nitrogen.

Nitrification Inhibitor: A chemical that slows down the conversion of ammonium to nitrate nitrogen.

Nitrogen Fixation: The biological or chemical process by which elemental nitrogen, from the air, is converted to organic or available nitrogen.

Nitrogenous: A term used to describe chemical compounds (usually organic) containing nitrogen in combined forms. Proteins and nitrates are nitrogenous compounds.

No-salt Water Conditioner: SEE saltless water treatment device

No-salt Water Softener: SEE saltless water treatment device; water softener

Noble: Chemically unreactive, especially toward oxygen or resists chemical action such as corrosion caused by air, water, or (to a lesser degree) acids. Gold, silver, platinum, palladium, and mercury are said to be “noble metals” because they don’t rust and are resistant to acid damage. Certain gases are called “noble gases” because they are inert (chemically inactive and stable.)

Noble Metal: Chemically inactive metal (such as gold). A metal that does not corrode easily and is much scarcer (and more valuable) than the so-called useful or base metals.

Nominal Diameter: An approximate measurement of the diameter of a pipe. Although the nominal diameter is used to describe the size or diameter of a pipe, it is usually not the exact inside diameter of the pipe.

Nominal Filter Rating: Filter rating indicating the approximate size particle, the majority of which will not pass through the filter. It is generally interpreted as meaning that 85 percent of the particles of the size equal to the nominal filter rating will be retained by the filter.

Noncarbonate Hardness (permanent hardness): The hardness content in water associated with strong acid anions of chloride, sulfate, and/or nitrate. Noncarbonate hardness does not form hard scale upon heating.

Noncommunity Water System (NCWS): A public water system that is not a community water system. There are two types of NCWSs: transient and nontransient.

Nonconventional Pollutant: Any pollutant which is not statutorily listed or which is poorly understood by the scientific community.

Nondegradable: Resistant to decomposition or decay by biological means such as bacterial action or from chemical or physical causes such as oxidation, heat, sunlight, or solvents.

Nonhardening Salt: Salt containing amounts of agents such as calcium or magnesium chloride which become soft or liquid by attracting and absorbing moisture from the air and preventing salt caking and bridging.

Nonionic Polymer: A polymer that has no net electrical charge.

Nonpathogenic: Not disease-producing.

Nonpoint Source: Pollution sources which are diffuse and do not have a single point of origin or are not introduced into a receiving stream from a specific outlet. The pollutants are generally carried off the land by stormwater runoff. the commonly used categories for non-point sources are; agriculture, forestry, urban, mining, construction, dams and channels, land disposal, and saltwater intrusion.

Nonpotable: Water that may contain objectionable pollution, contamination, minerals, or infective agents and is considered unsafe and/or unpalatable for drinking.

Nonsettleable Solids: Very small, fine suspended solids, typically colloidal particles of less than 0.1 microns in diameter, which will not settle out of calm nonturbulent water, sewage, or other liquids in what is considered a reasonable time of about two hours.

Nontransient Noncommunity Water System (NTNCWS): A public water system that regularly serves at least 25 of the same nonresident persons per day for more than six months per year.

Normal Flow Filtration: The flow of the entire feedwater stream in one direction directly through the filter media. The flow is usually “normal” or perpendicular to the media surface area.

Normal Solution: A normal solution contains one-gram equivalent weight of dissolved substance in a liter of solution. The equivalent weight of an acid is that weight which contains one-gram atom of ionizable hydrogen or its chemical equivalent. For example, the equivalent weight of sulfuric acid (H₂SO₄) is 49 (98 divided by 2 because there are two replaceable hydrogen ions). A one N solution of sulfuric acid would consist of 49 grams of H₂SO₄ dissolved in enough water to make one liter of solution.

North American Industry Classification System (NAICS): The standard statistical classification system, adopted in 1997 by the United States Office of Management and Budget (OMB), that assigns an industry number to businesses and business units by type of economic activity. The NAICS has been harmonized with and also adopted by Mexico and Canada. It replaces the Standard Industrial Classification (SIC) system used in the U.S. from 1938 and until 1997. The NAICS is a standard industry classification system that facilities the collection, tabulation, presentation, and analysis of data relating to establishments and ensures that data about the U.S. economy published by U.S. statistical agencies are uniform and comparable among the North American countries. The NAICS uses a six-digit numerical coding system to identify particular industries and their placement in the hierarchical structure of the classification system. The first two digits group establishments (or locations at which an economic activity occurs) into one of 20 sectors, such as for example, Agriculture, Mining, Construction, Manufacturing, Wholesale Trade, Retail Trade, and Administration and Support Services. The remaining digits designate one of the 1,170 industries identified in NAICS. When any employer applies for an Employer Identification Number (EIN), information about the type of activity in which that business is engaged is requested in order to assign a NAICS code. In addition, statistical agencies such as the Census Bureau and the Bureau of Labor Statistics assign NAICS codes based on information reported to them. Water treatment equipment manufacturing, for example, is in NAICS 333319, water softener and water conditioning direct selling and service providers are in NAICS 454390, water softening and conditioning equipment wholesaling is in 421720, water softening and conditioning compounds and materials wholesaling is in 422690, and water softening and conditioning support services are in 561990. Bottled water manufacturing (purifying and bottling) is in NAICS 312112, bottled water stores are in NAICS 445299, bottled water wholesaling is in NAICS 422490, and other water treatment and distribution is in NAICS 221310.

Nosocomial: Acquired after admittance to a hospital.

Not Detectable: A term used in reporting test results to mean that the substance being tested cannot be detected by the equipment or method being used for this particular test. This term implies that it is possible that trace amounts may be present in quantities too small to be detected by the test equipment or method.

Nucleus: A term used in reporting test results to mean that the substance being tested cannot be detected by the equipment or method being used for this particular test. This term implies that it is possible that trace amounts may be present in quantities too small to be detected by the test equipment or method.

Nutrient: Any substance that is assimilated (taken in) on organisms and promotes growth. For example, carbon dioxide, nitrogen, phosphorous, potassium, and numerous mineral elements are essential nutrients which promote the growth of plants. Water and oxygen are also included in this definition.

Nutrient Pollution: Contamination of water resources by excessive inputs of nutrients: in surface waters, excess algae production is a major concern.

ORP (Oxidation-Reduction Potential): The electrical potential required to transfer electrons from one compound or element (the oxidant) to another compound or element (the reductant): used as a qualitative measure of the state of oxidation in water treatment systems.

OSHA: The Williams-Steiger Occupational Safety and Health Act of 1970 (OSHA) is a law designed to protect the health and safety of industrial workers and also the operators of water supply systems and treatment plants. OSHA also refers to the federal and state agencies which administrator the OSHA regulations.

Occlusion: An absorption process by which one substance is taken in and retained in the interior rather than on the external surface of another, sometimes occurring by coprecipitation.

Odor Threshold: The minimum odor of a water sample that can just be detected after successive dilutions with odorless water. Also called threshold odor.

Off-Gas: Air or vapor given off or expelled as a byproduct or result of an operation or treatment process.

Offset (or Droop): The difference between the actual value and the desired value (or set point); characteristic of proportional controllers that do not incorporate reset action.

Offstream Uses: Water withdrawn from surface or groundwater sources for use at another place.

Ohm: The standard unit for measuring resistance to the passage of an electrical current. One ohm is equal to the resistance created between two points on a conductor when a potential difference of one volt creates a current of one ampere. An ohm is also equal to the resistance offered by a column of mercury which is 1.0²mm in cross sectional area and 106.3 cm long at 0 degrees C. Electrical resistance in a solution is often related to the electrolyte concentration in the solution.

Oil of Vitriol: An old and now obsolete term once used for sulfuric acid (H,₂SO₄).

Oleophilic: Having a strong affinity (liking) for oil, and thereby exhibiting the characteristic of adsorbing oily-type substances. Activated carbon is an oleophilic material. The opposite of oleophobic.

Oleophobic: Having a strong aversion (dislike) for oil, and thereby exhibiting the characteristic of repelling oily-type substances. Water is oleophobic. The opposite of oleophilic.

Oleum: (H₂SO₄ + SO₃) The Latin word for oil. Oleum is a solution of sulfuric acid and sulfur trioxide that is a form of fuming sulfuric acid. The term is used to describe a stage in the production of sulfuric acid.

Olfactory Fatigue: A condition in which a person’s nose, after exposure to certain odors, is no longer able to detect the odor.

Oligo-dynamic Action: The bacteriostatic action exerted by very small amounts of heavy metals such as copper, silver, and zinc which deactivates bacteria and creates a hostile environment for the growth of bacterial colonies.

Oligotrophic: Reservoirs and lakes which are nutrient poor and contain little aquatic plant or animal life.

Oncology: Study of cancer.

One-Hit Model: Mathematical model based on the biological theory that a single “hit” of some minimum critical amount of a carcinogen at a cellular target namely, DNA can initiate an irreversible series of events, eventually leading to a tumor.

Oocyst: The fertilized egg form of parasitic sporozoa protozoa such as Giardia, Cryptosporidium, and Cyclospora that is encapsulated in a tough shell. The oocyst is an environmentally resistant transmissible form of certain protozoan parasites that is excreted in the feces of an infected host and carried viably in unfiltered water supplies.

Opacity: The capacity of matter to block the passage of light or other radiant energy such as heat. A measure of opacity might be the percentage of light transmission through a plume. Opacity is the opposite of transparency, and an object with a high degree of opacity is said to be opaque.

Operating Cycle: In filtration applications, the complete filtration process consisting of filter service, backwash and rinse, and return to service. As relates to ion exchange, the cycle of service run, backwash and regeneration, slow rinse, fast rinse, and return to service.

Operating Pressure: The manufacturer’s specified range of pressure expressed in pounds per square inch (psi) within which a water processing device or water system is designed to function. A range of 30 to 100 psi is often indicated. Also called working pressure.

Operating Temperature: The manufacturer’s recommended feedwater or inlet water temperature for a water treatment system.

Operation and Maintenance Costs: The ongoing, repetitive costs of operating a water system; for example, employee wages and costs for treatment chemicals and periodic equipment repairs.

Optimal Corrosion Control Treatment: The corrosion control treatment by a public water system that minimizes the lead and copper concentrations at users’ taps while ensuring that the treatment does not cause the water system to violate any national primary drinking water regulations.

Oral: Of the mouth; through or by the mouth.

Organic: 1. Having the characteristics of, or being derived from, a living organism, plant, or animal.
2. Containing carbon (although a few very simple carbon compounds such as the carbon oxides, the carbides, carbon disulfide, and metallic carbonyls and carbonates are considered inorganic). Over 6,000,000 carbon-containing organic compounds have been identified and named.

Organic Chemical: A chemical having a carbon-hydrogen structure.

Organic Iron: Iron that is bound or complexed with organic compounds, such as naturally occurring humic and fulvic acids. In waters laden with a high level of these vegetation decay products, iron is sometimes present in an organic form. The decaying process of vegetation produces humic and fulvic acids. Iron will react with these natural complexation or chelating agents to form either an insoluble colloid with humic acid and humin, or a soluble complex chelate with fulvic acid and tannin. Organic iron can be present in a colorless form, but most often occurs as a yellow, yellowish- brown, or pink color. The humic acid and humin colloids developing the color seem to be permanently suspended in the water due to their particle size, normally less than 0.1 micron. Organic iron can also be referred to as tannin, heme iron, complexed iron, or pink iron.

Organic Matter: Substances consisting of, or derived from, plant or animal matter as opposed to inorganic matter which is derived from rocks, ores, and minerals. Organic matter is characterized by its carbon-hydrogen structure.

Organics: Term often used to describe any (or all) of the compounds, natural or man-made, with chemical structures based upon carbon. Examples are hydrocarbons, wood, sugars, proteins, methane, plastics, petroleum-based compounds, solvents, pesticides, herbicides, trihalomethane (THM), and trichlorethylene (TCE).

Organism: Any form of animal or plant life.

Organoleptic: Affecting perceptions that are stimulated by senses in the eye, ear, skin, nose, or mouth. Used to describe subjective characteristics such as flavor, odor, color, appearance, and related factors of food and water.

Orifice: 1. An opening, such as a hole or vent in something
2. In water treatment, usually an opening through which water can pass or a restricted opening placed in a pipe line to provide a means of controlling or measuring flow. For example, a flow controller.

Ortho: 1. A prefix used in inorganic chemistry to mean the most hydrated form of an acid or its salt, in contrast to a less hydrated form which is indicated by the meta- prefix. For example, H₃PO₄ is orthophosphoric acid; HPO₃ is metaphosphoric acid.
2. In organic chemistry, ortho, meta, and para are terms related to the position of atoms or radicals in the benzene ring of aromatic organic compounds.

Orthophosphate: 1. A salt that contains phosphorus as PO₄^3-.
2. A product of the hydrolysis of condensed (polymeric) phosphates, i.e., the most hydrated or reverted (“broken down”) and stable form of phosphate compounds. Orthophosphates cannot sequester metal ions and hardness, but they can form passivating films on anodic sites to suppress electrochemical corrosion reactions in metallic plumbing.
3. A nutrient required for plant and animal growth.

Orthotolidine: Orthotolidine is a colorimetric indicator of chlorine residual. If chlorine is present, a yellow-colored compound is produced. This reagent is no longer approved for chemical analysis.

Osmosis: The natural tendency for water to spontaneously pass through a semipermeable membrane separating two solutions of different concentrations (strengths). The water will naturally pass from the weaker (less concentrated) solution containing fewer particles of dissolved substance to the stronger (more concentrated) solution containing more particles of a dissolved substance. Thus, natural osmosis causes the stronger solution to become more diluted and tends to equalize the strength of the solutions on both sides of the membrane.

Osmotic Pressure: The pressure and potential energy difference which exists between two solutions on either side of a semipermeable membrane because of the tendency of water to flow in osmosis. Every 100 ppm (mg/L) of TDS generates about one pound per square inch of osmotic pressure. This osmotic pressure must first be overcome by water pressure for a reverse osmosis membrane to become effective.

Osmotic Stability: An expression of the ability of an ion exchange resin to resist physical degradation due to volume changes (shrinkage and swelling) imposed by repeated applications of dilute and concentrated solutions.

Overall Pump Efficiency: The combined efficiency of a pump and motor together. Also called the wire-to-water efficiency.

Overdraft: The pumping of water from a groundwater basin or aquifer in excess of the supply flowing into the basin. This pumping results in a depletion or “mining” of the groundwater in the basin.

Overflow Rate: One of the guidelines for the design of settling tanks and clarifiers in treatment plants. Used by operators to determine if tanks and clarifiers are hydraulically (flow) over- or underloaded. Also called surface loading. Overflow Rate (GPD/sq.ft) = Flow (GPD)/Surface Area (sq.ft)

Overrun: Operating a filter or ion exchange system beyond its predetermined exhaustion point. This means the filter or system is unlikely to be as effective as it should be, and it probably needs some regeneration to restore capacity (ion exchange), or a cleansing, backwashing, or media/element replacement to reduce headloss and restore capacity (mechanical, adsorption, or neutralization filter).

Overturn: The almost spontaneous mixing of all layers of water in a reservoir or lake when the water temperature becomes similar from top to bottom. This may occur in the fall/winter when the surface waters cools to the same temperature as the bottom waters and also in the spring when the surface waters warm after the ice melts. Also called turnover.

Oxidation: The process in which a molecule, atom, or ion loses electrons to an oxidant. The oxidized substance (which lost the electrons) increases in positive valence. Oxidation never occurs alone, but always occurs as part of the oxidation-reduction (redox) reaction. The reduced substance gains electrons and thereby decreases in positive valence.

Oxidation (electrodialysis): A chemical reaction which occurs at the anode and results in the loss of electrons from the anodic material.

Oxidation (electrodialysis): A chemical reaction which occurs at the anode and results in the loss of electrons from the anodic material.

Oxidation (ion exchange): Specific attack on the cross linking of the co-polymer of ion exchange resins by an oxidant (chlorine, peroxide, ozone, or others) leading to degradation (loss of structure of resin beads) and shortening of the resin life.

Oxidation Pond (waste water treatment): In wastewater treatment, a man-made lake or body of water within which wastes are consumed by bacteria, and where this biological oxidation process is enhanced by the transfer of oxygen to the water from the air. Oxidation ponds are most frequently used together with other waste treatment processes.

Oxidation-Reduction (Redox) Reaction: The combination of the processes involved in the flow of electrons from a reducing agent (reducer) to an oxidizing agent (oxidant). The total number of electrons lost by one substance is the same as the total number of electrons gained by another substance. Oxidation and reduction always occur together simultaneously and are really opposite sides of the same reaction, often called the redox reaction. In earlier years, oxidation referred to the combining of a substance with, or addition of, oxygen, and reduction meant the loss or reduction of oxygen. However, as chemistry became more advanced, it was seen that the real key to what was happening was the loss or gain of electrons. Now, the definitions accepted are as follows: Oxidation is the loss of electrons from the reducing agent (which is said to have “been oxidized” in the process). Since electrons carry negative charges, oxidation results in an increase of positive valence. Reduction is the acquiring of electrons (the ones lost in the oxidation process) by the oxidizing agent (which is said to have “been reduced” in the process). Because electrons (carrying negative charges) have been acquired, reduction results in a lowering (a reduction) of positive valence. It may be helpful to remember that the word “agent” refers to an active substance that produces or brings about some effect. Therefore, the oxidizing agent is the substance that brings about oxidation; the reducing agent is the substance that brings about reduction.

Oxidation-Reduction Potential (ORP): The electrical potential required to transfer electrons from one compound or element (the oxidant) to another compound or element (the reductant); used as a qualitative measure of the state of oxidation in water treatment systems.

Oxidize: To increase a molecule or ion in positive valence; to lose electrons to an oxidizing agent.

Oxidizing Agent: A chemical substance that gains electrons (i.e., is reduced) and brings about the oxidation of other substances in chemical oxidation and reduction (redox) reactions. Examples of oxidizing agents include oxygen, ozone, chlorine, peroxide.

Oxidizing Filter: A type of filter used to change the valence state of dissolved molecules, making them insoluble and, therefore, filterable. For example, a filter that oxidizes ferrous iron, manganous manganese, and/or anionic sulfur by use of catalytic media such as manganic oxides and then filters the oxidized precipitates out of the water.

Oxygenate: To impregnate or combine with oxygen such as the forced draft step in aeration. Maximum oxygen exposure.

Ozonation: The process of feeding ozone into a water supply for the purpose of decolorization, deodorization, disinfection, or oxidation.

Ozone Destruction: The step by which a component unit of an ozonation system destroys all or some of the ozone present in the off-gas being vented.

Ozone Enrichment: A step in the ozonation process in which more ozone is added to a gas which previously contained ozone.

Ozone Half-Life: The period of time required for 50 percent of a given quantity of ozone to decompose at a specific temperature and pressure.

Ozone-(O3): A very strong oxidizing agent which is unstable and must be generated on site. Ozone is a highly reactive form of oxygen and can be produced by sending a high voltage electrical discharge through air or oxygen (such as occurs in a lightning storm). Some degree of ozone can also be produced by certain types of ultraviolet lamps. Ozone is an excellent oxidizing agent and bactericide.

Ozonide: A compound which occurs as a byproduct of ozonation.

Ozonolysis: 1. The oxidation of an organic material by ozone.
2. The use of ozone as a tool in analytical chemistry to locate double bonds in organic compounds.

Ozonosphere: A region in the upper atmosphere containing a relatively high concentration of ozone which absorbs certain wavelengths of solar ultraviolet radiation that are not screened out by other substances in the atmosphere.

PEX: cross-linked polyethylene.

POE: Point of entry.

POU: Point-of-use.

PSA: Pressure swing adsorption.

PVC: Polyvinyl chloride.

Pa: Pascal.

Packed Bed: A bed of filter or ion exchange medium which is completely retained so that no bed expansion can occur, and no backwash step is used to reclassify the filter or resin. Packed beds are usually part of the design features in ion exchange water softeners used to obtain high capacity and increased regeneration efficiency.

Packed Tower Aeration: A method of treating water to remove volatile organic chemical (VOCs) contaminants. As water is mixed with air, VOCs move from water to air which then passes through carbon filters to trap the contaminants.

Palatable: Water at a desirable temperature that is free from objectionable tastes, odors, colors, and turbidity. Pleasing to the senses.

Parshall Flume: A device used to measure the flow in an open channel. The flume narrows to a throat of fixed dimensions and then expands again. The rate of flow can be calculated by measuring the difference in head (pressure) before and at the throat of the flume.

Particle: A very tiny, separate subdivision of matter.

Particle Count: The results of a microscopic examination of treated water with a special “particle counter” which classifies suspended particles by number and size.

Particle Filtration: Filtration of particles in the size range of two microns or larger in diameter. Particle filtration is typically handled by cartridge filters and media filters.

Particle Size: As used in water industry standards, this term refers to the size, expressed in microns, of a particle suspended in water as determined by the smallest dimension.

Particulate: A very small solid suspended in water which can vary widely in size, shape, density, and electrical charge. Colloidal and dispersed particulates are artificially gathered together by the processes of coagulation and flocculation.

Partition Coefficient: A measure of the extent to which a pesticide is divided between the soil and water phases.

Parts Per Billion (ppb): A measure of proportion by weight which is equivalent to one-unit weight of solute (dissolved substance) per billion unit weights of the solution. This measurement is often used as a measure of concentration when analyzing water for contaminants. Since one liter of water weighs one billion micrograms, one ppb is the equivalent of one microgram per liter when used in water analysis.

Parts Per Million (ppm): A measure of proportion by weight which is equivalent to one unit of weight of solute (dissolved substance) per million weights of solution. Since one liter of water weighs one million milligrams, one ppm is equal to one milligram per liter (mg/L). Milligram per liter is the preferred unit of measure in water or waste water analysis.

Pascal (Pa): A unit of pressure equal to one newton of force per square meter. One thousand pascals equal one kilopascal (KPa); a kilopascal equals 0.145 pounds per square inch. 1 psi = 6895 Pa = 6.895 kN/sq.m = 0.0703 kg/sq.cm

Pasteurization: A process for the partial sterilization (disinfection) of a substance, usually a liquid, by heating it to a critical temperature for a specified period of time. Pasteurization does not greatly change the chemical composition of the sterilized substance.

Pathogenic: Capable of causing disease.

Pathogenic Organisms: Organisms, including bacteria, viruses, or cysts, capable of causing diseases (typhoid, cholera, dysentery) in a host (such as a person). There are many types of organisms which do NOT cause disease. These organisms are called nonpathogenic.

Pathogens: Microorganisms that can cause disease in other organisms or in humans, animals, and plants. They may be bacteria, viruses, or parasites and are found in sewage, in runoff from animal farms or rural areas populated with domestic and/or wild animals, and in water used for swimming. Fish and shellfish contaminated by pathogens, or the contaminated water itself, can cause serious illnesses.

Pathology: The study of disease.

Peak Operating Flow: The maximum rate of flow under which a treatment unit is designed to properly function and produce a certain quality product water.

Peracetic Acid: (CH₃COOOH) A strong oxidizing liquid used in a proprietary one percent solution with hydrogen peroxide as an effective sanitizer and disinfectant for both cellulosic and thin-film composite reverse osmosis membranes. Can be made by reaction of acetic acid (vinegar, CH₃COOH) and hydrogen peroxide (H₂O₂^–) with a sulfuric acid catalyst.

Percent Recovery: The percentage of the feedwater which becomes product water. Determined by the number of gallons (or liters) of product water divided by the total gallons (or liters) of feedwater and multiplied by 100. The percent recovery is called recovery rate in reverse osmosis and ultrafiltration.

Percent Rejection: (reverse osmosis/ultrafiltration) The percentage of TDS in the feedwater that is prevented from passing the membrane with the permeate. The formula used is: the difference obtained from the TDS in feedwater minus TDS in permeate divided by TDS in feedwater; then multiply the answer obtained by 100 to obtain a percent.

Percent Saturation: The amount of a substance that is dissolved in a solution compared with the amount that could be dissolved in the solution, expressed as a percent. Amount of substance that is dissolved divided by the amount that could be dissolved in solution X 100 percent.

Percolating: Water that passes through soil or rocks under the force of gravity.

Percolation: 1. The slow seepage of water into and through the ground.
2. The slow passage of water through a filter medium.

Performance Evaluation Sample: A reference sample provided to a laboratory for the purpose of demonstrating that the laboratory can successfully analyze the sample within limits of performance specified by the Agency. The true value of the concentration of the reference material is unknown to the laboratory at the time of the analysis.

Periphyton: Microscopic plants and animals that are firmly attached to solid surfaces under water such as rocks, logs, pilings, and other structures.

Peristaltic Pump: A self-priming pump that achieves pumping action by moving a system of rollers against a flexible tube. The pumped fluids (e.g., chemical feeds) are never exposed to the air or to the mechanical moving parts. The roller design prevents siphoning by providing a constant seal on the pumping tube.

Perlite: A volcanic glass metallic alloy that is composed of a carbide of iron, cementite (Fe₃C), and a ferric oxide compound, fernite (e.g., NaFeO₂), that are combined in proportions that yield the lowest melting point of this metal combination. Forms a lightweight and porous aggregate when expanded by heat which, in powdered form, can be used as the thin uniform coating on the septum in precoat filtration.

Permeability: 1. The ability of a body, such as a reverse osmosis or ultrafiltration membrane, to pass a liquid under pressure or to pass ions under the influence of an electric current as an ion exchange membrane in electrodialysis.
2. The ability of rock or soil to transmit water.

Permeate: 1. To penetrate and pass through, as water penetrates and passes through soil and other porous materials.
2. That portion of the feedwater which passes through a membrane to become product water.

Permissible Dose: The dose of a chemical that may be received by an individual without the expectation of a significantly harmful result.

Permselectivity: The ability of a semipermeable membrane to also be an ion exchanger and to allow selective passage of anions or cations under the influence of an electric current. Permselectivity is a term often used in relation to electrodialysis.

Permutit Process: An older term for the cation exchange method of water softening.

Peroxide: 1. Any compound containing the two oxygen atoms united together into a bivalent -O-O- group. Readily releases abnormally active atomic oxygen, and therefore any peroxide is a strong oxidizing agent.
2. Hydrogen peroxide.

Peroxone Process: A water treatment process in which ozone is exposed to ultraviolet light or hydrogen peroxide as it is being applied to the water. This advanced oxidation process (AOP) initiates the formation of highly reactive hydroxy radicals to achieve a higher level and range of oxidations.

Persistence: The resistance to degradation as measured by the period of time required for complete decomposition of a material.

Pesticide: Any substance or chemical designed or formulated to kill or control weeds or animal pests.

Petroleum Derivatives: Chemicals formed when gasoline breaks down in contact with groundwater.

Pharmaceutical Grade Water: The collective term for six types of water as defined by the U.S. Pharmacopeia:
1. purified water;
2. water for injection;
3. bacteriostatic water for injection;
4. sterile water for inhalation;
5. sterile water for injection; and
6. sterile water for irrigation.

Pharmacokinetics: The dynamic behavior of chemicals inside biological systems; it includes the processes of uptake, distribution, metabolism, and excretion.

Phase: A term used in general chemistry to refer to a particular homogeneous form (solid, liquid, or gaseous) of a substance which might exist in other forms or phases. For example, ice is the solid phase of water.

Phenolic Compounds: Organic compounds that are derivatives of benzene.

Phenolphthalein: An acid-base indicator which has no color in acid solution but turns pink to red as the solution becomes alkaline.

Phenolphthalein Alkalinity: The alkalinity in a water sample measured by the amount of standard acid required to lower the pH to a level of 8.3, as indicated by the change in color of phenolphthalein from pink to clear. Phenolphthalein alkalinity is expressed as milligrams per liter equivalent calcium carbonate.

Phosphate: A salt of phosphoric acid. In the water industry, polyphosphates are used as sequestering agents to control iron and hardness, and as coating agents to control corrosion by formation of a thin passivating film on metal surfaces. The complex phosphates also are a group of sequestering agents widely used in detergent formulations (except where phosphates are banned by law) because of their superiority in chemical water softening, sequestering, and other builder functions. Sodium tripolyphosphate was the original builder upon which modern laundry detergent technology developed, and is used in laundry granules, automatic dishwasher detergents, and cleansers. It is adaptable to the spray drying process by which granules are made. Tetrasodium pyrophosphate is also used in detergent granules, but since it does not rank as high in overall performance as sodium tripolyphosphate, its application is more limited. Highly soluble tetrapotassium pyrophosphate is used in liquid laundry detergents and in hard surface cleaners, where it serves as a builder, water softener, and source of alkalinity. Another complex phosphate, sodium metaphosphate, is marketed as a packaged water softener. The most widely used sodium metaphosphate is sodium hexametaphosphate (SHMP), which softens by sequestering. The orthophosphate form of phosphates, trisodium phosphate (also called sodium orthophosphate), is a water softener that inactivates hardness minerals by precipitation. It is used to a limited extent in soap and detergent formulations as a builder, as a source of alkalinity, and for its water-softening properties. It is also used in powdered hard surface cleaners and cleansers to supply alkaline cleaning power. Chlorinated trisodium phosphate is a dry chlorine bleach that, in water, acts much like sodium hypochlorite (liquid chlorine bleach). It provides a means of incorporating chlorine bleach effectively in dry products, and for this reason is used in cleansers and automatic dishwasher detergents. It also provides alkalinity that aids in cleaning. Waters containing concentrations of iron, manganese, calcium, or magnesium sometimes can be treated with a sequestrant such as polyphosphate and kept from depositing these mineral precipitates or scales for a period of time. However, polyphosphate sequestering is not permanent, and therefore may not be as effective as actually removing the iron, manganese, and hardness minerals, as is done with iron filters and ion exchange water softening, for example. The sequestering value of polyphosphates is destroyed when they revert (hydrate) to orthophosphate. Polyphosphate reversion or hydration to orthophosphate occurs naturally in water with time. Intentions would be for this reversion not to happen and not to drop the sequestered water hardness, iron, and manganese out until after it reaches the wastewater. But, the polyphosphate reversion process can be accelerated by various uncontrolled conditions, such as low pH, high temperature, and the presence of the oxides of certain heavy metals, including iron, calcium, copper, and zinc in water. It is important in phosphate feed water treatment operations to:
1) maintain a stable pH within the phosphate product’s performance rage.
2) determine the polyphosphate composition or blend that is most compatible with the specific water quality objectives and conditions, and
3) apply the appropriate dosage of phosphate to accomodate the system demand. Because of the difficulty in maintaining phosphate stabilities in the presence of varying pH, time, temperature, and metal oxides in most natural water supplies, the actual removal of iron, manganese, and water hardness is generally a more assuredly effective water treatment method. Municipal applications of polyphosphates to water supplies can interfere with home water treatment technologies. A portion of any water hardness, iron,

Phosphorus (P): A nonmetallic element which is essential to life. However, too much phosphorus in a body of water can cause excessive growth of plant life, which can create a lack of oxygen as the plants die and decay.

Photon: The basic unit (quantum) of electromagnetic radiation. Light waves, gamma rays, x-rays, and so on consist of photons. Photons are discrete concentrations of energy that seem to have no rest mass and move at the speed of light. Their nature can be described only in mathematical terms. Photons are emitted when electrons move from one energy state to another, as in an excited atom. SEE ALSO gamma decay; radiation.

Photosynthesis: The chemical process by which green plants make carbohydrates (which the plants use as food) from carbon dioxide and water in the presence of sunlight and chlorophyll. Oxygen is released as a byproduct of photosynthesis.

Phreatophyte: A type of plant with very long roots and extensive root systems which draws its water from the water table or other permanent groundwater supplies. Examples of phreatophytes are willow and salt cedar. Excessive growths of phreatophytes are undesirable in areas where water is scarce since they can consume large quantities of water.

Physical Stability: A measure of the ability of an ion exchanger or a filter medium to resist breakdown caused by the physical forces such as crushing, attrition, or high temperatures to which it is subjected during use.

Physical Water Treatment Device: A device that modifies the properties of water by physical means as opposed to chemical or mechanical means. Physical water treatment devices do not use, nor do they impart significant levels of chemical substance(s) to the water stream being treated. This class of device includes those that reduce or prevent certain scale deposits that are normal to hard water behavior.
They may provide a measurable reduction in hardness depending on the measurement method applied by conversion of calcium and magnesium ions to a precipitate form, but do not provide a reduction of total calcium or magnesium content of the treated stream nor have they been proven to achieve soft water. Physical water treatment devices use a range of processes, including media-induced precipitation, magnetic, electronic, electrostatic, and electromagnetic technologies.

Phytoplankton: Small, usually microscopic plants (such as algae), found in lakes, reservoirs, and other bodies of water.

Pico (p): A prefix used in the metric system to mean one-trillionth or 10^-12 or 0.000000000001.

Picocurie (pCi): A measure of radioactivity. One picocurie of radioactivity is equivalent to 0.037 nuclear disintegrations per second, or to 0.037 becquerels (Bqs).

Pilot Testing: Pilot testing usually refers to a pilot plant which is a trial intermediate between laboratory bench testing and full scale-operation in the field. Pilot testing is often conducted on-site in the field with a scaled down replica of the full-scale treatment plant.

Plan View: A diagram or photo showing a facility as it would appear when looking down on top of it.

Plankton: 1. Small, usually microscopic, free-floating plants (phytoplankton) and animals (zooplankton) in aquatic systems.
2. All of the smaller free-floating, suspended, or self-propelled organisms in a body of water.

Plastic: Any high polymer, usually synthetic, material that during its manufacture or processing can be extruded, molded, cast, drawn, or laminated into objects of all sizes and shapes by application of heat or pressure, by chemical condensation, or by casting during polymerization of monomers, and that can retain the new shape under conditions of use.

Plastic Pipe: Tubing or pipe made from unreinforced thermoplastic polymers such as polyethylene, polybutylene, polyvinyl chloride, chlorinated polyvinyl chloride, and polypropylenes, and from reinforced thermosetting polymers such as epoxides and polyesters with glass fibers as reinforcing to increase strength. Plastic pipe is characteristically flexible to rigid, lightweight, and strong; it resists attack by chemicals, corrosion, and weathering.

Plug Flow: A flow pattern in which the water being processed passes through the medium (such as a granular filter or an ion exchange bed) in a “piston-like” fashion instead of in turbulent or mixed flow patterns such as are found in other processes like ultraviolet light disinfection and electrodialysis.

Plumes: The way polluted water extends downstream from the pollution source (analogous to smoke from a smokestack as it drifts downwind in the atmosphere).

Pneumatic: Powered or moved by air pressure or compressed air.

Pneumatic Tank: A pressurized holding tank which is part of a closed water system (such as for a household well system) and is used to create a steady flow of water and avoid water surges created by the pump kicking on and off.

Point Source: A stationary location or fixed facility from which pollutants are discharged or emitted. Also, any single identifiable source of pollution, e.g., a pipe, ditch, ship, ore pit, factory smokestack.

Point Source: A stationery location or fixed facility from which pollutants are discharged or emitted. Also, any single identifiable source of pollution, e.g., a pipe, ditch, ship, ore pit, factory smokestack.

Point-of-Entry (POE) Treatment: Full service water treatment applied to the water entering a house or building for the purpose of reducing contaminants in the water distributed throughout the house or building (outside faucets may be excepted from treatment).

Point-of-Use(POU) Treatment: Water treatment applied to a single tap used for the purpose of reducing contaminants in water at that one outlet. POU treatment is often used to treat water for drinking and cooking only.

Polarize: As relates to electricity and corrosion control, to disrupt the corrosion process by developing a barrier on an anodic or cathodic surface.

Pole Shader: A copper bar circling the laminated iron core inside the coil of a magnetic starter.

Polisher: A treatment stage placed at the end of other treatment to bring the water to a more highly conditioned and more perfect state. For example, a mixed bed of ion exchange media installed as the final treatment step in the deionization process to remove last traces of undesirable ions.

Polishing Filter: A filter installed for use after the primary water treatment stage to remove any traces of undesirable matter or to polish the water.

Pollutant: A contaminant existing at a concentration high enough to endanger the environment or the public health or to be otherwise objectionable.

Pollution: Generally, the presence of matter or energy whose nature, location, or quantity produces undesired environmental effects. Under the Clean Water Act, for example, the term is defined as the man-made or man-induced alteration of the physical, biological, and radiological integrity of water.

Polyamide: A molecular chain polymer made of amide (-CONH-) linkages. Proteins of plants such as soybeans, peanuts, and corn are natural polyamides. Nylon is example of a synthetic polyamide. Thin-film composite reverse osmosis membranes are constructed of a thin layer of an aromatic polyamide extruded onto a less dense polysufone substrate.

Polybutylene (PB): A thermoplastic polymer, such as butyl rubber, of a butylene liquefied petroleum gas — isobutene, butene-1, or butene-2; manufactured in various degrees of elasticity, strength, and stability. Used for films, coatings, pipes, tubing, fittings, and many other services.

Polycarbonate: A thermoplastic polymer resin that is a linear polyester of carbonic acid. Polycarbonate is a transparent, nontoxic, noncorrosive, heat resistant, high impact strength plastic; it is generally stable, but may be subject to attack by strong alkalies and some organic hydrocarbons. It can be molded, extruded, or thermoformed, and is commonly used for numerous services, such as non-breakable windows, household appliances, tubing, piping, and cartridge filter sumps.

Polyelectrolyte: A polymeric electrolyte (natural or synthetic) with a long chain-like structure and a high molecular weight which may be used as a cationic, anionic, or nonionic flocculent (or coagulant aid) in the treatment of potable water. Often called a polymer.

Polyethylene: A tough thermoplastic polymer (-CH₂CH₂-) of ethylene that resists chemicals and absorbs very little moisture. Polyethylene can vary from soft and flexible to hard and rigid depending on the pressures and catalysts used during manufacturing. Low density polyethylene has its melting point at about 240 degrees Fahrenheit and tensile strength of 1500 psi; high density polyethylene melts at 275 degrees Fahrenheit and has tensile strength of 4000 psi. Among services, polyethylene is commonly used for tubing and piping, food packaging, garment bags, and molded plastic products.

Polymer: A chemical formed by the union of many monomers (a molecule of low molecular weight). Polymers are used with other chemical coagulants to aid in binding small suspended particles to larger chemical flocs for their removal from water. All polyelectrolytes are polymers, but not all polymers are polyelectrolytes.

Polyphosphate: Any of a broad familiy of inorganic phosphorus compounds that are commonly referred to as molecularly dehydrated phosphates or condensed phosphates, including hexametphosphate, tripolyphosphate (P₃O₁₀^5-), and pyrophosphate (P₂O₇^5-), among others. Unlike orthophosphate (PO₄^3-), for which four oxygen atoms always surround a single central phosphate, polyphosphates are arranged as polymeric chains or occasionally rings that vary in their phosphorus-to-oxygen ratio and chain length with different commercial formulations. Polyphosphate is used as a sequestering agent to control iron and hardness, and as a coating agent that forms a thin passivating film on metal surfaces to control corrosion. Polyphosphates in solution are anionic and may be removed from water with anion exchange resins. However, polyphosphates that have reacted with a metal (e.g., iron) can form a sticky colloidal precipitate that must be filtered to be removed from water. Inorganic polyphosphates may tend to breakdown (hydrolyze) into orthophosphate groups plus molecules of shortened chain length over time and under extreme temperature and pH conditions. Upon breakdown these phosphate compounds can drop out any sequestered metal ions, such as iron and hardness, allowing them to precipitate from the water.

Polypropylene: A thermoplastic polymer of propylene resembling polyethylene and used for making molded and extruded plastic products such as water pipe, tubing, and fittings.

Polystyrene: Polymerized styrene. Polystyrene forms the skeletal structure of most common ion exchange resin beads.

Polysulfone: A synthetic thermoplastic polymer. Used in the manufacture of ultrafiltration membranes and in thin-film composite and charged polysulfone reverse osmosis membranes.

Polyvinyl Chloride (PVC): A thermoplastic polymer resin material (-CH₂CHCl-) that is rigid and practically chemically inert. Commonly used for water pipes and fittings, as well as numerous other services such as siding, gutters, raincoats, chemical containers, flooring, toys, tennis court surfaces, and films and package coatings for food containers.

Polyvinylidene Fluoride (PVDF): A thermoplastic fluorocarbon polymer that can be used for injection molded or extruded products. More highly inert and resistant to oxidative degradation than polypropylene plastic, for example, but not as inert as the tetrafluoroethylene (TFE) fluorocarbon polymers (Teflon).

Population Equivalent: A unit of measure used to express the strength of waste water from any source. (That is, not from household waste water only.) In making such calculations, 0.17 pounds of BOD (biological oxygen demand) per capita per day is often used as the standard figure. Thus, waste water with 17 pounds of BOD per day would have a population equivalent of 17 divided by 0.17 or 100 people.

Population at Risk: A population subgroup that is more likely to be exposed to a chemical, or is more sensitive to a chemical, than is the general population.

Pore Volume: The volume of pores in a unit weight of media particles or filter bed.

Pores: Very small open spaces in a rock or granular material, including the complex network of channels in the interior of a particle, such as those within an ion exchange resin bead or an activated carbon granule.

Porosity: A measure of the volume of pores in a material. Porosity is calculated as a ratio of the interstices of a material (e.g., the volume of spaces between the media particles in a filter bed) to the volume of its mass, and is expressed as a percentage.

Porous: Full of pores through which water, light, etc. may pass.

Portable Exchange (PE) Tanks: Tanks containing up to two cubic feet of ion exchanger products or filter media are rented to homeowners or business clients with the beds fully-regenerated and ready for use. Portable exchange tanks do not have the valving controls required for regeneration. Upon exhaustion (determined by predetermined calendar days, meter, or monitoring device), the tanks are returned to a central regeneration plant where the resin or other media in each tank is reprocessed and restored for reuse. Portable exchange tanks may be available with water softening or deionization resins, mixed ion exchange media, manganese zeolite, activated alumina, and activated carbon. Portable exchange tanks are used for both household and commercial applications.

Positive Charge: The electrical potential of an atom which has lost one or more electrons, therefore leaving it with more protons than electrons. Cations carry positive charges.

Positive Displacement Pump: A type of piston, diaphragm, gear, or screw pump that delivers a constant volume with each stroke. Positive displacement pumps are used as chemical solution feeders.

Positron: An antiparticle whose mass and spin are the same as those of an electron, but with an opposite (positive) electric charge of equal magnitude. In the nucleus of an atom, a proton can be transformed to a neutron via emission of a positron-a process known as beta-plus radioactive decay. SEE ALSO antiparticle; beta decay.

Postchlorination: The application of chlorine to a water following other water treatment processes.

Potable (Drinking) Water: A water supply which meets USEPA and/or state water quality standards and that is considered safe and fit for human consumption.

Potassium Chloride (KCl): A colorless potassium salt which can be used as a regenerant in cation exchange water softeners and dealkalizers.

Potassium Cycle: The use of potassium chloride salt instead of sodium chloride salt in the regeneration of cation ion exchange water softeners. The potassium ion (K⁺) becomes the exchangeable ion rather than the sodium ion (Na⁺) in the sodium cycle system.

Potassium Permanganate: (KMnO₄) Dark purple, odorless crystals (with a blue metallic sheen) that dissolve in water to produce a purple-red color. Potassium permanganate is a powerful oxidizing agent that is used in water treatment as both an oxidizer and a disinfectant. It is also an effective regenerant for manganese oxidizing filters.

Potency: Amount of material necessary to produce a given level of a deleterious effect.

Potentiation: The effect of one chemical to increase the effect of another chemical.

Potentiometric Surface: The level to which water will rise in cased wells or other cased excavations into aquifers, measured as feet above mean sea level.

Pounds Per Square Inch (psi): Unit of measure for expressing pressure.

Pounds Per Square Inch Gauge (psig): Pressure measured with respect to that of the atmosphere. This is a pressure gauge reading in which the gauge is adjusted to read zero at the surrounding atmospheric pressure. It is commonly called gauge pressure.

Power Factor: The ratio of the true power passing through an electric circuit to the product of the voltage and amperage in the circuit. This is a measure of the lag or load of the current with respect to the voltage.

Prechlorination: The application of chlorine to a water supply prior to other water treatment processes which may follow.

Precipitate: 1. As a verb: to cause a dissolved substance to form a solid which comes out of solution and can be removed by settling or filtering. For example, the reduction of dissolved iron by oxidation, precipitation and filtration.
2. As a noun: the solid formed when a dissolved substance comes out of solution in such a way that it can be settled or filtered out.
3. As a verb: to cause moisture to condense and be deposited as rain, sleet, snow, etc.

Precipitation: 1. The process by which atmospheric moisture falls onto a land or water surface as rain, snow, hail, or other forms of moisture.
2. The chemical transformation of a substance in solution into an insoluble form (precipitate).

Precision: The ability of an instrument to measure a process variable and to repeatedly obtain the same result. The ability of an instrument to reproduce the same results.

Precoat: The application, usually by slurry, of a very fine granular filter medium such as diatomaceous earth to a retaining membrane or fabric surface prior to a service run. Precoating makes the medium unfit for further use. At the end of each service run, the precoat medium is rinsed off and disposed of prior to application of a new precoat to the filter septum.

Precursor: Compounds which lead to other compounds. For example, natural humic and fulvic acids which, upon combination with chlorine, lead to trihalomethanes.

Preplumbed Installation: An installation which allows domestic water treatment equipment to be easily installed because the necessary bypass and valves are already in place. An example would be a new home that already has all of the plumbing needed for installing a water treatment device.

Prescriptive: Water rights which are acquired by diverting water and putting it to use in accordance with specified procedures. These procedures include filing a request to use unused water in a stream, river, or lake with a state agency.

Preservative: An agent that prevents the deterioration of materials; usually associated with the prevention of biological deterioration.

Pressure Control: A switch which operates on changes in pressure. Usually this is a diaphragm pressing against a spring. When the force on the diaphragm overcomes the spring pressure, the switch is actuated (activated).

Pressure Differential: The difference in the pressure between two points in a water system. The difference may be due to the difference in elevation and/or to pressure drop resulting from water flow.

Pressure Drop: 1. A decrease in the water pressure (in psi) which occurs as the water flows. Pressure drop may occur for several reasons: internal friction between the molecules of water, external friction between the water and the walls of the piping system, or rough areas in the channel through which the water flows.
2. The difference between the inlet and outlet water pressure during water flow through a water treatment device such as a water conditioner. Abbreviated P and measured in pounds per square inch gauge pressure.

Pressure Head: The vertical distance (in feet) equal to the pressure (in psi) at a specific point. The pressure head is equal to the pressure in psi times 2.31 ft/psi.

Pressure Swing Adsorption (PSA): A process using a molecular sieve material, when pressurized to just overy 30 psig, to adsorb nitrogen and moisture from air, and to concentrate oxygen in air to approximately 80 to 95 percent oxygen, as in the air feed to an ozone generator.

Pretreatment: Any water treatment step performed prior to the primary treatment process, such as filtration prior to deionization.

Prevalence Study: An epidemiological study which examines the relationship between diseases and exposures as they exist in a defined population at a particular point in time.

Primacy: The responsibility for ensuring that a law is implemented, and the authority to enforce a law and related regulations. A primacy agency has the primary responsibility for administrating and enforcing regulations such as “primary enforcement responsibility” as defined in the Safe Drinking Water Act.

Primary Element: An instrument that measures (senses) a physical condition or variable of interest. Floats and thermocouples are examples of primary elements. Also called a sensor.

Primary Treatment: 1.n The first major treatment in a wastewater treatment works, consisting usually of sedimentation.
2. The removal of a substantial amount of suspended matter but little or no colloidal and dissolved matter.

Prime: The action of filling a pump casing with water to remove the air. Most pumps must be primed before startup or they will not pump any water.

Prior Appropriation: A doctrine of water law that allocates the right to use water on a first-come, first-serve basis.

Process Variable: A physical or chemical quantity which is usually measured and controlled in the operation of a water treatment plant or an industrial plant.

Process Water: Water used in a manufacturing or treatment process or in the actual product manufactured. Examples would be water used for washing, rinsing, direct contact, cooling, solution makeup, chemical reactions, and gas scrubbing in industrial and food processing operations. In many cases, water is specifically treated to produce the quality of water needed for the process.

Product Staging (reverse osmosis): The practice of using some of the product water from the first stage of RO treatment as feedwater for the second stage.

Product Water: Water that has been through the total treatment process and meets the quality standards required for the use to which the water will be put. Product water is called by different names, depending upon which treatment process it has gone through: “Centrate” from a centrifuge “Distillate” from a distiller “Filtrate” from a filter unit “Finished” from a municipal treatment plant “Deionized” from a cation and anion exchange system “Softened” from a softener unit “Permeate” from a reverse osmosis or ultrafiltration unit.

Product Water Dispensing Rate: That amount of product water available from the full-open dispensing outlet of a water treatment unit for a specified period of time.

Production Rate: The amount (gallons or liters) of product water the system produces per minute or (especially for reverse osmosis) per 24-hour period.

Profile: A drawing showing elevation plotted against distance, such as the vertical section or side view of a pipeline.

Prospective Study: An epidemiological study which examines the development of disease in a group of persons determined to be presently free of the disease.

Protease: A group of enzymes that is effective in breaking down proteins into smaller, less complex molecules.

Prototype: An original water treatment equipment unit on which a specific equipment line is modeled.

Protozoa: Microscopic, usually single-celled microorganisms which live in water and are relatively larger in comparison to other microbes. Protozoa are higher on the food chain than the bacteria that they eat. Many protozoa are parasitic. Singular form: protozoan or protozoon.

Prussian Blue: A blue paste or liquid (often on a paper-like carbon paper) used to show a contact area. Used to determine if gate valve seats fit properly.

Public Water System: A system for the provision to the public of piped water for human consumption, if such system has at least 15 service connections or regularly serves an average of at least 25 individuals daily at least 60 days out of the year. Such term includes:
1. any collection, treatment, storage, and distribution facilities under control of the operator of such system and used primarily in connection with such system; and
2. any collection or pretreatment storage facilities not under such control which are used primarily in connection with such system. A public water system is either a “community water system” or a “noncommunity water system.”

Pumice: Porous volcanic rock.

Pumicite: A stable, natural, glassy aluminum silicate mineral from volcanic ash which is used as a water treatment filtration medium.

Pumping Station: Mechanical devices installed in sewer or water systems or other liquid-carrying pipelines that move the liquids to a higher level.

Pumping Water Level: The vertical distance in feet from the center line of the pump discharge to the level of the free pool while water is being drawn from the pool.

Pure Water: This term has no real meaning unless the word “pure” is defined by some standard. The Water Quality Association Promotion Guidelines recommend against the use of the words “Pure Water” in advertising unless the meaning of “pure” is very clearly explained for the consumer. The capacity of the words “pure”, “purification,” “purifier” and other derivatives of the word “pure” to mislead consumers is considerable. In an absolute sense, all available water contains an amount of some substances in addition to H2O. The context that is meant by use of these words should always be clearly and accurately defined.

Purified Water: Water produced from water meeting the USEPA standards for safe drinking water through treatment by distillation, reverse osmosis, deionization, or other processes and which meets United States Pharmacopoeia (USP) purity standards for “purified water” can be labeled as “purified.” These standards regulate pH, chloride, sulfate, ammonia, calcium, carbon dioxide, heavy metals, oxidizable substances, total solids, and bacteria. If water meeting the USP standard has been distilled, it can alternatively be labeled “distilled water.”

Purveyor: An agency or person that supplies water (usually potable water).

Putrefaction: Biological decomposition of organic matter, with the production of ill-smelling and tasting products, associated with anaerobic (no oxygen present) conditions.

Pyrite: Iron disulfide (FeS₂). A common mineral that has a bright metallic luster and a brass-yellow color. Also called iron pyrite or fool’s gold.

Pyrogens: Substances (often of unknown origin) that produce fever when introduced into the human body. Being chemically and physically stable, pyrogens are not necessarily destroyed by conditions that kill bacteria.

Pyrolusite: (MnO₂) Manganese dioxide mineral ore which is sold under several trade names. It is the most important ore of manganese and is usually of an iron-black or dark steel-gray color with a metallic luster. Pyrolusite has very effective capacity as an iron, manganese, and/or hydrogen sulfide sacrificial filter medium but is very heavy, requiring high backwash rates of 20 gallons or more per square foot of media surface area.

pH (pronounce as separate letters): The degree of the acidity or basicity of a solution as measured on a scale (“pH scale”) of 0 to 14. The midpoint of 7.0 on the pH scale represents neutrality–that is, a “neutral” solution is neither acidic nor basic. Numbers below 7.0 indicate acidity; numbers above 7.0 indicate basicity. Substances that when dissolved in water cause the pH to be less than 7.0 often create a sour taste and may sting when in contact with skin. The resulting solution will turn litmus paper red. Substances that when dissolved in water cause pH to be greater than 7.0 create a bitter taste and a slippery feel and will turn litmus paper blue. Water with a high pH tends to cause drying of the skin.
More specifically, pH is the negative of the base 10 logarithm of the hydrogen ion concentration of a solution, -log₁₀[H⁺], where “p” is the short hand notation for “-log₁₀”. The hydrogen ion concentration, [H+], is the moles of hydrogen ions per liter of solution. In neutral water, for example, the hydrogen ion concentration is 1×10^-7 mol/L; the pH is therefore 7. Because both letters in the term pH are representative notations, the term must be written with a lower case “p” and an upper case “H”.
pH is an exponential function. A pH of 10 is ten times as basic as a pH of 9 and one hundred times as basic as a pH of 8. Similarly, a pH of 2 is one hundred times as acidic as a pH of 4 and one thousand times as acidic as a pH of 5.
In the field, pH is measured with a pH meter, which must be properly calibrated for accuracy. As pH in a water sample can change with time due to fluctuation of carbon dioxide concentration, pH should be measured quickly after sample collection.

pK: A measure of the completeness of an incomplete chemical reaction, using a logarithmic scale. Also used to express the extent of dissociation of weak acids and complex ions. The weaker the electrolyte, the larger is its pK. The strengths of different acids may be compared by using pK values. Mathematically speaking, pK is the negative of the logarithm of the ionization (dissociation) constant (pKeq) of a chemical compound.

ppb: Parts per billion.

ppm: Parts per million.

ppt: Parts per trillion.

psi: Pounds per square inch.

psig: Pounds per square inch gauge.

Qualification Test: Tests and verifications performed to validate water treatment equipment conformance to a specific standard.

Qualitative: Descriptive of kind, type, or direction, as opposed to size, magnitude, or degree.

Quantitative: Descriptive of size, magnitude, or degree.

Quartz Jacket: A clear, pure fused quartz tube used to protect the high intensity ultraviolet lamps in ultraviolet systems. It usually retards less than 10 percent of the ultraviolet radiation dose.

Quaternary Ammonium: An organic chemical group of cationic surface active compounds that tend to take up and hold on to surfaces of other substances; the group consists of ammonium (NH4) compounds in which one or more of the hydrogen atoms attached to the nitrogen are substituted by organic radicals. Quaternary ammonium compounds are strong bases, and their salts (formed by reaction with acids) provide the exchange sites on certain anion exchange resins. Quaternary ammonium salts in which the “active” ingredient is sufficiently high in activity and concentration can be used in water treatment as microbiocides (microbe killers) and surfactants. Cationic quaternary ammonium compounds adsorb the cell membranes of the microbes and react chemically with the negative charges carried by the cell walls to inactivate and kill the microorganism.

Quicklime: A material that is mostly calcium oxide (CaO) or calcium oxide in natural association with a lesser amount of magnesium oxide. Quicklime is capable of combining with water to form hydrated lime.

RO: Reverse Osmosis

Rad: A unit of absorbed dose of ionizing radiation, corresponding to 100 ergs of energy per gram of absorbing material. In the International System (SI) of Units, the rad is replaced by the gray (Gy); one gray (Gy) = 100 rads.

Radial Flow: The flow pattern in which water flows from the outside of a filter element to the center core. For example, a replaceable cartridge filter unit is often designed for radial flow.

Radial To Impeller: Perpendicular to the impeller shaft. Material being pumped flows at a right angle to the impeller.

Radical: 1. A group of atoms acting as a single atom which go through chemical reactions without being changed.
2. Some examples are bicarbonate (HCO3-); hydroxide (OH-); sulfate (SO4–). Free radicals contain one or more unpaired electrons and are usually short-lived and highly reactive.

Radioactive Fallout: Airborne particles of radioactive nuclei which result from nuclear explosions and settle out of the atmosphere, usually thousands of miles away from the place of detonation.

Radioactive Waste: Water or any other materials including spent nuclear reactor fuel, work clothes, or tools that contain radioisotopes.

Radioactivity: Emissions of radiant atomic energy (alpha, beta, and/or gamma rays) from some elements (radium, radon, uranium, thorium, etc.) caused by the spontaneous disintegration of the nuclei of the atoms of these elements.

Radionuclide: Any man-made or natural element which emits radiation in the form of alpha or beta particles, or as gamma rays.

Radium (Ra): Naturally-occurring radioactive elements (radium 226 and radium 228) created in the decay of the uranium and thorium series. Radium can be removed from water by cation exchange softening.

Radon (Rn): A colorless, odorless, short-lived radioactive gas which is produced by decay of the uranium/radium series and is soluble in water. Radon is considered carcinogenic when inhaled by humans. Radon can be removed from water by aeration or activated carbon.

Rainwater Catchment: AKA Rainwater Harvesting is the deliberate containment of rain or other natural precipitated water with the intention of controlled discharge or beneficial use in potable or non-potable applications. The relatively low mineral content of rainwater makes it highly desirable for reuse when properly processed for safety. Controlled discharge of harvested rainwater can be beneficial in storm water pollution control and energy harvesting. SEE ALSO potable water.

Range: The spread from minimum to maximum values that an instrument is designed to measure.

Ranney Collector: This water collector is constructed as a dug well from 12 to 16 feet (3.5 to 5 m) in diameter that has been sunk as a caisson near the bank of a river or lake. Screens are driven radially and approximately horizontally from this well into sand and the gravel deposits underlying the river.

Rated Capacity: As relates to softening or ion exchange, rated capacity, as stated by the manufacturer, may refer to any of several figures, all of which are given in relation to the period between regenerations:
1. the expected number of days the equipment will be in service;
2. the expected number of gallons of product water delivered; or
3. the grains of total hardness removed.
The capacity of an ion exchange system will vary, within limits, with the amount of regenerant used.     In filtration or adsorption applications, the manufacturer’s statement regarding the expected number of days the equipment will be in service or the expected number of gallons of product water delivered before it is expected that backwashing and rinse down should occur.

Rated Capacity: Rated capacity, as stated by the manufacturer, may refer to any of several figures, all of which are given in relation to the period between regenerations:
1. the expected number of days the equipment will be in service;
2. the expected number of gallons of product water delivered; or
3. the grains of total hardness removed. The capacity of on ion exchange system will vary, within limits, with the amount of regenerant used.

Rated Capacity: The manufacturer’s rated service cycle statement regarding the expected number of days the equipment will be in service or the expected number of gallons treated water delivered between servicing of the media (cleaning, regeneration, or replacement), as determined by testing or as specified by the manufacturer.

Rated In-Service Life: The total gallons (as specified by the manufacturer) of treated water delivered, or the length of time (based on water flow rates) the unit will be in operation before servicing (regenerating, cleaning, or replacement) of the treatment unit is expected to be necessary.

Rated Pressure Drop: In softening or filtration applications, rated pressure drop is the expected pressure drop in psi as stated by the equipment manufacturer or obtained under test conditions. Rated pressure drop is based on rated service flow rate for clean water at 60 degrees Fahrenheit using a freshly regenerated softener or a backwashed filter. The general limit is 15 psi at the specified service flow rate for the unit.

Rated Service Flow: The manufacturer-specified maximum and minimum flow rates at which a particular piece of water treatment equipment will continuously produce the desired quality of water.

Rated Softening Capacity: The statement by the water softener manufacturer about the expected number of grains per gallon of total hardness (as calcium carbonate equivalent) that will be removed between regenerations at the specified flow rate using the specified amount of regenerant (usually sodium chloride). The capacity of ion exchanger resin to remove hardness increases, within limits, with higher regeneration salt dosages; therefore, rated softener capacity must be related to the pounds of salt required for each regeneration.

Raw Water: A tank or reservoir in which water treatment chemicals are allowed residence time to react with contaminants in the water; hydraulic or mechanical mixing to ensure thorough distribution, and internal piping or baffles to inhibit short-circuiting of the water flow may be provided.

Reaeration: The introduction of air through forced air diffusers into the lower layers of the reservoir. As the air bubbles form and rise through the water, oxygen from the air dissolves into the water, and replenishes the dissolved oxygen. The rising bubbles also cause the lower waters to rise to the surface where oxygen from the atmosphere is transferred to the water. This is sometimes called surface reaeration.

Reagent: A pure chemical substance that is used to make new products or is used in chemical tests to measure, detect, or examine other substances.

Reagent-Grade Water (ASTM): Very high purity water produced to meet the standards outlined in the American Society for Testing and Materials (ASTM), Designation D 1193-77. Four grade levels, Types I through IV, are specified and three levels of maximum total bacterial count, Types A through C, are listed depending upon intended use. Reagent grade water is used for chemical analysis and physical laboratory testing.

Recarbonation: A process in which carbon dioxide is bubbled into the water being treated to lower the pH. The pH may also be lowered by the addition of acid. Recarbonation is the final stage in the lime-soda ash softening process. This process converts carbonate ions to bicarbonate ions and stabilizes the solution against the precipitation of carbonate compounds.

Receiver: A device which indicates the result of a measurement. Most receivers in the water utility field use either a fixed scale and movable indicator (pointer) such as pressure gauge or a movable indicator like those used on a circular-flow recording chart. Also called an indicator.

Receiving Waters: All distinct bodies of water that receive runoff of waste water discharges, such as streams, rivers, ponds, lakes, and estuaries.

Receptor: In biochemistry: a specialized molecule in a cell that binds a specific chemical with high specificity and high affinity. In exposure assessment: an organism that receives, may receive, or has received environmental exposure to a chemical.

Recharge: Process by which rainwater (precipitation) seeps into the groundwater system.

Recharge Area: Generally, an area that is connected with the underground aquifer(s) by a highly porous soil or rock layer. Water entering a recharge area may travel for miles underground.

Recharge Rate: The quantity of water per unit time that replenishes or refills an aquifer.

Reciprocal: Inversely or oppositely related. For example, 1,000 ohms of resistance is the reciprocal of 1/1,000 siemens (formerly mhos) of conductance.

Recirculation: 1. In water treatment system design, the continuous operation of the transfer pump to keep water flowing through the system (especially through the disinfection component) at a rate above the water use rate in order to reduce the hazard of bacterial growth.
2. In cross flow membrane filtration systems, the recycling of a portion of the reject stream to maintain a desirable flow across the membrane while the system is in operation.

Reclaimed Brine: That portion of a previously-used brine solution used to regenerate a batch of cation resin for portable exchange softener tanks. Brine which still measures at least 30 percent saturation and is low in total hardness can be reused in the first stages of the next cation batch regeneration.

Recorder: A device that creates a permanent record, on a paper chart or magnetic tape, of the changes of some measured variable.

Redox: A shortened term for “oxidation-reduction”. Used in terms such as “redox reactions” and “redox conditions”.

Reducing Agent: Any substance, such as base metal (iron) or the sulfide ion (S^2-), that will readily donate (give up) electrons. The opposite is an oxidizing agent.

Reduction: Reduction is the addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound. Under anaerobic conditions (no dissolved oxygen present), sulfur compounds are reduced to odor-producing hydrogen sulfide (H₂S) and other compounds. The opposite of oxidation.

Reference: A physical or chemical quantity whose value is known exactly, and thus is used to calibrate or standardize instruments.

Refractory: Resistant, under ordinary or various extraordinary conditions, to treatment or to change in chemical structure, such as resisting or being capable of enduring high temperatures without breaking down or decomposing.

Regenerant: In ion exchange or softening applications, a regenerant is the chemical solution used to restore an exhausted bed of ion exchange resin to the fully ionic (regenerated) form necessary for the desired ion exchange to again take place effectively. Regenerants are also used in a similar fashion to restore catalyst (e.g., iron and manganese removal) media for reuse. Sodium chloride brine is normally used to regenerate cation exchange water softeners and for some dealkalizer systems. Hydrochloric and sulfuric acids are used for hydrogen-form cation deionizations units. Sodium hydroxide is normally used to regenerate OH- form anion deionizations systems. Potassium permangante regenerant is used to regenerate a manganese greensand iron and manganese removal filter.

Regeneration: In ion exchange applications, the use of a chemical solution (regenerant) to displace the contaminant ions deposited on the ion exchange resin during the service run and replace them with the kind of ions necessary to restore the capacity of the exchange medium for reuse. This process is also called recharging or rejuvenation. Catalyst media are recharged similarly.

Regeneration Cycle: The several steps including backwash, application of regenerant, dilution, and fresh or deionized water rinse necessary to accomplish regeneration of an ion exchange bed or oxidizing filter.

Regeneration Level: The quantity of regenerant, usually expressed in pounds per cubic foot of ion exchanger bed or pounds per regeneration, used in the regeneration cycle of an ion exchange system. Regeneration level may also be called salt dosage.

Regeneration Tanks: Large vessels, either gravity (open) or pressurized (closed), in which batches of ion exchange resin used in portable exchange tanks are recharged. Some filter media such as manganese zeolite are also reprocessed in this manner.

Regeneration Water: All of the water consumed in the regeneration steps: backwash, regeneration (brining), dilution, and rinse. Raw water or partially-treated water may be used for the rinse down.

Reject Staging: A method used to raise the production rates of a reverse osmosis system by using the reject water from the first stage as the feedwater for the second or succeeding stage in the RO process.

Reject Water: A term used in distillation, electrodialysis, reverse osmosis, and ultrafiltration to describe that portion of the incoming feedwater that has passed across the membrane but has not been converted to product water and is being sent to the drain. Also called brine, concentrate, or retentate.

Rejection: In cross flow (membrane) filtration and distillation applications, the prevention by the membrane of the passage of total dissolved solids and other contaminants into the product water.

Rejection Rate: In a reverse osmosis or ultrafiltration system, rejection rate is
1. the quantity of the feedwater that does not pass through the membrane expressed as a percent of the total quantity of incoming feedwater; or
2. the concentration of contaminants that do not pass through the membrane as a percent of the total concentration of those particular contaminants in the feedwater.

Relative Density: The ratio of the density of a specific substance to the density of another substance which is used as a standard. The standard for comparison with liquids is pure water at 4 degrees Celsius. The standard for gases is air at normal temperature and pressure. Relative density was formerly called specific gravity.

Removable: Capable of being taken away from a water treatment equipment unit using only simple tools such as a screwdriver, pliers, or open-end wrench. Readily removable indicates capable of being taken away from a water treatment unit without the use of tools.

Renal: Pertaining to the kidney.

Renalin: Commercially available hydrogen peroxide in a 24 to 1 dilution. Used as a disinfectant/sanitizer for reverse osmosis and ultrafiltration membranes and other water treatment equipment.

Repeat Compliance Period: For public water system regulation, any subsequent compliance period after the initial compliance period.

Representative Sample: 1. A portion of water or material that is, as nearly as possible, identical in content and consistency to that in the larger body of water or material being sampled.
2. In water treatment equipment manufacturing and testing, a typical production line sample that exhibits the essential features corresponding to and equivalent to (within plus or minus 10 percent) the other production units of that model.

Reserve Capacity: The amount of further contaminant reduction or length of time a device can continue to operate at a high level of performance after a signal of upcoming exhaustion is triggered.

Reservoir: Any natural or artificial holding area used to store, regulate, or control water.

Residential Equipment: The term sometimes used to denote smaller-sized water processing equipment which has been designed primarily for home use and intermittent household water flow rates up to 12 gallons per minute. Water Quality Association equipment performance standards define residential equipment as that having an inlet designed to accommodate pipe size of no greater than one-inch internal pipe size (IPS) diameter. May also be referred to as domestic equipment or household equipment.

Residual: The amount of a specific material which remains in the water after the water has been through a water treatment step. Residual may refer to undesirable material remaining as the result of incomplete removal (called leakage) or to material that is meant to remain in the treated water, such as “residual chlorine.”

Residual Chlorine: Chlorine allowed to remain in a treated water after a specified period of contact time and to provide disinfection protection throughout the distribution system. The amount of residual chlorine is the difference between the total chlorine added and that consumed by the oxidizable matter.

Residual Disinfectant Concentration: C in CT calculations. The concentration of disinfectant measured in mg/L in a representative sample of water.

Residue: The dry solids remaining after the evaporation of a sample of water or sludge.

Resin: As used in the water processing industry, this term refers to ion exchange resin products which are usually specifically-manufactured organic polymer beads used in softening and other ion exchange processes to remove dissolved salts from water.

Resin Bead: In water processing, refers to the spherical shape of individual particles of ion exchange resin products, as compared to the irregular shaped particles of most other granular media products.

Resin Cleaner: One of several different chemical compounds used to cleanse ion exchange resin products of dissolved iron, aluminum, and various organics attracted to or bonded to the resin beads.

Resistance: That property of a material that resists the flow of an electric current. The standard unit of resistance is the ohm.

Respiration: The process in which an organism uses oxygen for its life processes and gives off carbon dioxide.

Retention: In membrane filtration, retention describes the minimum particle or molecule size retained by the membrane under a given set of conditions, namely, pressure, flux recovery, and temperature.

Retrospective Study: An epidemiological study which compares diseased persons with nondiseased persons and works back in time to determine exposures.

Reverse Deionization: The use of the anion exchange resin ahead of the cation exchange resin (the reverse of the usual order) in a deionization system.

Reverse Osmosis: A water treatment process that removes undesirable materials from water by using pressure to force the water molecules through a semipermeable membrane. This process is called “reverse” osmosis because the pressure forces the water to flow in the reverse direction (from the concentrated solution to the dilute solution) to the flow direction (from the dilute to the concentrated) in the process of natural osmosis. RO removes ionized salts, colloids, and organic molecules down to a molecular weight of 100. May be called hyperfiltration.

Reversible Effect: An effect which is not permanent, especially adverse effects which diminish when exposure to a toxic chemical is ceased.

Reversible Effect: An effect which is not permanent, especially adverse effects which diminish when exposure to a toxic chemical is ceased.

RfD (Reference dose): The daily exposure level which, during an entire lifetime of a human, appears to be without appreciable risk on the basis of all facts know at the time. Same as ADI.

Rill: A small channel eroded into the soil surface by runoff; rills easily can be smoothed out (obliterated) by normal tillage.

Rinse: In softening or ion exchange applications, the step in the regeneration process in which fresh water is passed through the bed of resin to remove any excess or spent regenerant prior to placing the softener into service.

Riparian Rights: A doctrine of state water law under which a land owner is entitled to use the water on or bordering his property, including the right to prevent diversion or misuse of upstream waters. Riparian land is land that borders on surface water.

Riser Pipe: As relates to well drilling, a steel pipe used in jet well drilling to carry water under pressure to the well point where unconsolidated material is loosened. In downflow ion exchange systems, the riser is the central (internal) pipe which carries the processed water from the bottom of the resin bed into the service lines or directs backwash water to the bottom of the ion exchanger bed. In countercurrent systems, it distributes the regenerant to the bottom of the bed for the upflow regeneration process.

Riser Pipe (ion exchange): In downflow systems, the riser is the central (internal)pipe which carriers the processed water from the bottom of the resin bed into the service lines or directs backwash water to the bottom of the ion exchanger bed. In countercurrent systems, it distributes the regenerant to the bottom of the bed fro the upflow regeneration process.

Riser Pipe (well drilling): A steel pipe used in jet well drilling to carry water under pressure to the well point where unconsolidated materials is loosened.

Risk: The potential for realization of unwanted adverse consequences or events.

Risk Assessment: A qualitative or quantitative evaluation of the environmental and/or health risk resulting from exposure to a chemical or physical agent (pollutant); combines exposure assessment results with toxicity assessment results to estimate risk.

Risk Characterization: Final component of risk assessment that involves integration of the data and analysis involved in hazard evaluation, dose-response evaluation, and human exposure evaluation to determine the likelihood that humans will experience any of the various forms of toxicity associated with a substance.

Risk Estimate: A description of the probability that organisms exposed to a specified dose of chemical will develop an adverse response (e.g., cancer).

Risk Factor: Characteristic (e.g., race, sex, age, obesity) or variable (e.g., smoking, occupational exposure level) associated with increased probability of a toxic effect.

Risk Management: Decisions about whether an assessed risk is sufficiently high to present a public health concern and about the appropriate means for control of a risk judged to be significant.

Risk Specific Dose: The dose associated with a specified risk level.

Rodenticide: Any substance or chemical used to kill or control rodents.

Rotameter: A device used to measure the flow rate of gases and liquids. The gas or liquid being measured flows vertically up a tapered, calibrated tube. Inside the tube is a small ball or bullet-shaped float (it may rotate) that rises or falls depending on the flow rate. The flow rate may be read on a scale behind or on the tube by looking at the middle of the ball or at the widest part or top of the float.

Rotary Drilling: A common hydraulic well-drilling method which uses a rotating drill pipe with a hard-tooled drill bit attached at the bottom. A fluid (drilling mud) is forced down through the drill pipe and then forced up again between the drill pipe and the well hole, carrying rock chippings (cuttings) up with the mud.

Rotor: The rotating part of a machine. The rotor is surrounded by the stationary (nonmoving) parts (stator) of the machine.

Route of Exposure: The avenue by which a chemical comes into contact with an organism (e.g., inhalation, ingestion, dermal contact, injection).

Runoff: That part of precipitation, snow melt, or irrigation water that runs off the land into streams or other surface water. It can carry pollutants from the air and land into the receiving waters.

Rust (Ferric Oxide): A reddish corrosion product occasionally found in water. Rust is formed as a result of electrochemical interaction between iron and atmospheric oxygen in the presence of moisture.

Rzynar Index: A modification of the Langelier index used to calculate the degree of calcium carbonate saturation and to predict the likelihood of scale formation from a water supply.

rem: The unit of dose equivalent from ionizing radiation to the total body or any internal organ or organ system. Equivalent dose (or the rem value) gives a measure of the biological harm caused by radiation exposure. A millirem (mrem) is 1/1000 of a rem. In the International System (SI) of Units, the rem is replaced by the sievert (Sv); one sievert (Sv) equals 100 rems.

SCFM: Cubic feet of air per minute at standard conditions of temperature, pressure, and humidity (0 degrees C/14.7 psia/50% relative humidity).

SDI: Silt Density Index.

SDWA: See Safe Drinking Water Act.

SEMI: Semiconductor Equipment and Materials International.

SI System of Units: The International System (SI) of units that was adopted and recommended for use in science and technology by the 11th General Conferece on Weights and Measures in 1960. This coherent system of units is built from the following seven SI base units: Physical Name of SI Unit Symbol for Quantity SI Unit length meter m mass kilogram kg time second s electric ampere A current thermodynamic kelvin K temperature amount of mole mol substance luninous candela cd intensity

SMCLs: Secondary Maximum Contaminant Levels. Secondary MCLs for various water quality indicators are established to protect public welfare.

SNARL: Suggested No Adverse Response Level. The concentration of a chemical in water that is expected not to cause an adverse health effect.

SOCs: synthetic organic chemicals.

Sacrificial Anode: An anode made of suitable metal placed in a water heater tank to protect the tank from corrosion. Anodes of metals such as aluminum, magnesium, or zinc are sometimes installed in water heaters and other tanks to control corrosion of the tank. The introduction of the anode creates a galvanic cell in which the magnesium or zinc will go into solution (be corroded) more quickly than the metal of the tank, thereby imparting a cathodic (negative) charge to the tank metal(s) and thus preventing tank corrosion. This corroding of the anode metal is called “the sacrifice of the anode”.

Safe: Condition of exposure under which there is a “practical certainty” that no harm will result in exposed individuals.

Safe Drinking Water Act (SDWA): The national legislation first passed by the U.S. Congress and signed into law by the President in 1974 and amended in 1986. The SDWA directs the U.S. Environmental Protection Agency to promulgate and enforce standards for safe drinking water necessary to protect public health at public water systems serving 25 or more people for an average of 60 days per year. The law also contains provision for delegating primary enforcement responsibility to states and for protecting underground sources of drinking water.

Safe Water: Water that does not contain harmful bacteria, or toxic materials or chemicals. Water may have taste and odor problems, color and certain mineral problems and still be considered safe for drinking.

Safe Yield: The annual quantity of water that can be taken from a source of supply over a period of years without depleting the source beyond its ability to be replenished naturally in “wet years.”

Sal Marina: Spanish name for sea salt.

Salimeter: A hydrometer which measures the percent of salt as NaCl in brine or other salt solutions. A 100 percent reading on a salimeter is about 26.4 percent salt by weight at 60 degrees F. Some people use the term “salinometer” to refer to a salimeter.

Saline: Consisting of, or containing, salt.

Saline Solution: Any solution with the total dissolved solids (TDS) usually ranging from 15,000 to 30,000 mg/L. For example, a solution of sodium chloride and water, usually containing other salts also. May also be called saline water.

Salinity: The relative concentration of dissolved salts, usually sodium chloride, in a given water. A measure of the concentration of dissolved mineral substances in water.

Salinometer: An instrument for determining the salt concentration (salinity) of brine water by measuring the electrical conductivity of the solution. A salinometer is sometimes called a salt gauge.

Salometer: See Salimeter.

Salt: 1.(chemistry) A chemical compound formed by the neutralization of an acid with a base. For example, H₂SO₄ (acid) + 2NaOH (base) = NaSO₄ (salt) + 2H₂O (water).
2. (water treatment) compounds such as sodium chloride (NaCl) or potassium chloride (KCl), both of which are used in solution to regenerate cation exchange water softeners and some dealkalizers.
3. common table salt, which is sodium chloride (NaCl).
SEE ALSO common salt (NaCl); rock salt; solar salt; water softener salt.

Salt Block: Evaporated salt or fine rock salt which is mechanically compressed into dense blocks, weighing about 50 pounds each, which are sometimes used in residential water softeners.

Salt Bridging: The creation of salt encrustment and cementing together of salt particles in dry storage brine tanks which causes tight bonding of the entire salt mass to the walls of the brine tank and prevents the salt from dropping into the incoming water for brine makeup.

Salt Cake: Sodium sulfate (Na₂SO₄) which is only 90-99 percent pure (i.e., contains 1-10 percent of substances other than Na₂SO₄). Salt cake is made by heating rock salt with sulfuric acid, producing muriatic acid and salt cake.

Salt Dosage: See Regeneration Level.

Salt Efficiency: In an ion exchange water softener, the hardness removal capacity calculated as grains of hardness removed divided by the weight of salt in pounds that is used to achieve that amount of hardness reduction. Operational salt efficiency refers to the salt efficiency performance of a water softener under conditions of actual or simulated long term use (six months or more) in a household where gallons of water usage typically varies from day to day.

Salt Mushing: See Mushing.

Salt Splitting: An ion exchange process in which neutral salts in water are converted to their corresponding acids or bases. A strong base anion exchanger resin can convert a salt solution to caustic (base) (for example, NaCl + ROH = RCl + NaOH); and a strong acid cation exchanger can convert a salt to acid (for example, NaCl + HR = NaR + HCl).

Salt Splitting Capacity: A regular test used on an ion exchange resin to determine the capacity of a used resin versus the standard rated capacity of the resin when fresh.

Salt Water: The general term for all water over 1,000 ppm (mg/L) total dissolved solids.
Fresh Water – <1,000 TDS
Brackish – 1,000-5,000 TDS
Highly Brackish – 5,000-15,000 TDS
Saline – 15,000-30,000 TDS
Sea Water – 30,000-40,000 TDS
Brine – 40,000-300,000+ TDS

Saltless (or salt free) Water Softener: SEE saltless water treatment device; water softener

Saltless (or salt free) Water Treatment Device: A device, product, or equipment using chemical, physical or any other means, to counteract scale buildup of hard water minerals (calcium and magnesium) without the use of salt for regeneration. Depending on the scale reduction or prevention method other effects of soft water may also be observed. SEE ALSO water treatment; water treatment device; water softener; water softening.

Saltless (or salt-free) Water Conditioner: Same as Saltless (or salt-free) Water Treatment Device.

Sand: Soil particles between 0.05 and 2.0 mm in diameter.

Sand Filter: The oldest and most basic filtration process, which generally uses two grades of sand (coarse and fine) for turbidity removal or as a first stage roughing filter or prefilter in more complex processing systems. Municipal water treatment systems often used gravity rapid-rate sand filters. Pressure-type sand filters plus coagulants are used for commercial applications. For home use or for small swimming pools, a pressure sand filter is also used.

Sand Trap: A mechanical device to separate fine sand or other abrasive material from water in wells with faulty screens. The hydrocyclone separator is one form of a sand trap.

Sanitary Sewer: A sewer that transports only waste waters (from domestic residences and/or industries) to a waste water treatment plant.

Sanitary Survey: An on-site review of the water source, facilities, equipment, operation, and maintenance of a public water system for the purpose of evaluating the adequacy of the facilities for producing and distributing safe drinking water.

Sanitization: The act of sanitizing. Sanitization is not an absolute phenomenon; it is a partial removal or inactivation of microorganisms. Depending on the system, a sanitization operation should reduce the viable organism population by 50 to 99.9 percent, but it should completely eliminate enteric pathogen-related organisms such as Salmonella and E. coli. (Disinfection by comparison, should reduce 99.9 to 99.9999 percent of viable microorganisms.)

Sanitize: To reduce the number of bacterial contaminants to safe levels as judged by public health requirements. To make clean and free or inactivation of dirt, filth, and conditions injurious to health. Generally considered to reduce germ count by 50 to 99.9 percent. The USEPA requires that sanitizing claims must show a 99.9 percent microbial reduction in five minutes.

Sanitizer: An agent that results in the reduction of bacterial numbers to accepted public health limits by sanitizing. Sanitizers are applied in the cleaning operations of inanimate objects.

Saprophytes: Organisms living on dead or decaying organic matter. They help natural decomposition of organic matter in water.

Saturated Solution: A solution which contains the maximum amount of the dissolved substance (solute) that a solution of this kind can normally hold at this temperature.

Saturated Zone: The area below the water table where all open spaces are filled with water.

Saturation: In water chemistry, means the state of a solution (water) when it holds the maximum equilibrium quantity of dissolved matter at a given temperature and pressure. The limit when no more of a given substance will dissolve.

Saturation Index: A scale showing the relationship of calcium carbonate to the pH and hardness of a given water. The saturation index is commonly used to determine the scale-forming tendency of a particular water.

Saturator: A device which produces a fluoride solution for the fluoridation process. The device is usually a cylindrical container with granular sodium fluoride on the bottom. Water flows either upward or downward through the sodium fluoride to produce the fluoride solution.

Scale: A coating or precipitate deposited on surfaces such as kettles, water pipes, or steam boilers that are in contact with hard water. Waters that contain carbonates or bicarbonates of calcium or magnesium are especially likely to cause scale when heated. Also called hard water scale.

Scavenger: In water treatment applications, a polymer matrix or ion exchanger that is used specifically to remove organic species from the feedwater before the water is to pass through the deionization process.

Schedule, Pipe: A sizing system of arbitrary numbers that specifies the I.D. (inside diameter)and O.D. (outside diameter) for each diameter pipe. This term is sued for steel, wrought iron, and some types of plastic pipe. Also used to describe the strength of some types of plastic pipe.

Screen Size: See Mesh Size.

Secchi: (SECK-key) Disc – A flat, white disc lowered into the water by a rope until it is just barely visible. At this point, the depth of the disc from the water surface is the recorded seechi disc transparency.

Secondary Treatment: As relates to waste water treatment, the process which makes up the second step in treating waste water and removes suspended and dissolved solids and biochemical oxygen demand (BOD) from the waste water which has already undergone primary treatment.

Secondary Drinking Water Regulations: See Drinking Water Standards.

Sediment Yield: The quantity of sediment arriving at a specific location.

Sedimentary Rock: Rock that results from the consolidation of layers of loose sediment made up of various kinds of organic and inorganic matter.

Sedimentary Rock: Rock that results from the consolidation of layers of loose sediment made up of various kinds of organic and inorganic matter.

Sedimentation: The process of suspended solid particles settling out (going to the bottom of the vessel) of water that has little or no movement. Sometimes sedimentation only occurs after the particles have begun to coagulate (either naturally or because of the use of a coagulant aid such as alum) into larger and heavier flocs.

Seepage: The percolation of water through the soil from unlined channels, ditches, water courses, and water storage facilities.

Seize Up: Seize up occurs when an engine overheats and a part expands to the point where the engine will not run. Also called “freezing.”

Selective Ion Exchanger: An ion exchange medium which shows selectivity. For example, a chelating ion exchange resin which will remove only gold ions from solution.

Selectivity: The tendency of an ion exchanger to “prefer” (have more attraction for) certain kinds of ions over others, as if the resin were ranking the types of ions in order to be removed: most preferred ion, second most preferred, etc.

Selectivity Band: The respective region or zone within an ion exchanger or adsorption medium bed where individual ions or substances accumulate and are removed from the water in order of their individual respective preferences for the medium. Because different substances each have different affinities or selectivity preference for the treatment medium, removal occurs in different zones of the medium bed. The zone for the ion or substance with the lowest selectivity will proceed through the bed first, and the zone for the highest selectivity substance will proceed through the bed last.

Seltzer Water: See Soda Water.

Semiconductor Equipment and Materials International (SEMI): The group which has set the electronics grade purified water standards.

Semiconfined Aquifer: An aquifer that is partially confined by a soil layer (or layers) of low permeability through which recharge and discharge can occur.

Semipermeable Membrane: See Membrane.

Sensor: An electrical or electronic device which measures the quality of the product water leaving the treatment cycle. A sensing meter which measures conductivity or resistivity (resulting from TDS) is used for deionization, electrodialysis and reverse osmosis. In a cation water softener, sensors used are either as:
electronic devices which measure hardness in effluent softened water, or probes which detect the slightly different electrical impedance between that caused by calcium/magnesium and sodium ions. The sensor is immersed in the resin bed and triggers regeneration.

Sensor: An electrical or electronic device which measures the quality of the product water leaving the treatment cycle. A sensing meter which measures conductivity or resistivity (resulting from TDS) is used for deionization, electrodialysis and reverse osmosis. In a cation water softener, sensors used are either as:
1. electronic devices which measure hardness in effluent softened water, or
2. probes which detect the slightly different electrical impedance between that caused by calcium/magnesium and sodium ions. The sensor is immersed in the resin bed and triggers regeneration.

Sepralator: A spiral-wound membrane element or cartridge used in cross flow membrane systems.

Sepsis: A diseased state caused by the presence of pathogenic microorganisms in the bloodstream.

Septage: The liquid and semisolid contents removed by pumping from a septic tank.

Septic: A condition produced by bacteria when all oxygen supplies are depleted. If severe, bottom deposits appear and water turns black, gives off foul odors, and the water has a greatly increased chlorine demand.

Septic System: An on-site system designed to treat and dispose of domestic sewage; a typical septic system consists of a tank that receives wastes from a residence or business and a system of tile lines or a pit for disposal of the liquid effluent that remains after decomposition of the solids by bacteria in the tank.

Septic Tank: A tank (usually underground) into which the solid matter of household sewage flows and is held for decomposition caused by bacteria. Septic tanks are common in rural areas where no municipal sewage system is available.

Septicemia: Bacteria multiplying in the bloodstream.

Sequential Actions: One action occurring after or followed by others in a given order–as opposed to simultaneous actions.

Sequester: To keep a substance (e.g., iron or manganese) in solution through the addition of a chemical agent (e.g., sodium hexametaphosphate) that forms chemical complexes with the substance. In the sequestered form, the substance cannot be oxidized into a particulate form that will deposit on or stain fixtures. Sequestering chemicals are aggressive compounds with respect to metals, and they may dissolve precipitated metals or corrode metallic pipe materials.

Sequestering Agent: 1. A chemical that forms complexes with metallic ions in solution so that the metallic ions may no longer be precipitated. For example, calcium soap precipitates are not produced from hard water treated with sodium hexametaphosphate. Note however, the tendency for condensed phosphate polymers, such as hexametaphosphates, may be to hydrate in water, especially under conditions of high temperature or high pH, and thereby revert to a more simple and stable phosphate form, such as orthophosphate which can no longer sequester the hardness and metal ions. 2. Any agent that prevents an ion from exhibiting its usual properties because of close combination with an added material.

Sequestration: A chemical reaction in which certain ions are bound into a stable water-soluble compound so that they (ions) are prevented from certain normal but undesirable actions. For example, the sequestration of iron to prevent it from oxidizing, precipitating, and staining. The same as sequestering. SEE ALSO chelation.

Serial Filtration: The arrangement of two or more filtering steps, one following the other, in order to remove increasingly finer particulates at each stage and provide for filtration of all sizes of suspended solids. Cartridge-style units often employ this method, using depth prefilters (compressed fibers) followed by surface filtration with a micromembrane cartridge element.

Service Flow: The rate in U.S. gallons per minute (gpm) or liters per minute (L/min) at which a given water processing system can deliver product water. The rating may be for intermittent peak flow or constant flow.

Service Line Sample: A one-liter sample of water collected in accordance with CFR Section 141.86(b)(3) of the code of Federal Regulations, that has been standing for at least six hours in a service line.

Service Pipe: The pipeline extending from the water main to the building served or to the consumer’s system.

Service Run: That portion of the operating cycle of a water processing system during which the water is actually being treated. The other portion of the cycle is regeneration. For example, that portion of the cycle in which the hard water supply is passed through a regenerated and rinsed bed of ion exchange material, thereby producing soft water.

Service Unit: A term most often applied to portable exchange tanks.

Sessile: Attached firmly to a permanent base and not free to move about. Bacteria grow and multiply faster when attached (sessile) in water systems, than when free-floating (planktonic) in water. Attached sessile cells form a larger colony; their polysaccharide containing glycocalyx slime layer helps adhere other bacteria cells and nutrients which float past and also acts as a protective layer which resists chemical disinfectant penetration. This sessile microbial colonization is known as biofilm in water systems.

Set Point: The position at which the control or controller is set. This is the same as the desired value of the process variable.

Sewage: The combination of liquids or water carrying wastes from homes, businesses, institutions, and industries. In some cases, storm water, groundwater, and surface water may be included in the sewage flow. In the larger sense, sewage is the water supply of a community after the water supply has been used.

Sewer: An underground system of conduits (pipes and/or tunnels) that collect and transport waste waters and/or runoff; gravity sewers carry free-flowing water and wastes; pressurized sewers carry pumped waste waters under pressure.

Sewerage System: The network of sewers that carries sewage from point of origin to point of treatment.

Shallow Well: A well sunk in easily-penetrated ground to a point which is below the water table but usually less than about 30 feet in depth.

Shearing Action: The action of low temperature water flowing at high rates which splits and separates particle agglomerations and prevents the formation of floc deposits during the coagulant feed/filtration process. This action may also tear away from the filter any previous deposits or suspended matter.

Shielding: The separation and insulation of metal parts of a pipe joint by a special fitting which will not conduct electric current. The fitting prevents corrosion caused by galvanic action between two different metals. Shielding can also be a protective cover or barrier that prevents transmittance of heat or radiation to or from a component of water treatment equipment.

Shock Load: The arrival at a water treatment system of raw water containing unusual amounts of algae, colloidal matter, color, suspended solids, turbidity, or other pollutants.

Short Circuiting: A condition that occurs in tanks or basins when some of the water travels faster than the rest of the flowing water. This is usually undesirable since it may result in shorter contact, reaction, or settling times in comparison with the theoretical (calculated) or presumed detention times.

Siemens (S): Formerly called mho. The siemens (S) is the SI unit of conductance equal to the reciprocal of the ohm.

Sievert (Sv): The SI unit of ionizing radiation dose equivalent. One sievert (Sv) equals 100 rems.

Silica: As used in water chemistry, a collective term encompassing all reactive (dissolved) and inert (nonreactive and undissolved or colloidal) forms of the chemically resistant dioxide SiO₂of silicon, or silicates formed from silicon and oxygen in combination with one or more other minerals or metals. Silica, such as quartz for example, is present in almost all earth’s minerals, rocks, soils, sands, and clays. It is found in fresh water in a range of 1 to 100 mg/L. In a laboratory water analysis report, silica is nearly always identified as silicon dioxide (SiO₂), however when dissolved in water silica is actually hydrated to silicic acid (SiO₂nH₂O) and associated anions. Below a pH of 9, silica is present mostly in the silicic acid form (SiO₂ 2H<sub>2</sub>O, also written as H₄SiO₄. At low pH, silicic acid can polymerize or condense to form uncharged colloid particles (known as colloidal silica) as small as 0.02 microns in size. As the pH of water exceeds 8, silicic acid (H₄SiO₄) increasingly dissociates into the bisilicate anions H₃SiO₄^– and H₂SiO₄^2-. This will increase the solubility of the silica unless divalent and polyvalent cations are available in significant concentrations. These cations of calcium, magnesium, iron, and aluminum, for example, will likely cause precipitation of insoluble silicate salts, especially at higher pH levels. The precipitation of multivalent cations with the silicates tends to occur at a pH value of 1 to 2 points below the point at which the cation hydroxide solubilities would be exceeded. Silicates can interfere with the crystal growths of precipitating metal and mineral cations thereby keeping such silicate complexed particulates in the colloidal size ranges, e.g., silicates are a contributor to formations of colloidal iron and colloidal manganese. Below pH 8, dissolved silica in the silicic acid form (H₄SiO₄) precipitates to SiO₂ when the solubility of silicic acid is exceeded. Precipitated silica and silicates can be very difficult to redissolve. Silica concentrations above 100 mg/L in reverse osmosis waste streams (concentrate water) may cause silica deposition which will foul the membrane, however because silica is slow to crystalize some RO systems can operate safely with silicic acid concentrations as high as 140 mg/L in the RO concentrate without experiencing silica scale formation. The potential for silica precipitation should be evaluated whenever silica is present in an RO feedwater at a concentration above 20 mg/L. Silica is also objectionable in boiler feedwater because it may form a tenacious scale in the boiler itself, and because it volatilizes at high temperatures and redeposits on turbine blades. High concentrations of silica are likewise a concern in cooling tower makeup water because of the characteristic uncertainty about silica’s solubility limits. Inorganic silicate compounds, such as soluble sodium silicates (the simplest form of glass, known as water glass) have been employed for more than 70 years to treat water. These silicates are anodic corrosion inhibitors that will combine (react with) the free metal released at the anode site of corrosion activity in copper, lead, cast iron and ferrous metals, steel, galvanized steel, bronze, red and yellow brass, and nickel alloys, to form an insoluble metal-silicate compound which seals off the corrosion site. Relatively high dosages, 25 to 50 mg/L, of silicate are required during the first 30 to 60 days of treatment. This should form the initial protective coating for corrosion control. Thereafter, the silicate dosage is reduced incrementally to maintenance feeds in the 4 to 10 mg/L range. There are reports of preferences of sodium silicate corrosion inhibitors for successful treatment of low alkalinity and

Silicates: A group of compounds containing oxygen and silica(SiO₂). Silicates are considered anodic corrosion inhibitors combining with the free metal released at the anode site of corrosion activity and forming an insoluble metal-silicate compound. Silicates can also be used to sequester soluble iron and manganese present in source water to help prevent oxidation and the formation of red and black water.

Silt: Soil particles between 0.05 and 0.002 millimeter in approximate diameter.

Silt Density Index (SDI): A test used to measure the level of suspended solids in feedwater for membrane filtration systems. The test consists of the time it takes to filter 500 milliliters of the test water through a 47-millimeter diameter, 0.45 micron rated microporous filter under a constant pressure of 30 psig. The SDI of feedwater to a reverse osmosis membrane should be maintained at less than 5, preferably less than 3.3. SDI = 100 (1-t₁/t₂)/T where: t₁ = time to filter 500 mL of water initially, t₂ = time to filter 500 mL of water after T minutes (T is usually 15 minutes.)

Simulate: To reproduce the action of some process, usually on a smaller scale.

Single Family Structure: A building constructed as a single-family residence that is currently used as either a residence or a place of business.

Single-Stage Pump: A pump that has only one impeller. A multistage pump has more than one impeller.

Single-Stage Recirculation: (reverse osmosis) Process used in a multiple (2-6) membrane reverse osmosis system in which a portion of the concentrate stream is split off and routed back to the inlet and mixed with the feedwater. This increases the flow across the membrane without increasing the amount of feedwater and increases the overall recovery rate. The pump capacity will affect the amount of water to be recirculated and the recovery rate.

Single-Stage System: (reverse osmosis) A reverse osmosis system in which the water is passed through the membrane(s) only once by using a single high-pressure pump.

Sink: A place in the environment where a compound or material collects.

Slake: To react calcium oxide (lime or quicklime) with water to form calcium hydroxide (slaked or hydrated lime) plus heat.

Slope: The slope or inclination of a trench bottom or a trench side wall is the ratio of the vertical distance to the horizontal distance or “rise over run.”

Slotted Lateral Pipes: Underdrain lateral pipes which have many tiny openings (as though they had been partially cut around the perimeter with a hacksaw) instead of orifices (drilled 1/4 in. or 3/16 in. holes.)

Sloughing: The action of a medium (filter, ion exchanger, or membrane) casting off into the effluent stream any substance intended for removal from the water. Sloughing may be caused by shearing action or by ion selectivity.

Slow Rinse: 1. (ion exchange) That portion of the rinsing stage which usually follows the introduction of the regenerant and during which the rinse water (deionized, decationized, softened, or untreated water) passes through the resin at the same flow rate as the regenerant;
2. (filtration) The initial rinse down after application of regenerant for resettling the medium bed. After the bed is resettled, a final fast rinse is used to “purge” the bed.

Slow Sand Filtration: A process involving passage of raw water through a bed of sand at low velocity (generally less than 0.4 m/h) resulting in substantial particulate removal by physical and biological mechanisms.

Sludge: The settleable solids separated from water during processing.

Slug: A temporary abnormally high concentration of an undesirable substance which shows up in the product water. A slug is generally a symptom of a malfunction of the water processing unit. For example, a “slug” of iron-rust might appear due to the shearing action of a high-demand flow which loosens a previously deposited iron precipitate.

Slurry: A watery mixture or suspension of insoluble (not dissolved) matter; a thin watery mud or any substance resembling it (such as a grit slurry or a lime slurry).

Small Bore Piping: Copper or stainless-steel pipe with a small diameter of 0.5 inches or 15 mm. Such pipe is commonly found in pump-assisted hot water central heating systems.

Soap: The water-soluble reaction product of a fatty acid ester and an alkali (usually sodium hydroxide) which produces suds when used with water for washing or cleaning purposes. Some soaps are mild disinfectants. Common soaps such as sodium and potassium soaps are soluble but can be converted to insoluble calcium and magnesium soap “curds” (bathtub rings) by the presence of hardness ions in the water.

Soap Curd: The insoluble precipitate that forms when soap is used in hard water. Soap curd and lime soap are synonymous

Soda Ash: (Na₂CO₃) A common water treatment chemical, sodium carbonate, which is used for pH modification, as an alkaline builder in some soaps and detergents, and in the lime-soda ash water softening process.

Soda Water: Water which has been impregnated with carbon dioxide (CO₂) so that it will be effervescent when not under pressure. Same as carbonated water, seltzer water, and sparkling water.

Sodium: (Na⁺) A metallic element found abundantly in compounds in nature, but never existing alone. Sodium compounds are highly soluble and do not form curds when used with soaps or detergents. Many sodium compounds are used in the water treatment industry. Most notable is the use of sodium chloride as a regenerant in the cation exchange water softening process.

Sodium Bicarbonate: (NaHCO₃) A mild alkali, commonly called baking soda. Sodium bicarbonate is used in powdered hard surface cleaners and some presoak formulations to provide alkaline cleaning at a controlled level.

Sodium Carbonate: (Na₂CO₃) A fairly strong alkaline salt occurring naturally as soda ash. A solution of sodium carbonate (soda ash) may be used with a simple proportionate chemical feed pump system to raise the pH of a water supply. Each mg/L of carbon dioxide in water requires a minimum of 2.5 mg/L of soda ash for neutralization. Sodium carbonate finds wide use as a builder in laundry detergents and as a source of alkalinity in powdered hard surface cleaners and presoak products. Sodium carbonate supplies alkaline cleaning power and also softens water by precipitating the hardness minerals out of solution. It is also called soda ash and is available on the retail market in a hydrated crystalline form under the name “washing soda.”

Sodium Chloride (NaCl): The chemical name for common table salt. Sodium chloride is also widely used for regeneration of ion exchange water softeners and in some dealkalizer systems.

Sodium Citrate: The sodium salt of citric acid. Sodium citrate sequesters hardness minerals and is used as a builder in some nonphosphate products. Its principal application is in liquid laundry detergents; it also is used in some presoak products.

Sodium Cycle: The cation exchange water softening process in which sodium ions in the resin are exchanged for hardness ions in the water. Sodium chloride is commonly used for resin regeneration.

Sodium Hexametaphosphate: A glassy sodium polyphosphate used as a sequestering, dispersing, deflocculating agent and as a coating agent to form a thin passivating film that protects metals from corrosion.

Sodium Hexametaphosphate: A substance that has a molecular ratio of 1.1 parts of sodium monoxide (Na₂O) to 1 part of phosphorus pentoxide (P₂O₅, with a guaranteed minimum of 76 percent P₂O₅. Several specialized compositions are available. It is also called sodium polyphosphate or glassy sodium phosphate, and is used as a sequestering, dispersing, deflocculating agent and as a coating agent to form a thin passivating film that protects metals from corrosion.

Sodium Hydrosulfite: (Na₂S₂O₄) A crystalline salt which is a strong reducing agent and the main ingredient in several resin cleansers that are used to clean iron-fouled ion exchange resin beds.

Sodium Hydroxide (NaOH): A strong alkaline compound used as a regenerant for anion exchange resin in deionization systems and for the pH modification of low pH (acid) water. Sodium hydroxide is also called caustic, caustic soda, or lye>.

Sodium Hypochlorite (NaOCl): Liquid bleach; used as a source of chlorine in water treatment. Laundry bleach available from grocery stores is 5.25 percent chlorine and commercial strength bleach available from swimming pool suppliers or chemical companies is usually 12.5 percent chlorine.

Sodium Metaphosphate: Any of several complex phosphates with excellent sequestering properties.

Sodium Silicate(s): (Na₂SiO₂ or SiO₂,Na₂) Glassy polymeric silicates used to prevent corrosion by formation of a thin passivating film on metal surfaces in boilers and other water systems.

Sodium Tripolyphosphate: (Na₅P₃O₁₀) A crystalline salt used chiefly as a water softener, sequestering agent, and deflocculating agent, especially in soaps and detergents.

Soft Water: Water which contains less than 1.0 grain per gallon (<17.1 milligrams per liter (mg/L) or parts per million (ppm)) of total hardness. SEE ALSO hard water; hardness.

Softened Water: Water which has been treated by any method that reduces its total hardness content to less than 1 gpg (17.1ppm). SEE ALSO hard water; zero soft water; soft water.

Software Programs: Computer programs; the list of instructions that tell a computer how to perform a given task or tasks.

Soil Erodibility: A measure of the soil’s susceptibility to raindrop impact, runoff, and other erosional processes.

Soil Profile: A vertical section of the earth’s highly weathered upper surface often showing several distinct layers or horizons.

Soil Sealant: A chemical or physical agent that plugs porous soils and prevents leaching or percolation.

Soil Sealant: A chemical or physical agent that plugs porous soils and prevents leaching or percolation.

Soil Structure: The arrangement of soil particles into aggregates.

Soil Texture: The proportions of soil particles (sand, silt, and clay) in a soil profile.

Solar Salt: Common salt which is produced by solar evaporation in shallow ponds or lagoons and used in water softener regeneration.

Solder: A metallic compound used to seal the joints between pipes. Until recently, most solder contained 50 percent lead. The use of lead solder containing more than 0.2 percent lead is now prohibited for pipes carrying potable water.

Sole Source Aquifer: An aquifer that supplies 50 percent or more of the drinking water of an area.

Solenoid: A magnetically (electrical coil) operated mechanical device. Solenoids can operate a small valve or a switch.

Solenoid Shutoff Valve: An electrical device operated by a magnetic coil to make the valve either open for flow or close to shut off water flow. This type of valve is used extensively for flow control and direction on many water processing systems.

Solids: (In water and waste water laboratory analyses) The matter dissolved or suspended in water or waste water.

Solute: The substance which is dissolved in the solvent (generally a liquid such as water) to form a solution.

Solution: A mixture in which one or more substances (solutes) are dissolved into another substance (solvent), usually a liquid, in such a way that the solute is equally distributed (homogeneous) throughout the solvent in the form of either molecules (as in a sugar solution) or ions (as in a salt solution).

Solvent: A liquid substance that dissolves another substance (the solute) to form a solution.

Sorption: A surface phenomenon which may be either absorption or adsorption, or a combination of the two; often used when the specific mechanism is not known.

Sounding Tube: A pipe or tube used for measuring the depths of water.

Sour Brine: Brine that contains a high concentration of calcium, magnesium, or other substances that would interfere with its use or reuse for effective regeneration of exhausted ion exchange resin.

Span: The scale or range of values an instrument is designed to measure.

Sparger: A perforated pipe in an aerator or ozone contact compartment through which the air or ozone-containing air is sprayed into the water, and which allows for the diffusion of the air or ozone into the water.

Specific Conductance: A rapid method of estimating the total dissolved solids (TDS) content of a water supply. Its measurement indicates the capacity of a sample of water to transmit an electrical current, which is associated with the concentration of ionized substances in the water. An alternate method is the measurement of specific (electrical) resistance. The unit of measure for specific conductance is siemens (formerly called mhos) per centimeter which is 1.0 divided by specific resistance. When the numbers get too small, the microsiemens (S) is used. For example, 100 mg/L of NaCl dissolved in water causes a specific conductance of 212 microsiemens per centimeter, whereas a 1,000 mg/L solution of NaCl in water would result in 2,000 microsiemens per centimeter. It is well known that pure water is a very poor conductor of an electric current. However, when ionizable compounds (salts, etc.) are dissolved in the water, the solution becomes a conductor of electric current. The nature of the ionized compound and the amount of it dissolved are responsible for the specific conductance (or specific resistance) of the solution. The more salts dissolved, the greater is the specific conductance.

Specific Gravity: Weight of a particle, substance, or chemical solution in relation to the weight of water. Water has a specific gravity of 1.000 at 4 degrees C (39 degrees F). Particulates in raw water may have a specific gravity of 1.005 to 2.5.

Specific Resistance: The capacity for resisting the flow of electrical current. In the case of liquids, such as water, specific resistance is the resistance of a 1.0-centimeter cube, which is the resistance offered by the liquid between two electrode plates 1 cm. square and placed 1 cm. apart. The unit of measure is ohms-centimeter, and specific resistance is the reciprocal of specific conductance. One hundred milligrams per liter of NaCl dissolved in water causes a specific resistance of 4,716 ohms-centimeter, whereas a 1,000 mg/L solution of NaCl in water would result in 500 ohms-cm.

Specific Yield: The quantity of water that a unit volume of saturated permeable rock or soil will yield may be expressed as a ratio or as a percentage by volume

Spectrometer: A chemical analytical instrument used in spectroscopy.

Spectroscopy: A technique used in chemical analyses which is based on the principle that many substances, when crossed by a beam of light, allow a unique and well-defined fraction of that light to pass or emit a well-defined fraction of radiation when returning from an atomic vapor state to their fundamental state. The characteristic wave length pattern of the absorbed or emitted light can be used to identify the particular substance with great certainty. The quantity of the light absorbed or emitted is proportional to the concentration of the substance. Spectroscopy is one of the most frequently used analytical methods for water analyses. Ultraviolet light (UV) spectroscopy (using light wave lengths between 10 and 390 nanometers) and infrared (IR) spectroscopy (using light wave lengths between 780 and 300,000 nanometers) are used particularly to identify and quantify organic molecules. Atomic absorption spectroscopy (AA) is used to identify and quantify inorganic elements. Spectroscopy is also called spectrometry and spectrophotometry.

Sphericity: The measure of the bead roundness or “whole bead” count of beads in an ion exchange resin product or other bead form absorbent or filter medium.

Spiral-Wound: A very common construction configuration for one style of reverse osmosis membrane and cartridge filter element. In RO membranes, the membrane sheets are assembled in layers around a perforated mandrel product water tube, with coarse mesh spacer screens between the layers, to form a complete module element. In cartridge filter elements, the filtration material, such as fiber cord, is continuously wound around a perforated mandrel core tube.

Split-Stream Treatment: The art of proportionally blending a stream of treated water with a stream of untreated water from the same source to achieve a lower measurement of a given contaminant in the blended stream, thus not removing all of the contaminant but still meeting the water quality desired, such as meeting a maximum contaminant level requirement for delivered water. Split-stream operation makes it possible to treat less than the full flow of water.

Spoil: Excavated material such as soil from the trench of a water main.

Spore: A small reproductive body, often single-celled, capable of reproducing the organism under favorable conditions. The spore is sometimes considered the resting stage of the organism. Among the organisms that may produce spores are algae, bacteria, and certain protozoans. In water, most spores resist adverse conditions which would readily destroy the parent organism.

Sporicide: An agent that destroys microbial spores. By definition, sterilizing agent.

Spring: A place where groundwater flows naturally from the soil or rock formation onto the land surface or into a body of surface water. A spring is sometimes used as a source of water for a shallow dug well.

Spring Line: Theoretical center of a pipeline. Also, the guideline for laying a course of bricks.

Spring Water: Water obtained from an underground formation from which water flows naturally to the surface or would flow naturally to the surface if it were not collected underground.

Stability: The ability of an ion exchange product or filter medium to withstand physical and chemical degradation in cycle-after-cycle operations.

Stainless Steel (ss): A chromium alloy with substantially 50 percent or more iron and usually with some nickel (typically 12 to 30 percent chromium and zero to 22 percent nickel) that is practically inert toward rusting and corrosion. The nickel content of ss contributes to improved corrosion resistance. Austenitic stainless steel contains 16 to 26 percent chromium, six to 22 percent nickel, low (less than 0.15 percent) carbon, and cannot be hardened by heat treatment; ferritic ss contains 15 to 30 percent chromium, low (0.1 percent) carbon, and cannot be hardened by heat treatment; martensitic ss contains 12 to 20 percent chromium, controlled carbon and other additives, and can be hardened by heat treatment which increases the tensile strength from 80,000 to 200,000 psi. = ADD TABLE HERE =

Standard: A physical or chemical quantity whose value is known exactly and is used to calibrate or standardize instruments.

Standard Industrial Classification (SIC): The statistical classification standard published by the United States Office of Management and Budget (OMB) that assigns an industry number to businesses and business units by type of economic activity. It is the classification standard underlying all establishment-based Federal economic statistics classified by industry type. The system uses from a one-digit to a four-digit classification number depending on how narrowly the business unit is defined. There are 11 one-digit groupings and over 1,000 four-digit groupings. Household and industrial water treatment equipment manufacturing, for example, is in SIC 3589, water conditioning service is in SIC 7389, distribution of water conditioning equipment is in SIC 5074, manufacturing of fluid power control valves is in SIC 3492, manufacturing of water treatment chemicals is in SIC 2899, manufacturing of distilled water is also in SIC 2899, manufacturing of pharmaceutical water or of water purification tablets is in SIC 2834, manufacturing of carbonated and flavored bottled water is in SIC 2086, bottling natural, spring, or mineral water is in SIC 5149, and retailing bottled water is in SIC 5499.

Standard Methods: A shortened title for the Standard Methods for the Examination of Water and Wastewater, a joint publication of the American Public Health Association, American Water Works Association, and the Water Pollution Control Federation. This widely-used volume outlines the procedures used to analyze water and waste water impurities and characteristics.

Standard Methods for the Examination of Water and Wastewater: A joint publication of the American Public Health association, American Water Works Association and the Water Pollution Contol Federation which outlines the procedures used to analyze the impurities in water and waste water.

Standard Sample: The aliquot of finished drinking water that is examined for the presence of coliform bacteria.

Standard Solution: A solution in which the exact concentration of a chemical or compound is known.

Standardize: To compare with a standard. In chemistry, to find out the exact strength of a solution by comparing it with a standard of known strength, or to set up an instrument or device to read a standard. This allows you to adjust the instrument so that it reads accurately or enables you to apply a correction factor to the readings.

Starch: Chemically, starch refers to complex carbohydrates obtained from vegetable sources. In home laundry usage, the term has been expanded to cover products that perform the same function as starch, i.e., supplying body or stiffness to fabrics, but that are based on synthesized chemicals such as carboxymethylcellulose or polyvinyl acetate. The latter are called synthetic or plastic starches. Vegetable starch comes as: dry, uncooked starch (lump, cube, or powder), which must be mixed with hot water or cooked before use; pre-cooked flakes, which can be mixed with cold water; a concentrated pre-cooked solution; and a concentrated solution in an aerosol container for spraying directly on fabrics while ironing. Synthetic or plastic starches come as liquids and in aerosol form for direct application. The liquids are available in soluble form, which is removed in the next laundering. More durable varieties last through several washes. Besides supplying body and stiffness, starch gives ironed articles a fresh smooth appearance, helps garments stay clean longer because of the harder, smoother surface, and facilitates soil removal in the next wash since the soil becomes imbedded in the starch, not the fabric.

Starters: Devices used to start up large motors gradually to avoid severe mechanical shock to a driven machine and to prevent disturbance to the electrical lines (causing dimming and flickering of lights).

State: The agency of the State or Tribal government which has jurisdiction over public water systems. During any period when a State or Tribal government does not have primary enforcement responsibility pursuant to Section 1413 of the Safe Drinking Water Act, the term “State” means the Regional Administrator, U.S. Environmental Protection Agency.

Static: Fixed in position; resting; without motion.

Static Head: When water is not moving, the vertical distance (in feet) from a specific point to the water surface is the static head. (The static pressure in psi is the static head in feet times 0.433 psi/ft.)

Static Pressure: The static pressure in psi is the static head in feet times 0.433 psi/ft. The static pressure in psi is the static head in feet times 0.433 psi/ft.

Static System: A system or process in which the reactants are not flowing or moving.

Static Water Depth: The vertical distance in feet from the center line of the pump discharge down to the surface level of the free pool while no water is being drawn from the pool or water table.

Static Water Level: The elevation or level of the water table in a well when the pump is not operating. The level or elevation to which water would rise in a tube connected to an artesian aquifer, or basin, or conduit under pressure.

Stator: That portion of a machine which contains the stationary (non-moving) parts that surround the moving parts (rotor).

Steady Operating Flow Rate: The flow in U.S. gallons per minute (or liters per minute) at which a water processing filter or ion exchanger will deliver its rated capacity. For water softeners, this flow is based upon delivering softened water from an incoming raw water of 20 grains per gallon total hardness as calcium carbonate.

Stepwise Regeneration: The method of regenerating ion exchange resin beds several times with the same regenerant, but at a higher concentration each time. The method is usually used to avoid calcium sulfate precipitation when sulfuric acid is employed as a regenerant for cation bed units of deionizer systems that are being used to decationize unsoftened feedwater.

Sterilization: The removal or destruction of all (or greater than 99.9999 percent of all) microorganisms, including pathogenic and other bacteria, vegetative forms and spores.

Sterilize: Complete (100 percent or at least greater than 99.9999 percent) destruction or inactivation of all living organisms. The USEPA requires that sterilization claims must demonstrate killing or inactivation of all microorganisms, including bacterial spores.

Stethoscope: An instrument used to magnify sounds and convey them to the ear.

Stochastic: Based on the assumption that the actions of a chemical substance results from probabilistic events.

Stoichiometric: Related to the proportions in which chemicals combine to form compounds and the weight relations in chemical reactions. Stoichiometry is the mathematical and theoretical study of how chemicals combine.

Stokes Law: A formula for calculating the rate of fall of particles through a liquid medium. The rate at which a spherical particle will rise or fall when suspended in a liquid medium varies as the square of the particle’s radius, as the density of the particle, and as the viscosity of the fluid.

Storage Capacity: The maximum volume of water available for use from the water storage tank, e.g., the amount available from a RO or distiller water storage tank.

Storage Tank: A compartment used to accumulate the product water from a water treatment unit so sufficient quantity and/or pressure is available for intermittent periods of higher flow rate water use.

Storm Sewer: A sewer that collects and transports surface runoff to a discharge point (infiltration basin, receiving stream, treatment plant).

Stratification: The formation of separate layers (of temperature, plant, or animal life) in a lake or reservoir. Each layer has similar characteristics such as all water in the layer has the same temperature.

Stratified Bed: In ion exchange applications, a bed in which two exchangers of different classes and different densities have been placed in the same column (bed), such as weak base anion resin on top of a strong base anion exchanger, or in cation exchange systems, a weak acid on top of a strong acid resin.

Stray Current Corrosion: Corrosion due to electrical current flowing through paths other than the intended circuit. This form of electrolysis causes corrosion independent of other environmental factors like pH and is proportional to the Amperage of the applied current. This type of corrosion typically causes a concentration of localized pitting. Stray current can originate from many sources, including: Cathodic protection systems, welding operations, improper grounding of radio transmitters, grounded DC electric sources, and faulty electrical appliances.

String Wound Element: A cartridge-style filter element constructed by continuous spiral winding of natural or synthetic yarn around a preformed product water tube core and then building it up in layers to form a depth-type filter element.

Strip Cropping: A crop production system that involves planting alternating strips of row crops and close-growing forage crops; the forage strips intercept and slow runoff from the less protected row crop strips.

Strong Acid Cation Exchanger: A cation exchange resin with an exchange site/active group (usually sulfonic) capable of splitting neutral salts (NaCl, MgSO4, Ca[NO3]2, etc.) to form their corresponding free acids (HCl, H2SO4, HNO3, etc.).

Strong Base Anion Exchanger: An anion exchange resin with an exchange site/active group [usually quaternary amine, -N(CH3)+++] capable of splitting neutral salts (NaCl, CaSO4, KNO3, etc.) to form their corresponding free bases (NaOH, Ca[OH]2, KOH, etc.).

Styrene: (C₈H₈) A fragrant, liquid, unsaturated hydrocarbon used chiefly in the manufacture of synthetic rubber, resins, and plastics. Styrene is the prime ingredient in many cation and anion exchange resins.

Subchronic: Of intermediate duration, usually used to describe studies or levels of exposure between five and 90 days.

Submerged Aquatic Vegetation (SAV): Aquatic vegetation, such as sea grasses, that cannot withstand excessive drying and therefore live with their leaves at or below the water surface. SAVs provide an important habitat for young fish and other aquatic organisms.

Submergence: The distance between the water surface and the media surface in a filter.

Submersible Pump: A pump designed to fit inside the well casing and to operate below the water level in a drilled well.

Submicron Filter: A cartridge-type membrane filter used in fine particle separation applications to remove particulates of less than one micron in size.

Suction Lift: The negative pressure [in feet (meters) of water or inches (centimeters) of mercury vacuum] on the suction side of the pump. The pressure can be measured from the center line of the pump down to (lift) the elevation of the hydraulic grade line on the suction side of the pump.

Sulfate Bacteria: Sulfate-reducing bacteria, such as Desulfovibrio, and the single-celled aerobic sulfur-oxidizers of the genus Thiobacillus. The sulfate-reducing bacteria contribute to tuberculations and galvanic corrosion of water pipes and to hydrogen sulfide taste and odor problems in water. Thiobacillus, by its production of sulfuric acid, has contributed to acid corrosion of metals.

Sulfonic Acid: (-SO₂OH) A specific acidic group which forms the exchange site active group in certain cation exchange resins and gives these resins their ion exchange capability.

Sulfur (S): A yellowish solid chemical element. “Sulfur” is also often used to refer to sulfur water.

Sulfur Water: Water containing objectionable amounts of hydrogen sulfide gas which causes an offensive “rotten egg” odor.

Sulfuric Acid: (H₂SO₄) A very strong, corrosive and hazardous acid used as a regenerant for the cation stage of an ion exchange deionization system. Sulfuric acid is also used occasionally to lower the pH of highly alkaline water. When higher concentrations of sulfuric acid are combined with high concentrations of calcium, calcium sulfate crystals precipitate and create tenacious fouling of media particles. An older name for sulfuric acid is oil of vitriol.

Superchlorination: The addition of excess amounts of chlorine to a water supply to speed chemical reactions or ensure disinfection within a short contact time. The chlorine residual following superchlorination may be high enough to be unpalatable, and thus dechlorination is commonly employed before the water is used.

Superfund: Federal law which authorizes USEPA to manage the cleanup of abandoned or uncontrolled hazardous waste sites.

Supernatant: Liquid removed from settled sludge. Supernatant commonly refers to the liquid between the sludge on the bottom and the water surface of a basin or container.

Supersaturated Solution: An unstable condition of a solution (water) in which the solution contains a substance at a concentration greater than the saturation concentration for the substance.

Supplier of Water: Any person who owns or operates a public water system.

Support Media Bed: Material of a specific graded particle size (such as gravel) used as a subfill to support the primary medium bed. In larger diameter systems (tanks), this bed improves the collection of processed water and promotes more uniform distribution of the backwashing water.

Surface Filtration: Filtration that occurs at the surface layer (as opposed to within the body depth) of the filter and is accomplished by passing the material to be filtered over a grating, screen, sieve, or membrane fabric with microsized holes. The size of the holes in the filter determines what materials will pass through and what will be filtered out (held back).

Surface Loading: One of the guidelines for the design of settling tanks and clarifiers in treatment plants. Used by operators to determine if tanks and clarifiers are hydraulically (flow) over- or underloaded. Also called overflow rate.

Surface Pump: A mechanism for removing water or waste water from a sump or wet well.

Surface Runoff: Precipitation, snow melt, or irrigation in excess of what can infiltrate the soil surface and be stored in small surface depressions; runoff is a major transporter of nonpoint source pollutants.

Surface Tension: The tendency of a liquid to form a relatively tough “skin” or film on its surface. Surface tension is caused by the attraction between the molecules of the liquid, and it is surface tension that causes water molecules to stick together and form drops. Surface tension makes it possible to float a razor blade on the surface of a glass of water even though the blade is much heavier than the water. The surface tension that holds the drops together makes it difficult for the water to penetrate or “wet” fabrics (or skin). Soaps and detergents contain “wetting agents” to reduce surface tension and increase fabric penetration by water.

Surface Water: All water naturally open to the atmosphere (rivers, lakes, reservoirs, streams, impoundments, seas, estuaries, etc.) and all springs, wells, or other collectors which are directly influenced by surface water.

Surfactant: A surface-active substance that when added to water lowers surface tension and increases the “wetting” capabilities of the water. Reduced surface tension allows water to spread and to penetrate fabric or other substances to be washed or cleaned. There are three categories of surfactants: detergents, wetting agents, and emulsifiers. “Surfactant” is a contraction for surface-active agent.

Surge Chamber: A chamber or tank connected to a pipe and located at or near a valve that may quickly open or close or a pump that may suddenly start or stop. When the flow of water in a pipe starts or stops quickly, the surge chamber allows water to flow into or out of the pipe and minimize any sudden positive or negative pressure waves or surges in the pipe.

Suspended Solids: Solids that either float on the surface or are suspended in water or other liquids, and which are largely removable by laboratory filtering. The quantity of material removed from water in a laboratory test, as prescribed in Standard Methods for the Examination of Water and Wastewater.

Sweet Brine: Brine that contains sufficient sodium or potassium content and is relatively low in calcium, magnesium, or other interfering substances such that it is effective for use or reuse in regenerating exhausted ion exchange resin.

Sweet Water: Fresh water. Palatable water. Not salt water.

Swelling: The expansion of certain ion exchange resins when converted into a specific ionic state. This is a reversible expansion, as the resin may well shrink as it becomes exhausted. Some exchangers will expand as they exhaust. Cation exchange water softening resins will generally swell when exhausted (loaded with hardness ions) and will shrink when regenerated with heavier salt dosages of 10 to 15 pounds of sodium chloride (NaCl) or potassium chloride (KCl) per cubic foot of resin. Standard cation softening resin (8 percent polystyrene/DVB), in the calcium form, will shrink about 5 percent in volume when treated with a 25 percent salt-brine solution.

Synergism: The combined action of several chemicals which produces a greater effect than would be obtained by simply adding together the effects produced by each chemical separately. Synergism is also called synergy.

Synthetic Detergent: A manufactured cleaning agent. Detergents can be classified as anionic, cationic, or nonionic.

Synthetic Organic Chemicals: Man-made organic substances including herbicides, pesticides, and various industrial chemicals and solvents. Synthetic organic chemicals are generally considered dangerous in drinking water at concentrations above the USEPA maximum contaminant levels. Often referred to as SOCs.

System: A complete integrated series consisting of various components and perhaps multiple water treatment processes which can be tested, installed, and operated as a singular unit of equipment. For example, a single RO treatment system generally consists of two or more stages of media filtration plus cross flow membrane filtration and water storage.

System with a Single Service Connection: A public water system which supplies drinking water to consumers via a single service line.

Systemic: Relating to whole body, rather than its individual parts.

Systemic Effects: Effects observed at sites distant from the entry point of a chemical due to its absorption and distribution into the body.

TDS: Total Dissolved Solids.

TDS Creep: The appearance of salt in RO product water which sometimes occurs as a result of the reduction of differential pressure across the membrane as can occur when the RO unit has been shut down for a period of time. Water flow will cease to permeate through the membrane when there is insufficient differential water pressure across the membrane. However TDS permeates through the membrane as a function of the TDS concentration difference across the membrane.

TFC: Thin-film Composite.

TH: Total Hardness.

THM Precursor: See Precursor.

THMs: See Trihalomethanes.

TNCWS: See Transient Water System.

TOC: Total Organic Carbon.

TS: Total solids

TSS: Total suspended solids

Tangential Flow Filtration: See Cross Flow Filtration.

Tannic Acid: See Tannin.

Tannin: Any of a group of water soluble, natural organic phenolic compounds that are produced by metabolism in trees andplants, and are part of the degredation-resistant fulvic acid materials formed during the decomposition of vegetation. Tannins occur in water in almost any location where large quantities of vegetation have decayed. Tannins can impart a faintly yellowish to brown color to water. Tannin molecules tend to form anions in water above pH 6 and can then be treated with anion exchange resins. Below pH 5, tannins are better treated with activated carbon.

Tansmittancy: The ability of water to trasmit or convey ultraviolet energy

Taste Threshold: The minimum concentration of a chemical or biological substance which can just be tasted.

Teflon: Trade name for a high temperature industrial plastic material used in cookware finishes, bearings, lubricating, plumbing sealants, and a practically inert coating on metal and glass surfaces.

Telemetry: The electrical link between the transmitter and the receiver. Telephone lines are commonly used to serve as the electrical line.

Temperature Sensor: A device that opens and closes a switch in response to changes in the temperature. This device might be a metal contact, or a thermocouple that generates minute electrical current proportional to the difference in heat, or a variable resistor whose value changes in response to changes in temperature. Also called a heat sensor.

Temporary Hardness: See Carbonate Hardness.

Tension: 1. Electric potential or voltage. The term usually is used to mean high voltage, as in “high tension transformer” or “high tension lines.”
2. Stretched to stiffness or tautness.

Teratogenesis: The introduction of nonhereditary congential malformations (birth defects) in a developing fetus by exogenous factors acting in the womb; interference with normal embryonic development.

Teratogenicity: The capacity of a physical or chemical agent to cause teratogenesis in offspring.

Terrace: A broad channel, bench, or embankment constructed across the slope to intercept runoff and detain or channel it to protected outlets, thereby reducing erosion from agricultural areas.

Tertiary Treatment: The third stage of treatment that brings water to a high degree of refinement or conditioning following the reduction of substances in the primary and secondary stages of treatment.

Therapeutic Index: The ratio of the dose required to produce toxic or lethal effect to dose required to produce nonadverse or therapeutic response.

Thermal Conductivity: The ability of a substance to conduct heat. Mathematically, the ratio of the rate of heat flow to the rate of temperature change in the particular substance.

Thermal Ozone Destructor: A unit in an ozonation system that employs high temperature to destroy excess ozone.

Thermal Stratification: The formation of layers of different temperatures in a lake or reservoir.

Thermocline: The layer in a lake which divides the warm upper current-mixed zone (epilimnion) from the colder lower deep-water stagnant zone (hypolimnion). During the warm summertime, the thermocline is the middle layer of the lake. Lying between the two layers, the thermocline loses heat rapidly. Also called the metalimnion.

Thermocouple: A heat-sensing device made of two conductors of different metals joined at their ends. An electric current is produced when there is a difference in temperature between the ends.

Thermoplastic: Materials such as certain synthetic resins and plastics that soften or fuse when heated and harden and become rigid when cooled, and that can usually be remelted and cooled time after time with no appreciable chemical change.

Thermoset: Certain plastics and synthetic resins that once solidified will not resoften or fuse when heated. Thermoset materials may decompose at high temperature, but will not soften or melt.

Thin-Film Composite Membrane: A class of reverse osmosis membranes made with polyamide-based polymer and fabricated with different materials in the separation and support layers.

Thiobacillus: A genus of bacteria that obtain their energy from oxidation of sulfides, thiosulfates, or sulfur, forming sulfur, persulfates, sulfuric acid, and sulfates.

Thiobacillus: A genus of bacteria that obtain their energy from oxidation of sulfides, thiosulfates, or sulfur, forming sulfur, persulfates, sulfuric acid, and sulfates.

Threshold: The lowest dose of a chemical at which a specified measurable effect is observed and below which it is not observed.

Threshold Odor: The minimum odor of a water sample that can just be detected after successive dilutions with odorless water. Also called odor threshold.

Threshold Odor Number: The greatest dilution of a sample with odor-free water that still yields a just-detectable odor.

Threshold Substance: See Trace Substance.

Throughput Volume: The amount in gallons or liters of water passed through an ion exchange resin bed or water treatment system before exhaustion of the exchanger or system is reached.

Thrust Block: A mass of concrete of similar material appropriately placed around a pipe to prevent movement when the pipe is carrying water. Usually placed at bends and valve structures.

Tillage: Plowing, seedbed preparation, and cultivation practices.

Time Lag: The time required for processes and control system to respond to a signal or to reach a desired level.

Time Weighted Average: The average value of a parameter (e.g., concentration of a chemical in air) that varies over time.

Timer: A device for automatically starting or stopping a machine or other device at a given time.

Tissue: A group of similar cells.

Titrate: To titrate a sample, a chemical solution of known strength is added on a drop-by-drop basis until a certain color change, precipitate, or pH change in the sample is observed (endpoint). Titration is the process of adding the chemical reagent in increments until completion of the reaction, as signaled by the endpoint.

Titration: An analytical technique for determining how much of a certain substance (concentration) is present in a solution (such as a water sample) by measuring how much of another substance (of known concentration) must be added to produce a given reaction (often color change in the solution). Titration is used for determining the level of concentration of a substance in solution. This procedure is widely used in water testing.

Too Numerous to Count: The total number of bacterial colonies exceeds 200 on a 47mm diameter membrane filter used for coliform detection.

Topography: The arrangement of hills and valleys in a geographic area.

Tortuous Path: Water flow through channels which are constricted and marked by repeated twists, bends and winding turns. In an electrodialysis system, water flow in which spacers, turbulence promoters or cross traps are used to produce turbulence in the flow stream.

Total Acidity: The total of all forms of acidity in a solution, including mineral acidity, carbon dioxide, and acid salts.

Total Alkalinity: See Alkalinity.

Total Capacity: See Rated Capacity.

Total Chlorine: The total concentration of the chlorine in a water, including the combined available chlorine and the free available chlorine.

Total Chlorine Residual: The total amount of chlorine residual present in a water sample, without regard to type.

Total Dissolved Phosphorus: Total phosphorus content of material that will pass through a filter of a specific size.

Total Dissolved Solids (TDS): The total weight of the solids that are dissolved in the water, give in ppm per unit volume of water. TDS is determined by filtering a given volume of water (usually through a 0.45 micron filter), evaporating it at a defined temperature (usually 103-105 degrees Celsius), and then weighing the residue. Note: A test measuring the electrical conductivity of the water provides only an estimate of the TDS present, as conductivity is not precisely proportional to the weight of an ion and nonconductive substances cannot be measured by electrical tests.

Total Dynamic Head (TDH): When a pump is lifting or pumping water, the vertical distance (in feet) from the elevation of the energy grade line on the suction side of the pump to the elevation of the energy grade line on the discharge side of the pump.

Total Hardness (TH): The total of the amounts of divalent metallic cations, principally calcium hardness and magnesium hardness, expressed in terms of calcium carbonate equivalent.

Total Matter: The sum of all suspended and dissolved matter in a water sample.

Total Nitrogen: The sum of all nitrogen forms.

Total Organic Carbon (TOC): The amount of carbon covalently bound in organic compounds in a water sample. TOC is measured by the amount of carbon dioxide produced when a water sample is atomized in a combustion chamber.

Total Ozone Demand: The total amount of ozone gas which must be mixed with a liquid (water), solid, or gas in order to satisfy all the ozone oxidation requirements.

Total Particulate Phosphorus: Total phosphorus content of material retained on a filter of a specific size.

Total Phosphorus: The sum of all phosphorus forms.

Total Residual Chlorine: The amount of available chlorine remaining after a given contact time. The sum of the combined available residual chlorine and the free available residual chlorine.

Total Solids (TS): The weight of all organic and inorganic solids, both dissolved and suspended, per unit volume of water. The weight of total solids in a solution is generally determined by evaporation of a measured volume of water at 105 degrees C in a preweighed dish.

Total Suspended Solids: The particles which can be removed from a solution by filtration, usually specified as the matter which will not pass through a 0.45 micron pore-diameter filter.

Total Trihalomethanes (TTHMs): The sum of the concentration, in milligrams per liter, of the trihalomethane compounds [trichloromethane (chloroform), dibromochloromethane, bromodichloromethane, and tribromomethane (bromoform)], rounded to two significant figures.

Totalizer: A device that tallies and indicates the total quantity of flow through a measuring device. Also called an integrator.

Toxaphene: A chemical that causes adverse health effects in domestic water supplies and also is toxic to freshwater and marine aquatic life.

Toxic: Poisonous (to living organisms); capable of producing disease or otherwise harmful to human health when taken into the body.

Toxic Substances: Chemical elements and compounds, such as lead, radon, benzene, dioxin, and numerous others, that have toxic properties by either ingestion, inhalation, or absorption into the human body. There is considerable variation in the degree of toxicity among the various toxic substances and in the exposure level that induces toxicity.

Toxicant: A harmful substance or agent that may injure an exposed organism.

Toxicity: The quality of being toxic.

Toxicity Assessment: Characterization of the toxicological properties and effects of a chemical, including all aspects of its absorption, metabolism, excretion, and mechanism of action, with special emphasis on establishment of dose-response characteristics.

Toxicology: The science and study of poisons control.

Trace Element: An element essential to plant and/or animal nutrition in trace concentration of one percent or less. For example, iron, manganese, zinc, copper, potassium, sodium, etc. Such elements are also called micronutrients.

Trace Substance (or Trace): A substance which is found during water analysis in a very small concentration high enough to be detected, but too low to be quantified accurately by standard testing methods. Sometimes referred to as a threshold substance.

Transducer: A device which senses some varying condition and converts it to an electrical signal for transmission to some other device (a receiver) for processing or decision-making.

Transformation: Acquisition by a cell of the property of uncontrolled growth.

Transient Water System: A noncommunity water system that does not serve 25 of the same nonresident persons per day for more than six months per year. Also called a transient noncommunity water system (TNCWS).

Transmission Lines: Pipelines that transport raw water from its source to a water treatment plant. After treatment, water is usually pumped into pipelines (transmission lines) that are connected to a distribution grid system.

Transmission of Ultraviolet: The percentage of light wave length at 2537 angstrom units transmitted through water.

Transmissivity: The ability of an aquifer to transmit water

Transmittancy: The ability of water to transmit or convey ultraviolet energy.

Transpiration: The process by which water vapor is released to the atmosphere by living plants.

Treated Waste Water: Waste water that has been subjected to one or more physical, chemical, and biological processes to reduce its pollution of health hazard.

Tremie: A device used to place concrete or grout under water.

Trichloroethylene (TCE): A toxic volatile organic compound often used as a solvent.

Trigger Point: A stage in a demand initiated regeneration (DIR) water softener or valve control cycle when the unit is ready for regeneration.

Trihalomethanes (THMs): A group of organic chemicals, suspected of being carcinogenic, which are formed in water when chlorine being used as a disinfectant reacts with natural organic matter such as humic acids from decayed vegetation. Humic acids are present in all natural water used as sources of drinking water supplies. Chloroform is one of the most common THMs formed in this type of reaction.

Trivalent: Having a valence of three.

Trophic Status: The ability of a lake to support plant growth as measured by phosphorus content, algae abundance, and depth of light penetration.

Tube Settler: A device that uses bundles of small bore (2 to 3 inches or 50 to 75 mm) tubes installed on an incline as an aid to sedimentation. The tubes may come in a variety of shapes including circular and rectangular. As water rises within the tubes, settling solids fall to the tube surface. As the sludge (from the settled solids) in the tube gains weight, it moves down the tubes and settles to the bottom of the basin for removal by conventional sludge collection means. Tube settlers are sometimes installed in sedimentation basins and clarifiers to improve particle removal.

Tubercle: A protective crust of corrosion products (rust) which builds up over a pit caused by the loss of metal due to corrosion.

Tuberculation: The development or formation of small mounds of corrosion products (rust) on the inside of iron pipe. These mounds (tubercules) increase the roughness of the inside of the pipe, thus increasing resistance to water flow (decreases the C factor).

Tumor Incidence: Fraction of animals having a tumor of a certain type.

Turbid: Having a cloudy or muddy appearance.

Turbidimeter: A device that measures the amount of light scattered by suspended solids in a liquid.

Turbidity: The amount of small particles of solid matter suspended in water as measured by the amount of scattering and absorption of light rays caused by the particles. Turbidity blocks light rays and makes the water opaque. Turbidity is measured in nephelometric turbidity units (NTU). Potable water should not exceed 0.5 NTU. Turbidity cannot be directly equated to suspended solids because white particles reflect more light than dark-colored particles and many small particles will reflect more light than an equivalent large particle.

Turbulence: A pattern of water flow characterized by cross currents and eddies which mix the water (as opposed to a streamlined or laminar flow pattern). Turbulence may be caused by excessive flow rates, curves or rough surfaces in the flow channel, or by turbulence promoters (such as baffles) purposely created to mix the water. Turbulence significantly increases pressure drop in a system.

Turbulence Promoter: Devices which are inserted into the feedwater channel or the product water channel to increase the turbulence and improve the mixing characteristics of the fluid flow. Typical turbulence promoters include baffles, spiral wires, balls, spacers, and static kinetic-type mixers.

Turbulent Flow: See Turbulence.

Turnover: The mixing of the lower and upper layers of a lake, generally occurring in the spring and the fall, caused by temperature change and density equalization. Also called overturn.

Two-Bed: A pairing of cation and anion exchange tanks and typically operating in series. It is best used for the deionization of relatively high volumes of water and is capable of producing product water with resistivity of up to one megohm-centimeter.

Type 1 Resin: A strong base polystyrene/divinylbenzene anion exchange resin in which the exchange site is a trimethylamine [-N(CH₃)₃]. Type 1 resins are inherently more stable both chemically and thermally than type 2 resins, especially in the hydroxide form. They, therefore, typically have a longer life potential and can be regenerated at higher temperatures (e.g., for low silica effluents). However, type 1 resins have a lower affinity for hydroxide ion relative to other anions than does type 2 resin. It typically has lower operating capacity, lower regeneration efficiency, and lower organic fouling resistance than type 2 resin. Type 1 resins sometimes emit a very fishy odor.

Type 2 Resin: A strong base polystyrene/divinylbenzene anion exchange resin in which the exchange site is a dimethylethanol amine [-N(CH₃)₂(CH₂^–CH₂OH)], i.e., an alcohol takes the place of one of the methyl groups on the type 1 resin. The alcohol can sometimes be cleaved off the amine group during operations leaving a weak base exchange site on the type 2 resin and imparting a characteristic alcohol-like odor. Resins also typically require longer rinse times as they lose strong base capacity. The type 2 resin is not as stable as its type 1 counterpart, but because of its higher affinity for the hydroxide ion relative to other anions, it has a higher operating capacity, a higher regeneration efficiency, and is much more resistant to organic fouling.

USP: United States Pharmacopeia.

USP Grade Water: See Pharmaceutical Grade Water.

USTs: Underground Storage Tanks.

Ultrafiltration: A method of cross flow filtration (similar to reverse osmosis but using lower pressures) which uses a membrane to separate small colloids and large molecules from water and other liquids. The ultrafiltration process falls between reverse osmosis and microfiltration in terms of the size of particles removed, with ultrafiltration removing particles in the 0.002 to 0.1 micron range, and typically rejecting organics over 1,000 molecular weight while passing ions and smaller organics.

Ultrapure Water: Highly-treated water that is deionized and mineral-free with high resistivity and no organics; it is usually used in the semiconductor and pharmaceutical industries. Ultrapure water is NOT considered biologically pure (potable) or sterile. There is no set numerical standard to determine exactly what “ultrapure” water is or should be.

Ultraviolet (UV): Pertaining to ultraviolet light.

Ultraviolet (UV) Light: Radiation (light) having a wavelength shorter than 3900 angstroms, the wavelengths of visible light, and longer than 100 angstroms, the wavelengths of x-rays. This wavelength puts ultraviolet light at the invisible violet end of the light spectrum. Ultraviolet light is used as a disinfectant.

Ultraviolet (UV) Light Spectroscopy: See Spectroscopy

Ultraviolet Absorber: Substances which absorb ultraviolet radiation (light). Ultraviolet absorbers are added to plastic (such as used in plastic tanks and fittings) and rubber products to make them less likely to decay as the result of absorbing ultraviolet rays.

Ultraviolet Chamber: The area where the water is irradiated with ultraviolet rays.

Ultraviolet Demand: The amount of ultraviolet rays required to inactivate certain microorganisms.

Ultraviolet Dosage: The amount of disinfectant ultraviolet rays delivered to the organisms in the water being disinfected. Dosage is a combination of UV intensity times the contact time and is measured in watt-seconds per square centimeter.

Unaccounted-for Water: A term used by public and municipal water systems to describe the difference between the amount of finished water produced and the amount registered on meters as sold. Unaccounted-for water may range from 10 percent-35 percent of finished water produced by the utility and usually includes water lost from leaky water mains, water lost in firefighting or from fire hydrants, or other public or municipal uses.

Uncertainty Factor: A number (equal to or greater than one) used to divide the NOAEL or LOAEL value derived from measurements in animals or small groups of humans, in order to estimate a NOAEL value for the whole human population.

Unconfined Aquifer: An aquifer containing water that is not under pressure; the water level in a well is the same as the water table outside the well.

Underbed: A layer of gravel or grout used to fill the bottom curved base of a larger filter or softener tank, usually in a system with a header-lateral design. Underbed is not necessarily the same as the media support bed.

Underdrain: The drainage piping arrangement to collect treated water at the bottom of the ion exchange or filter media beds.

Uniform Flow: A flow in which the feet per second velocity rates and directions are the same from point to point along the conduit.

Uniform Particle Size: The particle size distribution screen sizing for exchanger and filtration media as established by U.S. Mesh Standards.

Uniformity Coefficient: The measure of the variation in particle sizes of filter and ion exchange media. The uniformity coefficient is defined as the ratio of the sieve size that will permit passage of 60 percent of the media material by weight to the sieve size that will permit passage of 10 percent of the media material by weight. A uniformity coefficient of 1.00 denotes a material having particle grains all the same size; numbers increasingly greater than one denote increasingly less uniformity.

Unit Cancer Risk: Estimate of the lifetime risk caused by each unit of exposure in the low exposure region.

Unit Hydrograph: The hydrograph of one inch of storm runoff generated by a rainstorm of fairly uniform intensity within a specific period of time.

United States Pharmacopeia (USP): The official publication for drug product standards including six water quality standards for pharmaceutical uses. The USP was established by the U.S. Congress in 1884 to control makeup of drugs.

Univalent: Having a valence of one. Also called monovalent.

Unsaturated Zone: The area between the land surface and water table in which the pore spaces are only partially filled with water. Also called zone of aeration.

Unslaked Lime: See Lime

Upflow: A pattern of water flow in which a solution (water or regenerant usually) enters at the bottom of the vessel or column and flows out at the top of the vessel or column during any phase of the treatment unit’s operating cycle. The term is used to describe ion exchange system flow patterns or water flow through filter media. A system can have upflow during the treatment cycle and downflow during regeneration. Upflow is also called counter current flow. Countercurrent flow means regeneration flows and service flows are in the opposite directions.

Upflow Brining: Is a means of forcing the brine solution upward through the cation exchanger for regenerating the resin. Where the softening flow is downward and the regenerating brine flow is upward, the mode is also called countercurrent flow. Countercurrent flow means regeneration flows and service flows are in the opposite directions.

Upflow Softening: A pattern of water flow used in softeners in which the service water flows upward through the ion exchange bed; the media is restricted in movement, usually because of a packed bed. The regeneration brine usually flows downward in such systems. Upflow softening is normally used to achieve higher operating efficiency.

Upper Bound Estimate: Estimate not likely to be lower than the true risk.

Upper Distributor: The piping arrangement inside and at the top of softeners and filters to more uniformly distribute the incoming water over the resin or filter media bed. In small domestic units, this distributor also distributes the brine for regeneration.

Uranium (U): A radioactive metallic element found naturally only in combination with other substances. Uranium 238 (U-238) is the most common form, but about 0.7 percent of natural uranium is present as U-235, which is the important fissionable component in work with atomic energy. Uranium in natural water exists as anionic complexes UO₂(CO₃)₂^2- and UO₂(CO₃)₃^4-.

Urban Runoff: Stormwater from city streets and adjacent domestic or commercial properties that may carry pollutants of various kinds into the sewer systems and/or receiving waters.

User: The product water consumer.

User Fee: A fee which is collected only from those persons who use a particular service, as opposed to one collected from the public in general. User fees generally vary in proportion to the degree of use of the service.

Vacuum Breaker: A mechanical device which automatically vents a water line to the atmosphere when subject to a partial vacuum, thus preventing back siphonage.

Vacuum Distillation: Distillation that occurs at a pressure somewhat below atmospheric pressure. Lowering the pressure also lowers the boiling point of water, thus conserving energy by requiring less heat to bring about distillation.

Vacuum Filtration: The filtration process in which a partial vacuum is applied to increase the rate of filtration by causing the water to be sucked through the filter medium. This is one of the oldest mechanical dewatering techniques in continuous use. In municipal softening, this process is used to separate water from the lime sludge for sludge disposal.

Vacuum Freezing: A form of desalination using a vacuum to help cool and fast freeze high TDS source water which separates the solids by concentrating them in the portion of the water that doesn’t freeze, or that freezes last in a similar manner to what occurs in the cloudy centers of ice cubes.

Vacuum Pan: An airtight container used to produce granulated water softener salt using a process involving the evaporation of brine-turned-to-steam in a partial vacuum.

Vacuum Pump: A pumping apparatus which exhausts gas or air from an enclosed space to achieve a desired degree of vacuum.

Valence: A whole number (positive or negative) representing the power of one element to combine with another. In general terms, the valence number represents the number of electrons in an atom or combined group of atoms which can be easily given up or accepted to react with or bond to another atom or group of atoms to form a molecule.

Validation: 1. (water treatment industry) Determination upon testing that a representative sample of a water treatment equipment model has met the requirements of a specified standard.
2. (pharmaceutical industry) The requirement of certain quality control testing and record keeping procedures to ensure compliance not only with a specific quality but also with a specific means to achieve and ensure that quality.

Van der Waals Forces: Weak attractive forces acting between molecules. These forces are somewhat weaker than hydrogen bonds and far weaker than interatomic valences.

Vapor: The gaseous form of any substance whose usual form is a liquid or a solid. Visible particles of moisture suspended in air, such as mist or fog.

Vapor Pressure: The pressure, often expressed in millimeters of mercury (mm Hg), at which a vapor is in a state of balance with its liquid or solid form.

Variable Costs: Input costs that change as the nature of the production activity of its circumstances change; for example, as production levels vary.

Variance: A State with primary enforcement responsibility under the Safe Drinking Water Act may relieve a public water system from a requirement respecting an MCL by granting a variance if certain conditions exist. These are:
1. The system cannot meet the MCL in spite of the application of best available treatment technology, treatment techniques, or other means (taking costs into consideration), due to the characteristics of the raw water sources which are reasonably available to the system; and the variance will not result in an unreasonable public health risk.
2. A system may also be granted a variance from a specified treatment technique if it can show that, due to the nature of the system’s raw water source, such treatment is not necessary to public health.

Vegetative Controls: Nonpoint source pollution control practices that involve plants (vegetative cover) to reduce erosion and minimize the loss of pollutants.

Velocity: As relates to general water treatment, the time measurement of linear motion (flow) in a given direction. For example, water flowing 60 feet in a conduit each minute has a velocity of 60 feet per minute (fpm) or one foot per second (1 fps).

Velocity Head: See Head

Velocity Profile: The relationship between the velocity of fluid flowing adjacent to the conduit wall or membrane surface and that flowing at a distance from the wall or surface.

Venturi: A tube with a narrow throat (a constriction) that increases the velocity and decreases the pressure of the liquid passing through it, creating a partial vacuum immediately after the constriction in the tube. The vacuum created has a sucking effect (eduction), and a venturi is commonly used to introduce a liquid (such as a regenerant) or gas (such as air) into a flowing water stream.

Versenate: A chemical substance used in water analysis for water hardness or with an indicator to colorimetrically measure hardness quality.

Viable: 1. Capable of living independently (as in a fetus capable of living outside the womb) and being reproductive (as microorganisms capable of colonizing and thriving).
2.Workable (as a viable idea).

Viable Treatment Process: A water or waste water treatment process capable of accomplishing the desired water quality.

Virulence: Degree of ability to cause disease.

Virus: A parasitic infectious microbe, composed almost entirely of protein and nucleic acids, which can cause disease(s) in humans. Viruses can reproduce only within living cells. They are 0.004 to 0.1 microns in size, and about 100 times smaller than bacteria.

Viscosity: The tendency of a fluid to resist flowing due to internal forces such as the attraction of the molecules for each other (cohesion) or the friction of the molecules during flow. Viscosity varies with water temperature.

Vitriol: See Sulfuric Acid

Void Volume: The volume occupied by the interstitial spaces between the particles of ion exchangers, filter media, or other granular materials in a bed or column. Often expressed as percent of the total volume occupied by the medium bed.

Volatile: Capable of becoming vapor at relatively low temperatures.

Volatile Acids: Acids produced during digestion. Fatty acids which are soluble in water and can be steam-distilled at atmospheric pressure. Also called organic acids. Volatile acids are commonly reported as equivalent to acetic acid.

Volatile Liquids: Liquids which easily vaporize or evaporate at room temperatures.

Volatile Organic Chemicals (VOCs): Organic chemicals that turn into vapor at relatively low temperatures.

Volatile Solids: The term used in the laboratory analysis of the solids content of a substance (such as water) to define the portion of the total suspended and/or dissolved solids that become expulsed or driven off after heating or burning a given sample of the substance at a specified temperature and for a specified time.

Volatilization: Loss of a substance through evaporation.

Voltage: The electrical pressure available to cause a flow of current (amperage) when an electrical circuit is closed.

Volumetric: A measurement based on the volume of some factor. Volumetric titration is a means of measuring unknown concentrations of water quality indicators in a sample by determining the volume of titrant or liquid reagent needed to complete particular reactions.

Vortex: A revolving mass of water which forms a whirlpool. This whirlpool is caused by water flowing out of a small opening in the bottom of a basin or reservoir. A funnel-shaped opening is created downward from the water surface.

WFI: Water For Injection.

WHO: World Health Organization.

Waste Water: Water that has been used.
1. (RO, ultrafiltration, electrodialysis) The stream of water (not product water) created as the result of processing water–the reject water or concentrate.
2. (ion exchange and filtration) The spent water used in the total backwash/and or regeneration cycle.
3. The used water and solids from a residence or a community (including used water from industrial processes) that flow to a septic system or a treatment plant.   Storm water, surface water, and groundwater infiltration also may be included in the waste water that enters a waste water treatment plant. The term sewage usually refers to household wastes, but this word is being replaced by the term waste water.

Waste Water Treatment Plant: A facility that receives waste waters (and sometimes runoff) from domestic and/or industrial sources, and by a combination of physical, chemical, and biological processes reduces (treats) the waste waters to less harmful byproducts; known by the acronyms WWTP, STP (sewage treatment plant), and POTW (publicly owned treatment works).

Water: [H₂O] An odorless, colorless, tasteless liquid which exists as ice in solid form (phase) and steam in vapor form (phase). It freezes at 32 degrees F (0 degrees C) and boils at 212 degrees F (100 degrees C). Water is a polar liquid with high dielectric constant which accounts for its solvent power; it is called the universal solvent. It is a weak electrolyte; in pure water, only about two molecules in every 1,100,000,000 separate into H₃O⁺ and OH^–ions. Water is only slightly compressible. It is the liquid that descends from the clouds as rain and forms lakes, streams, and seas (oceans). Water is a major constituent of all living matter. Also referred to as H₂O (dihydrogen oxide) and HOH (hydrogen hydroxide).

Water Bloom: A prolific growth of plankton, including blue-green algae, which may occur and be so dense that it imparts a greenish, yellowish, or brownish color to water near the surface of a lake, pond, or reservoir.

Water Budget: A summation of inputs, outputs, and net changes to a particular water resource system over a fixed period. Also, water balance model.

Water Closet: A flushable toilet.

Water Conditioner: SEE water treatment device

Water Conditioning: SEE water treatment.

Water Cycle: SEE Hydrologic Cycle

Water Density (maximum): The maximum density of water is reached at 39 degrees Fahrenheit (4 degrees Centigrade). It becomes less dense at both higher and lower temperatures.

Water Flooding: A process in underground mining such as oil recovery in which oil or a mineral from underground formations is replaced by an infusion of warm, softened water thus bringing the underground substance to the surface for recovery. Also known as oil well flooding.

Water Flux: SEE Flux

Water Glass: The common name of a sodium silicate (Na₂O x SiO₂) substance used for corrosion control in potable waters. It is also an ingredient used in the manufacture of synthetic gel zeolite. SEE ALSO silica. It is also an ingredient used in the manufacture of synthetic gel zeolite.

Water Hammer: The shock wave or series of waves caused by the resistance of inertia to an abrupt change (acceleration or deceleration) of water flow through a water piping system. Water hammer may produce an instantaneous pressure many times greater than the normal pressure. For this reason, many building codes now require the installation of a “water hammer arrestor,” a device to absorb these shock waves and prevent damage to appliances such as washing machines.

Water Head: SEE Head

Water Jacket: An outer casing which holds water or through which water flows and circulates to absorb heat and cool the interior of the mechanism or machinery that the water jacket is surrounding.

Water Processing: SEE Water Conditioning

Water Purveyor: An agency or person that supplies water (usually potable water).

Water Regain: SEE Water Retention

Water Retention: The amount of water, expressed as a percent of the wet weight of an ion exchanger, retained within the resin bead and on the surface of fully swollen and drained ion exchange media. Also called water regain.

Water Softener: A device, product, or equipment that reduces the presence of water hardness to less than 1 gpg expressed as calcium carbonate (CaCO₃) equivalent via chemical, physical, or other means. In residential and commercial applications, the most common water softener consists of a pressurized water treatment device in which hard water is passed through a bed of cation exchange media (either inorganic or synthetic organic) for the purpose of exchanging calcium and magnesium ions for sodium or potassium ions, thus producing a softened water which is more desirable for laundering, bathing, and dishwashing. This cation exchange process was originally called zeolite softening or the Permutit Process. Most modern water softeners use a sulfonated bead form of styrene/divinylbenzene (DVB) cation resin. Distillation, electrodialysis, nanofiltration, deionization, and reverse osmosis water treatment systems are also capable of measurably removing calcium and magnesium ions from water and therefore act as water softeners. SEE ALSO no-salt water softener; physical water treatment device.

Water Softener Salt: Salt suitable for regenerating residential and commercial cation exchange water softeners. Most commonly used for this purpose is sodium chloride (NaCl) in crystal or pelletized form. Rock grade salt should be 96-99 percent NaCl; evaporated salt should be 99+ percent NaCl. Potassium chloride (KCl) may also be used for the regeneration cycle in the cation exchange process, thus minimizing the amount of sodium added to both the softened water and the spent regenerant water going to the drain.

Water Softening: A water treatment process for hard water whereby the concentration of hardness minerals is decreased. The process, itself, does not necessarily produce soft water or softened water. SEE ALSO ion exchange; lime and soda ash softening; lime softening; water softener.

Water Solubility: The maximum concentration of a chemical compound which can result when it is dissolved in water. If a substance is water soluble, it can very readily disperse through the environment.

Water Source: The basic origin of a water, either a surface source (such as a lake, river, or reservoir) or a subsurface source (such as a well). After treatment and pumping via pipe lines, the treated and pumped water becomes a water supply.

Water Spotting: Cloudy milk-like film, spots, streaks, or heavy white deposits left on surfaces after water has dried from them, especially noticeable on clear glassware and cars after washing. Spotting is caused by minerals that had been dissolved in the water remaining behind after the water has evaporated away. Soft water spotting can be wiped off easily with a damp cloth or rinsed off with a little fresh water. Hard water deposits, on the other hand, are comprised of the more tenacious calcium and magnesium salts. Hard water films typically require harsh abrasives or an acid cleaner to remove them. A third type of water residue film is due to silica (SiO₂) deposits. Silica spotting is rare, but it is more difficult or impractical to be removed when it does occur. If glassware films won’t dissolve in acids such as vinegar or lemon juice, they may be due to silica spotting or etching. If the spot won’t dissolve in acid, but can be scratched off with a razor blade or pinpoint, it’s likely a silica film.

Water Spotting: Cloudy milk-like film, spots, streaks, or heavy white deposits left on surfaces after water has dried from them, especially noticeable on clear glassware and cars after washing. Spotting is caused by minerals that had been dissolved in the water remaining behind after the water has evaporated away. Soft water spotting can be wiped off easily with a damp cloth or rinsed off with a little fresh water. Hard water deposits, on the other hand, are comprised of the more tenacious calcium and magnesium salts. Hard water films typically require harsh abrasives or an acid cleaner to remove them. A third type of water residue film is due to silica (SiO₂) deposits. Silica spotting is rare, but it is more difficult or impractical to be removed when it does occur. If glassware films won’t dissolve in acids such as vinegar or lemon juice, they may be due to silica spotting or etching. If the spot won’t dissolve in acid, but can be scratched off with a razor blade or pinpoint, it’s likely a silica film.

Water Storage Pond: An impound for liquid wastes, so designated as to accomplish some degree of biochemical treatment of the wastes.

Water Supplier: A person who owns or operates a public water system.

Water Supply: SEE Water Source

Water Supply System: The collection, treatment, storage, and distribution of potable water from source to consumer.

Water Table: The level of groundwater. The upper surface of the zone of saturation of groundwater above an impermeable layer of soil or rock (through which water cannot move) as in an unconfined aquifer. This level can be very near the surface of the ground or far below it.

Water Treatment: Any method of purposefully changing the quality of water between its source and point of use.

Water Treatment Device: Any point-of-use or point-of-entry device that changes the quality of the water supply by any means, including, but not limited to, filtration, distillation, adsorption, ion exchange, reverse osmosis, or other treatment.

Water Treatment Lagoon: An impound for liquid wastes, so designed as to accomplish some degree of biochemical treatment of the wastes.

Water Well: An excavation where the intended use is for the location, acquisition, development, or artificial recharge of groundwater (excluding sandpoint wells).

Water of Hydration: Water which has been chemically combined with a substance to form a hydrate and which can then be removed (as by heating) without essentially changing the chemical composition of the substance.

Waterborne Disease: A disease, caused by a bacterium or organism able to live in water, which can be transmitted by water.

Waterborne Disease Outbreak: The significant occurrence of acute infectious illness, epidemiologically associated with the ingestion of water from a public water system that is deficient in treatment, as determined by the appropriate local or state agency.

Waterless Hand Cleaner: A paste, gel, or lotion that does not require rinsing. Waterless hand cleaners are useful when facilities for hand washing are not available and are also helpful in removing difficult soils. Available for use from dispensers, or directly from their own containers, they are usually oil-in-water emulsions. They are available with or without scrubbers. The scrubbers may be organic, (e.g., particles of polyethylene or polystyrene) or inorganic (pumice).

Waterlogged Tank: A tank (as in a domestic water well pumping system) in which too much water has accumulated and has replaced some of the air in the tank’s air cushion causing a disruption in the normal pressure pattern needed for pumping and uniform water flow.

Watershed: The land area that drains into a stream. An area of land that contributes runoff to one specific delivery point; large watersheds may be composed of several smaller “subsheds,” each of which contributes runoff to different locations that ultimately combine at a common delivery point.

Watertight: A condition existing in water treatment equipment and materials of such precision of construction and fit as to be impermeable to water unless sufficient pressure occurs to cause rupture.

Watt: A unit of power equal to one joule per second. The power of a current of one ampere flowing across a potential difference of one volt.

Weak Acid Cation Exchangers: Those cation exchange products with functional groups which, in the hydrogen form, are not capable of splitting neutral salts to form their corresponding free acids. Weak acid cation exchange resins have a much higher (three to four times higher) regeneration efficiency than their strong acid counterparts, but in the hydrogen form can only exchange cations that are associated with alkalinity. The cations associated with sulfates, chlorides, and nitrates, for example, cannot be removed with weak acid cation exchanger in the hydrogen form. Hydrogen form weak acid cation exchangers that have been neutralized with sodium hydroxide to the sodium form, however, can effectively remove both carbonate and noncarbonate water hardness cations; thus weak acid cation resins can be used to soften waters that, because of high total dissolved solids, are not possible or practical to treat with strong acid cation resins.

Weak Base Anion Exchangers: Those anion exchange products with functional groups which are not capable of splitting neutral salts to form corresponding free bases. Weak base anion exchange resins have a much higher (three to four times higher) regeneration efficiency than their strong base counterparts, but can only exchange mineral acid anions such as sulfate, chloride, and nitrate. The anions associated with weak acids, such as carbonates, bicarbonates, silicates, and organic acids, for example, cannot be removed with weak base anion exchange.

Weight Concentration Ratio: In ultrafiltration applications, the ratio of the initial weight of the feedwater to the weight of the reject water remaining at any time during the ultrafiltration process.

Weir: 1. A dam-like wall or plate placed in an open channel and used to measure the flow of water. The depth of the flow over the weir can be used to calculate the flow rate, or a chart or conversion table may be used.
2. A wall or obstruction used to control flow (from settling tanks and clarifiers) to assure uniform flow rate and avoid short-circuiting.

Weir Diameter: Many circular clarifiers have a circular weir within the outside edge of the clarifier. All the water leaving the clarifier flows over this weir. The diameter of the weir is the length of a line from one edge of a weir to the opposite edge and passing through the center of the circle formed by the weir.

Weir Loading: A guideline used to determine the length of weir needed on settling tanks and clarifiers in treatment plants. Used by operators to determine if weirs are hydraulically (flow) overloaded.

Well: A bored, drilled, or driven shaft, or a dug hole, whose depth is greater than the largest surface dimension and whose purpose is to reach underground water supplies or oil, or to store or bury fluids below ground.

Well Field: Area containing one or more wells that produces usable amounts of water.

Well Head: A particular well site location, as differentiated from other well site locations, that exist in the same water system.

Well Monitoring: The measurement, by on-site instruments or laboratory methods, of the quality of water in a well.

Well Plug: A watertight and gastight seal installed in a bore hole or well to prevent movement of fluids.

Wet Chemistry: Laboratory procedures used to analyze a sample of water using liquid chemical solutions (wet) instead of, or in addition to, laboratory instruments.

Wet-Salt Saturator Tank: A type of brine tank, so named because the saturated brine is always above the undissolved salt level, used on large commercial water softeners and older manual residential softeners. Most automatic home-sized water softeners now use dry-salt saturator tanks.

Wetlands: Any number of tidal and nontidal areas characterized by saturated or nearly saturated soils most of the year that form an interface between terrestrial (land-based) and aquatic environments; include freshwater marshes around ponds and channels (rivers and streams), brackish and salt marshes; other common names include swamps and bogs.

Wetting Agent: A compound that increases the ability and speed with which a liquid displaces air from a solid surface, thus improving the process of wetting that surface. Wetting agents are all surfactants. They function by lowering surface and interfacial tension. Soap and detergent surfactants serve as wetting agents in washing products, in addition to their other functions. In automatic dishwashing, nonionic surfactants are sometimes introduced into the last rinse for the purpose of maximizing drainage of water from dishes and utensils.

Whole-House Treatment: SEE Point-of-Entry (POE) Treatment

Wire-to-Water Efficiency: The efficiency of a pump and motor together. Also called the overall efficiency.

Withdrawal: The process of taking water from a source and conveying it to a place for a particular type of use.

Working Pressure: SEE Operating Pressure

World Health Organization (WHO): A part of the United Nations. The WHO, which is headquartered in Geneva, Switzerland, has compiled recommended standards for drinking water.

X -Rays: 1. Electromagnetic radiation with a very short wavelength (0.01 to 12 nanometers), shorter than ultraviolet radiation.
2. An image created by short-term exposure of an object to x-rays used in spectrometry analysis and medical therapy.

X-linked (Ion Exchange): See Cross-linking.

XPLE or PEX: Polyethylene that, by cross-linking via irradiation of linear polyethylene with an electron beam or gamma radiation, or with a chemical cross-linking agent, such as benzoly peroxide, is made to be a non-toxic thermosetting (remains solid upon heating) white solid with superior strength and durability, high temperature and pressure resistance, and inertness toward chemical attack and corrosion. Cross-linked polyethylene pipe and tubing is accepted by many plumbing codes for potable water distribution within buildings. It is flexible (bend radii of six times or greater the outside pipe/tubing diameter) and can be used in place of polybutylene (PB) water pipe.

Yield: The amount of product water produced by a water treatment process. The quantity of water (expressed as a rate of flow GPM, GPH, GPD, or total quantity per year) that can be collected for a given use from surface or groundwater sources. The yield may vary with the use proposed, with the plan of development, and also with economic considerations.

Zeolite Softening: A term formerly used for the removal of calcium and magnesium hardness from water by base exchange using natural or synthetic zeolites. Since the introduction of synthetic organic cation exchange resins, the more correct term is cation exchange softening. Zeolite softening was also called base exchange.

Zeolites: Hydrated sodium alumina silicates, either naturally-occurring mined products or synthetic products, with ion exchange properties. Zeolites were formerly used extensively for residential and commercial water softening but have been largely replaced by synthetic organic cation resin ion exchangers of polystyrene divinylbenzene substrate. Modified zeolites such as manganese greensand and synthetic manganese zeolites are still used as catalyst/oxidizing filters for the removal of iron, hydrogen sulfide, and manganese.

Zero Discharge Water: A discharge limit applied to manufacturing and commercial establishments in which only normal human sanitary waste waters may be discharged to the municipal sewerage system. All other types of waste water, such as that water used in manufacturing processes, are not included in zero discharge water; but they must be recycled, and the resulting waste product from such water must be taken to an alternate and approved disposal facility.

Zero Soft Water: A colloquial term for soft water that implies zero hardness. A field test to determine water hardness uses an indicator, that when mixed with hard water, turns pink. The solution is then titrated back with a chelator until it turns blue. Each drop of titrating solution counts as one grain (1 gpg). If the sample turns blue without the addition of any drops (zero drops), it is termed to be “zero” soft. However, it can range from 0 to <17.1 ppm. SEE ALSO soft water; hardness.

Zeta Potential: The electrical potential which exists across the interface of all solids and liquids. The potential represents the difference in voltage between the surface of the diffuse layer surrounding a colloidal particle and the bulk liquid beyond. Also known as electrokinetic potential.

Zone of Aeration: The comparatively dry soil or rock located between the ground surface and the top of the water table.

Zone of Saturation: The layer in the ground in which all available interstitial voids (cracks, crevices, holes) are filled with water. The level of the top of this zone is the water table.

Zooplankton: Small, usually microscopic animals (such as protozoans), found in lakes and reservoirs.