Water Glossary

	ABS	See Alkyl Benzene Sulfonate

	Absorbent	A material, usually a porous solid, which takes another material into its interior. When rain soaks into soil, the soil is an absorbent.

	Absorption	The process in which one substance is taken into the body of an absorbent.

	Acid	A substance which increases the concentration of 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.

	Acidity	The quantitative capacity of water or a water solution to neutralize an alkali or base. It is usually measured by titration with a standard solution of sodium hydroxide and expressed in terms of its calcium carbonate equivalent. (See mineral acidity, total acidity, carbon dioxide.)

	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 (1,233 cubic meters) or 325,851 gallons (1,233,L).

	Action Level	The level of lead or copper which, if exceeded, triggers treatment or other requirements that a water system must follow.

	Activated Carbon	A granular material usually produced by roasting various grades of coal in the absence of air. It has a very porous structure and it is used in water conditioning as an adsorbent (see "adsorption") for organic matter and certain dissolved gases. Sometimes called "activated charcoal".

	Activated Silica	A material usually formed from the reaction of a dilute silicate solution with a dilute acid. It is used as a coagulant aid.

	Acute Health Effect	An immediate (i.e. within hours or days) effect that may result from exposure to certain drinking water contaminants (e.g., pathogens).

	Adsorbent	A material, usually solid, capable of holding gases, liquids and/or suspended matter at its surface and in exposed pores. Activated carbon is a common adsorbent used in water treatment.

	Adsorption	The process in which matter adheres to the surface of an adsorbent.

	Aeration	The process in which air is brought into intimate contact with water, often by spraying water through air, or by bubbling air through water. Aeration may be used to add oxygen to the water for the oxidation of matter such as iron, or to cause the release of dissolved gases such as carbon dioxide or hydrogen sulfide from the water.

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

	Air Gap	A clear vertical space between a water or drain line and the flood level of a receptacle to prevent back-flow or siphoning from the receptacle in the event of negative pressure or vacuum. Most plumbing codes require the air gap to be at least twice the diameter of the water or drain line, with a minimum of 1-1/2 inches (3.8 cm). (See vacuum breaker or back-flow presenter.)

	Algae	Small primitive plants containing chlorophyll, commonly found in surface water. Excessive growths may create taste and odor problems, and consume dissolved oxygen during decay.

	Alkali	A group of water soluble mineral compounds, usually considered to have moderate strengths as bases (as opposed to the caustic or strongly basic hydroxides, although this differentiation is not always made). In general, the term is applied to bicarbonate and carbonate compounds when they are present in the water or solution. (See alkali, base.)

	Alkalinity	The quantitative capacity of a water or water solution to neutralize an acid. It is usually measured by titration with a standard acid solution of sulfuric acid and is expressed in terms of its calcium carbonate equivalent. (See alkali, base.)

	Alkyl Benzene Sulfonate	A term applied to a family of branched chain chemical compounds, formerly used as detergents,. Sometimes called "hard" detergents, because of their resistance to biological degradation, these compounds have been largely replaced with linear alkyl sulfonate (LAS) which are more readily degraded to simpler substances. (See detergent, linear alkyl sulfonate.)

	Alum	A common name for aluminum sulfate, used as a coagulant.

	Amoeba	A small, single-celled animal or protozoan.

	Anaerobic	An action or process conducted in the absence of air, such as the anaerobic digestion of organic matter by bacteria in a septic tank.

	Angstrom Unit	A unit of length equal to one ten-billionth of a meter.

	Anion	A negatively charged ion in solution, such as bicarbonate, chloride, nitrate or sulfate.

	Anion Exchange	An ion exchange process in which anions in solution are exchanged for other anions from an ion exchanger. In demineralization, for example, bicarbonate, chloride and sulfate anions are removed from solution in exchange for a chemically equivalent number of hydroxide anions from the anion exchange resin. (See ion exchange, demineralization.)

	Anode	The positive pole of an electrolytic system meter when oxidation occurs. Anodes made of magnesium 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.

	Aquifer	A natural underground layer, often of sand or gravel, that contains water.

	Arsenic	A natural element of the earth's crust, arsenic enters water supplies either through natural deposition or agricultural and industrial pollution. According to the Environmental Protection Agency (EPA), Office of Ground Water and Drinking Water, health effects of arsenic include skin damage, circulatory system problems and an increased risk of various cancers.

	Asbestos	A fibrous mineral, asbestos can enter water naturally or through the decay of asbestos cement in water mains. According to the Environmental Protection Agency (EPA), Office of Ground Water and Drinking Water, this contaminant may increase the risk of developing benign intestinal polyps and has been linked to cancer.

	Atom	The smallest particle of an element that can exist either alone or in combination.

	Atrazine	Atrazine is an herbicide contaminant which has been in the news lately after, being upgrade from a "possible" to a "likely" carcinogen. according to USA Today, atrazine is the most commonly used herbicide. Atrazine enters water supplies as runoff from farmers' fields. According to the EPA, atrazine causes cardiovascular system problems and reproductive difficulties.

	Attrition	In water treatment, the process in which solids are worn down or ground down by friction, often between particles of the same material. Filter media and ion exchange materials are subject to attrition during backwashing, regeneration and service.

	Back-Flow	Flow of water in a pipe or line in a direction opposite to normal flow. Often associated with back siphonage or the flow of possibly contaminated water into a potable water system.

	Back-Flow Preventer	A device or system installed in a water line to stop back-flow. (See vacuum breaker, air gap.)

	Backwash	The process in which beds of filter or ion exchange media are subjected to flow opposite to the service flow direction to loosen the bed and to flush suspended matter collected during the service run.

	Bacteria	Unicellular prokaryotic microorganisms which typically reproduce by cell division.

	Base	A substance which releases hydroxyl ions when dissolved in water. Bases react with acids to form a neutral salt and water. (See alkali.)

	Base Exchange	Synonymous with cation exchange.

	Batch	A quantity of material treated or produced as a unit.

	Batch Operation	A process method in which a quantity of material is processed or treated usually with a single charge of reactant in a single vessel, and often involving stirring. Example: The neutralization of a specific volume of an acid with a base in a vessel, with stirring or mixing, is a batch operation.

	Bed	The ion exchanger or filter media in a column or other tank or operational vessel.

	Bed Depth	The height of the ion exchanger or filter media in the vessel after preparation for service.

	Bed Expansion	The increase in the volume of a bed of ion exchange or filter media during upflow operations, such as backwashing, caused by lifting and separation of the media. Usually expressed as the percent of increase of bed depth.

	Best Available Technology	The water treatment(s) that EPA certifies to be the most effective for removing a contaminant.

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

	Biochemical Oxygen Demand (Bod)	The amount of oxygen consumed in the oxidation of organic matter by biological action under specific standard test conditions. Widely used as a measure of the strength of sewage and waste water.

	Biodegradable	Subject to degradation to simpler substances by biological action, such as the bacterial breakdown of detergents, sewage wastes and other organic matter.

	Bleach	An oxidizing agent formulated to break down colored matter. Includes the widely used hypochlorites, as well as perborates and other special purpose materials.

	Bod	Abbreviation for "Biochemical Oxygen Demand".

	Brackish Water	Water having salinity values ranging from approximately 500 to 5,000 parts per million (milligrams per liter).

	Breakpoint Chlorination	A chlorination procedure in which chlorine is added until the chlorine demand is satisfied and a dip (breakpoint) in the chlorine residual occurs. Further additions of chlorine produce a chlorine residual proportional to the amount added.

	Breakthrough	The appearance in the effluent from a water conditioner of the material being removed by the conditioner, such as hardness in the effluent of a softener, or turbidity in the effluent of a mechanical filter; an indication that regeneration, backwashing, or other treatment is necessary for further service.

	Brine	A strong solution of salt(s), such as sodium chloride used in the regeneration of ion exchange water softeners, but also applied to the mixed sodium, calcium and magnesium chloride waste solution from regeneration.

	Buffer	A chemical which causes a solution to resist changes in pH, or to shift the pH to a specific value.

	Builder	A chemical incorporated in a detergent formulation to produce a desired alkalinity level and improve the ability to suspend soil. The alkaline phosphates are widely used for this purpose.

	Bypass	A connection or a valve system that allows untreated water to flow through a water system while a water treatment unit is being regenerated, backwashed or serviced; also applied to a special water line installed to provide untreated water to a particular tap, such as a sill cock.

	Calcium	One of the principal elements in the earth's crust. When dissolved, in water, calcium is a factor contributing to the formation of scale and insoluble soap curds which are a means of clearly identifying hard water.

	Calcium Carbonate Equivalent	A common basis for expressing the concentration of hardness and other salts in chemically equivalent terms to simplify certain calculations; signifies that the concentration of a dissolved mineral is chemically equivalent to the stated concentration of calcium carbonate.

	Calcium Hypochlorite	A chemical compound, [Ca(Cl 0)24H2O], used as a bleach and as a source of chlorine in water treatment; specifically useful because it is stable as a dry powder and can be formed into tablets.

	Capacity	An expression of the quantity of an undesirable material which can be removed from water by a water conditioning medium, i.e., cleaning, regeneration or replacement, as determined under standard test conditions. For ion exchange water softeners, the capacity is expressed in grains of hardness removed between successive regenerations and is related to the pounds of salt used in regeneration. For filters, the capacity may be expressed in the length of time or total gallons delivered between servicing.

	Capacity Curve	A graph of the capacity versus regenerant levels for an ion exchange unit or system.

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

	Carbon Chloroform Extract	The matter adsorbed from a stream of water by activated carbon, and then extracted from the activated carbon with chloroform, using a specific standardized procedure; a measure of the organic matter in a water.

	Carbon Dioxide	A gas present in the atmosphere and formed by the decay of organic matter; the gas in carbonated beverages; in water it forms carbonic acid.

	Carbonaceous	Materials of or derived from organic substances such as coal, lignite, peat, etc.

	Carbonaceous Exchanger	Ion exchange material produced by the sulfonation of carbonaceous matter.

	Carbonate	The CO32 ion.

	Carbonate Alkalinity	Alkalinity due to the presence of the carbonate ion (CO32).

	Carbonate Hardness	Hardness due to the presence of calcium and magnesium bicarbonates and carbonates in water; the smaller of the total hardness and the total alkalinity. (See temporary hardness.)

	Carbonic Acid Formed	It does not contribute to total dissolved solids, but does have a pronounced effect on specific resistance. This effect must be included when estimating the water quality from a weak base deionizer. Carbonate and bicarbonate alkalinity are destroyed by cation resin and converted to carbonic acid. To calculate carbonic acid formed add the carbonates, bicarbonates, and twice the carbon dioxide.

	Carboxylic	An organic acidic group (COOH) which contributes cation exchange ability to some resins.

	Cartridge	Any removable preformed or prepackaged component containing a filtering media or ion exchanger.

	Cathode	The negative pole of an electrolytic system; an electrode where reduction occurs. (See anode.)

	Cathodic Protection	A corrosion control system in which the metal to be protected is made to serve as a cathode, either by the deliberate establishment of a galvanic cell or by impressed current. (See anode.)

	Cation	An ion with a positive electrical charge. Calcium, magnesium and sodium are cations.

	Cation Exchange	Ion exchange process in which cations in solution are exchanged for other cations from an ion exchanger.

	Cation Load Factory	This is the sum of calcium, magnesium, sodium, and potassium. It is the sum of all cations.

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

	Caustic Soda	The common name for sodium hydroxide.

	Cc	Abbreviation for "carbon chloroform extract".

	Channeling	The flow of water or other solution through a limited number of passages in a filter or ion exchanger bed, instead of distributed flow through all passages in the bed. May be due to fouling of the bed and plugging of many passages, poor distributor design, flow rates which are too low, faulty operational procedures, or other causes.

	Chelate	To form a complex chemical compound in which an ion, usually metallic, is bound into a stable ring structure.

	Chelating Agent	A chemical compound sometimes fed to water to tie up undesirable metal ions, keep them in solution, and eliminate or reduce the normal effects of the ion. (See sequestering agent.)

	Chemical Stability	Resistance to attach by chemical action.

	Chlorides	Salts of chloride are generally soluble. High concentrations contribute to corrosion problems.

	Chlorinator	A device designed to feed chlorine gas or solutions of its compounds, such as hypochlorite, into a water supply.

	Chlorine	A gas, C2, widely used in the disinfection of water and an oxidizing agent for organic matter, iron, etc.

	Chlorine Demand	A measure of the amount of chlorine consumed by oxidizable substances in a water before a chlorine residual will be found.

	Chronic Health Effect	The possible result of exposure over many years to a drinking water contaminant at levels above its MCL.

	Coagulant	A material, such as alum, which will 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 by forming larger or heavier particles, speeding the reactions, or by permitting reduced coagulant dosage.

	Coagulation	The process in which very small, finely divided solid particles are agglomerated into larger particles.

	Cod	The abbreviation for "Chemical Oxygen Demand".

	Coliform Bacteria	A group of microorganisms used as indicators of water contamination, and the possible presence of pathogenic (disease producing) bacteria.

	Coliform	A group of related bacteria whose presence in drinking water may indicate contamination by disease-causing microorganisms.

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

	Colloid	Very finely divided solid particles which do not settle out of a solution; intermediate between a true dissolved particle and a suspended solid which will settle out of solution. The removal of colloidal particles usually requires coagulation.

	Color	The shade or tint imparted to water by substances in true solution, and thus not removed by mechanical filtration; most commonly caused by dissolved organic matter, but may be produced by dissolved mineral matter. As measured in a water analysis, only the intensity of yellow color is reported.

	Color Throw	The discharge of color to the effluent of a filter or ion exchange system by any component. It usually occurs after a period of standing which allows slowly soluble colored matter to accumulate in the system.

	Column Operation	The process in which the solution to be treated is passed through a bed, or column (as in a tank), of filter media or ion exchanger; may be either upflow or downflow.

	Combined Available Chlorine	The chlorine present as chloramine or other chlorine derivatives in a water, but still available for disinfection and the oxidation of organic matter. Combined chlorine compounds are more stable than free chlorine forms, but are somewhat slower in disinfection action.

	Community Water System	A water system which supplies drinking water to 25 or more of the same people year-round in their residences.

	Compensated Hardness	A calculated value based on the total hardness, the magnesium to calcium ratio and the sodium concentration of a water. It is used to correct for the reductions in hardness removal capacity caused by these factors in zeolite exchange water softeners. No single method of calculation has been widely accepted.

	Compliance	The act of meeting all state and federal drinking water regulations.

	Composite Sample	A mixture of a number of single or "grab" samples, intended to produce a typical or average sample. May be made up of equal volumes of individual samples, or of single samples proportioned to variations in flow or usage.

	Concentration Factor	A number used to estimate the scaling potential in reverse osmosis systems when the TADS rejection is expected to exceed 90%; equal to the reciprocal of 1 minus the recovery ratio. When multiplied by the feed TADS, the result is the approximate waste water TADS. (See recovery, rejection.)

	Conductance	In water conditioning, the readiness of water to carry electricity; the reciprocal of electrical resistance. The unit of measure for conductance is the mho (reciprocal ohm). Used to approximate the dissolved solids content of water. (See conductivity, resistance, specific conductance.)

	Conductivity	The quality or power to carry electrical current; in water; related to the concentration of ions capable of carrying electrical current. (See conductance, electrolyte.)

	Connate Water	Water deposited simultaneously with rock and held with essentially no flow; usually occurs deep in the earth, and usually is high in minerals due to long contact.

	Contaminant	Anything found in water (including microorganisms, minerals, chemicals, radionuclides, etc.) which may be harmful to human health.

	Contamination	The presence of foreign matter in a substance which reduces the value of the substance, or interferes with its intended use.

	Conversion	See "recovery".

	Corrosion	The disintegration of a metal by electrochemical means.

	Crenothrix Polyspora	A genus of filamentous bacteria which utilize iron in their metabolism, and cause staining, plugging and taste and odor problems in water systems. (See iron bacteria.)

	Cross Connection	A direct link between a potable water system and a non-potable water system, which permits undesirable substances to be drawn into the potable water.

	Cross-Sectional Area	The area of a plane at a right angle to the direction of flow through a tank or vessel; often expressed in square feet, and related to the flow rate. (Example: 5 gallons per minute per square foot of ion exchanger bed area.)

	Cryptosporidium	A common intestinal parasite found in waters contaminated by sewerage or runoff containing animal waste. It causes diarrhea, nausea, and cramps. Individuals with weakened immune systems are at particular risk. Although resistant to chlorine and most oxidizing agents, it is effectively removed by filtration to 1 micrometer, and can be destroyed by boiling.

	Cryptosporidium	A microorganism commonly found in lakes and rivers which is highly resistant to disinfection. Cryptosporidium has caused several large outbreaks of gastrointestinal illness, with symptoms that include diarrhea, nausea, and/or stomach cramps. People with severely weakened immune systems (that is, severely immuno-compromised) are likely to have more severe and more persistent symptoms than healthy individuals.

	Cube	A slang expression sometimes used to mean a cubic foot of ion exchanger or filter media.

	Cubic Foot	The volume of a cube whose sides have the length of one foot. The common basis for the measurement of the volume of ion exchangers or loose filter media.

	Cycle	A series of events or steps which ultimately lead back to the starting point, such as the exhaustion-regeneration cycle of an ion exchange system.

	Cysts	Common cysts include Cryptosporidia and Giardia. Because cysts have a "hard shell," they are able to survive in hostile environments, such as the presence of chlorine or absence of water. It is because of this hard shell that they are hard to kill. Once the cyst is ingested, the shell is discarded and the organisims infect the intestines, causing diarrhea, headaches, abdominal cramps, nausea and vomiting.

	D.I. Or Di	Abbreviation for "deionization".

	Dechlorination	The removal of chlorine residual.

	Deionization	The removal of all ionized minerals and salts from a solution by a two-phase ion exchange process. 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. The term, commonly abbreviated as DI, is often used interchangeably with demineralization. (See demineralization, ion exchange.)

	Demineralization	The removal of ionized minerals and salts from a solution by a two-phase ion exchange procedure, similar to deionization, and the two terms are often used interchangeably. (See deionization, ion exchange.)

	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. (See specific gravity.)

	Detergent	Any material with cleaning powers, including soaps, synthetic detergents, many alkaline materials and solvents, and abrasives. In popular usage the term is often used to mean the synthetic detergents such as ABS of LAS. (See alkyl benzene sulfonate, linear alkyl sulfonate, soap.)

	Dialysis	The separation of components of a solution by diffusion through a semi-permeable membrane which is capable of passing certain ions or molecules while rejecting others. (See electrodialysis, semi-permeable membrane.)

	Diaphragm Pump	A type of 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 problems with packing and seals.

	Diatomaceous Earth	A processed natural material, the skeletons of diatoms, used as a filter medium.

	Diatomite	Another name for diatomaceous earth.

	Dielectric Fitting	A plumbing fitting made of, or containing, an electrical nonconductor, such as plastic; used to separate dissimilar metals in a plumbing system to control galvanic corrosion.

	Differential Pressure	See pressure differential.

	Digestion	The process in which complex materials are broken down into simpler substances; may be due to chemical, biological or a combination of reactions. (See sterilization.)

	Disinfectant	A chemical (commonly chlorine, chloramine, or ozone) or physical process (e.g., ultraviolet light) that kills microorganisms such as bacteria, viruses, and protozoa.

	Disinfection	A process in which vegetative bacteria are killed; may involve disinfecting agents such as chlorine, or physical processes such as heating. (See aerobic, anaerobic.)

	Dissociation	The separation of molecules into positively and negatively charged ions; occurs when salts dissolve in water. (See ionization.)

	Dissolved Solids	The weight of matter in true solution in a stated volume of water; includes both inorganic and organic matter; usually determined by weighing the residue after evaporation of the water at 105 or 180oC.

	Distillation	The process in which a liquid, such as water, is converted into its vapor state by heating, and the vapor cooled and condensed to the liquid state and collected; used to remove solids and other impurities from water; multiple distillations are required for extreme purity.

	Distribution System	A network of pipes leading from a treatment plant to customers' plumbing systems.

	Distributor	A device or system designed to produce even flow through all sections of an ion exchanger or filter bed, and to retain the media in the tank or vessel; usually installed at the top and bottom of loose media systems. (See collector.)

	Dolomite	A specific form of limestone containing chemically equivalent concentrations of calcium and magnesium carbonates; the term is sometimes applied to limestones with compositions similar to true dolomite.

	Domestic	A term sometimes applied to water conditioning equipment designed for household use.

	Downflow	A term designating the direction (down) in which water or a regenerant flows through an ion exchanger or filter during any phase of the operating cycle.

	Drain	A pipe or conduit in a building plumbing system which carries liquids to waste by gravity; sometimes the term is limited to liquids other than sewage.

	Drain Line	A tube or pipe from a water conditioning unit that carries backwash water, regeneration wastes and/or rinse water to a drain or waste system.

	Dynamic	Active, alive, or tending to produce motion, as opposed to static, resting or fixed.

	Dynamic System	A system or process in which motion occurs, or includes active forces, as opposed to static conditions with no motion.

	E. Coli	The common abbreviation of Escherichia Coli.

	Eductor	A device utilizing a nozzle and throat, installed in a stream of water to create a partial vacuum to draw air or liquid into the stream; commonly used to draw regeneration chemicals into an ion exchange water treatment system, such a softener or deionizer.

	Effective Size	A measure of the size of particles of ion exchanger or filter medium; defined as the diameter of a specific particle in a bed, batch or lot which has 10 percent smaller and 90 percent larger particles.

	Efficiency	The ratio of output per unit input or the effectiveness of performance of a system; in an ion exchange system, often expressed as the amount of regenerant required to produce a unit of capacity, such as the pounds of salt per kilograin of hardness removal.

	Effluent	The stream emerging from a unit, system or process, such as the softened water from an ion exchange softener.

	Ejector	A device which used a high velocity jet to entrain a gas or liquid in a stream of air or liquid. (See eductor.)

	Electrodialysis	A process in which a direct current is applied to a cell to draw charged ions through ion selective semipermeable membranes, thus removing the ions from the solution.

	Electrolysis	In general, the chemical change caused by the passage of an electric current, often a decomposition of a material; the decomposition of water into oxygen and hydrogen by the application of a direct current; the action in which one metal goes into solution in a galvanic cell at the junction between dissimilar metals in a water system. (See galvanic corrosion.)

	Electrolyte	A nonmetallic substance that carries an electric current, or a substance which, when dissolved in water, separates into ions which can carry an electric current. (See conductance, ionization.)

	Electron	A fundamental particle found in the atom which carries a single negative charge.

	Elution	The stripping of ions from an ion exchange material by other ions, either because of greater affinity or because of much higher concentration.

	Endpoint	The point at which a process is stopped because a predetermined value of a measurable variable is reached.

	Equilibrium	The state in which the action of multiple forces produce a stead balance.

	Equilibrium Reaction	A chemical reaction which proceeds primarily in one direction until the concentrations of reactants and products reach an equilibrium.

	Equivalent Weight	The weight in grams of an element, compound or ion which would react with or replace 1 gram of hydrogen; the molecular weight in grams divided by the valence.

	Erosion	The process in which material is worn away by a stream of air or liquid, often due to the presence of abrasive particles in the stream; a physical or mechanical wearing process rather than a chemical solution process.

	Escherichia Coli	One of the members of the coliform groups of bacteria indicating fecal contamination. (See fecal, coliform.)

	Exchange Velocity	The rate with which one ion is displaced from an ion exchange material in exchange for another ion.

	Exemption	State or EPA permission for a water system not to meet a certain drinking water standard. An exemption allows a system additional time to obtain financial assistance or make improvements in order to come into compliance with the standard. The system must prove that: (1) there are compelling reasons (including economic factors) why it cannot meet a MCL or Treatment Technique; (2) it was in operation on the effective date of the requirement, and (3) the exemption will not create an unreasonable risk to public health. The state must set a schedule under which the water system will comply with the standard for which it received an exemption.

	Exhaustion	The state of an ion exchange material that is no longer capable of effective function due to the depletion of the initial supply of exchangeable ions. (See ion exchange, endpoint.)

	Exposure	Contact between a person and a chemical. Exposures are calculated as the amount of chemical available for absorption by a person.

	Fecal	Matter containing or derived from animal or human wastes or feces.

	Filter	A device or system for the removal of solid particles (suspended solids).

	Filter Area	The effective area through which water passes through filter media, often expressed in square feet. (See cross sectional area.)

	Filter Medium	(See medium.)

	Filtrate	The effluent liquid from a filter.

	Fines	Extremely small particles of filter media or ion exchange material, often the result of breakage or chemical or physical deterioration.

	Finished Water	Water that has been treated and is ready to be delivered to customers.

	Fixed Solids	The suspended or dissolved solids remaining after ignition, usually at 600oCl; usually due to inorganic matter which is not volatilized at the ignition temperature.

	Fixture	In plumbing, a permanently installed device in which water is used, such as a faucet or toilet.

	Fixture Unit	An arbitrary unit assigned to different types of plumbing fixtures, and used to estimate flow rate requirements and drain capacity requirements.

	Floc	An agglomeration of finely divided suspended particles in a larger, usually gelatinous particle the result of physical attraction or adhesion to a coagulant compound.

	Flocculation	The process of causing a "floc" to form after treatment with a coagulant by gentle stirring or mixing. (See coagulation.)

	Flow Control	A device designed to limit or restrict the flow of water or regenerant; may include a throttling valve, an orifice of fixed diameter, or a pressure compensating orifice.

	Flow Rate	The quantity of water or regenerant which passes a given point in a specified unit of time, often expressed in gallons per minute.

	Fluoridation	The addition of a fluoride compound to a water supply for the reduction in incidence of dental caries.

	Flush Tank	A tank or chamber in which water is stored for rapid release.

	Flush Valve	A self-closing valve designed to release a large volume of water when tripped.

	Fma	Abbreviation for free mineral acidity (see mineral acidity).

	Fouling	The process in which undesirable foreign matter accumulates in a bed of water conditioning media, clogging pores and coating surfaces and thus inhibiting or retarding the proper operation of the bed.

	Free Available Chlorine	The concentration of residual chlorine present as dissolved gas, hypochlorous acid or hypochlorite, not combined with ammonia or in other less readily available form.

	Free Carbon Dioxide	Carbon dioxide present in water as the gas, or as carbonic acid, but not that combined in carbonates or bicarbonates.

	Free Chlorine	See free available chlorine.

	Free Mineral Acidity	See mineral acidity.

	Freeboard	The vertical distance between a bed of filter media or ion exchange material and the overflow or collector for backwash water; the height above the bed of granular media available for bed expansion during backwashing; may be expressed either as a linear distance or a percentage of bed depth.

	Gallionella Ferruginea	A genus of stalked, ribbon-like bacteria which utilize iron in their metabolism, and cause staining, plugging and odor problems in water systems. (See iron bacteria.)

	Gallon	A unit of liquid volume; the U.S. gallon has a volume of 231 cubic inches or 3.78533 liters; the British (Imperial) gallon has a volume of 277.418 cubic inches or 4.54596 liters.

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

	Galvanic Corrosion	The form of corrosion which occurs in a galvanic cell, in which one of the metals goes into solution; accelerated by high concentrations of dissolved minerals in water, which increases the electrical conductance; and elevated temperatures. (See corrosion, electrolyte.)

	Gate Valve	A valve with the closing element that is a disc which is moved across the stream, often in a groove or slot, for support against pressure.

	Gel Zeolite	A synthetic sodium aluminoscilicate ion exchanger.

	Giardia Lamblia	An intestinal parasite commonly found in water supplies originating in mountainous or wooded watersheds. It exists as a free-swimming protozoan-like organism in warm-blooded animals' intestines, causing chronic diarrhea, cramps, bloating and weight loss. Outside of the intestines, it forms a tough cyst that protects it until it finds a new host. Resistant to chlorine and most oxidizing agents, Giardia can be removed effectively through filtration below 1 micrometer.

	Giardia Lamblia	A protozoan frequently found in rivers and lakes, which can survive in water for 1 to 3 months, associated with the disease giardiasis. Ingestion of this protozoan in contaminated drinking water, exposure from person-to-person contact, and other exposure routes may cause giardiasis. The symptoms of this gastrointestinal disease may persist for weeks or months and include diarrhea, fatigue, and cramps.

	Globe Valve	A valve in which the closing element is a sphere, or a flat or rounded gasket, which is moved into or onto a round port.

	Gpg	Abbreviation for "grain(s) per gallon".

	Grab Sample	A single sample of material collected at one place and one time.

	Grain (Gr.)	A unit of eight equal to 1/7000th of a pound, or 0.0648 gram.

	Grain(S) Per Gallon (Gpg)	A common basis for reporting water analyses in the United States and Canada; one grain per U.S. gallon equals 17.12 milligrams per liter (mg/l) or parts per million (ppm). One grain per British (Imperial) gallon equals 14.3 milligrams per liter or parts per million.

	Gram (G)	The basic unit of weight (mass) of the metric system, originally intended to be the weight of 1 cubic centimeter of water at 4oC. (One pound is 454 grams.)

	Gram-Milliequivalent	The equivalent weight of a substance in grams, divided by one thousand.

	Gravimetric	Measurement of matter on the basis of weight.

	Greensand	A natural mineral, primarily composed of complex silicates, which possess ion exchange properties. (See manganese greensand, zeolite.)

	Ground Water	The water that systems pump and treat from aquifers (natural reservoirs below the earth's surface).

	Hardness	A characteristic of natural water due primarily to the presence of dissolved polyvalent (valence greater than 1) cations, such as calcium (Ca+2) and magnesium (Mg+2). Water hardness is responsible for most scale formation in pipes and water heaters, and forms insoluble "curd" when it reacts with soaps. Hardness is usually expressed in grains per gallon, parts per million, or milligrams per liter, all as calcium carbonate equivalent.

	Head	A measure of the pressure at a point in a water system, expressed in pounds per square inch, or in the height of a column of water which would produce the pressure. 1 psi equals 2.31 feet of head (water).

	Head Loss	The same as "pressure drop".

	Health Advisory	An EPA document that provides guidance and information on contaminants that can affect human health and that may occur in drinking water, but which EPA does not currently regulate in drinking water.

	High-Test Hypochlorite	A dry solid, largely calcium hypochlorite, used as a disinfecting agent; has excellent stability as long as kept dry.

	Home-Owned	A slang term sometimes applied to permanently installed household water conditioning equipment, as opposed to rental or portable exchange equipment.

	Hydration	The chemical combination of water into a substance.

	Hydraulic	Referring to water or other fluids in motion.

	Hydraulic Classification	A process in which particles of the same specific gravity may be graded according to size by backwashing or other relative upward flow of water, with the smallest particles tending to rise to the top of the bed, and largest particles tending to sink to the bottom, because of variations in weight to sur area ratios.

	Hydrogen Cycle	The cation exchange cycle in which the cation exchanger is regenerated with acid, and cations are removed from the solution treated, in exchange for hydrogen ions.

	Hydrogen Ion Concentration	The concentration of hydrogen ions in moles per liter of solution; often expressed as pH. (See pH.)

	Hydrogen Sulfide	This is not a routine test but is determined only upon request and on a separate special sample. It is a poisonous gas and will cause headache and nausea. It smells like "rotten eggs". It causes a black precipitate with many metals.

	Hydrologic Cycle	The water cycle, including precipitation of water from the atmosphere as rain or snow, flow of water over or through the earth, and evaporation or transpiration to water vapor in the atmosphere. Water evaporates from the earth and rises into the atmosphere where it forms clouds. In nature, this is where water is in its purest form. However, it does not stay that way for long. Its stay in the air is short. Water droplets forming in clouds, absorb particles and impurities found floating in the air.

	Hydrolysis	The reaction of a salt with water to form an acid and a base.

	Hydropneumatic System	A system utilizing both air and water in its operation, such as the pressure tank used with many well systems, which utilizes an air chamber to maintain pressure on the water when the pump is not operating.

	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 examined for leaks, distortion and/or mechanical failure.

	Hydroxide	A chemical compound containing hydroxyl (OH) ion. (See hydroxyl.)

	Hydroxyl	The OH anion which has a single negative charge, and provides the characteristics common to bases. (See base.)

	Hypochlorite	The OCL anion; calcium and sodium hypochlorite are commonly used as bleaches and disinfecting agents.

	Indicator	A material which can be used to show the endpoint of a chemical reaction, usually by a color change, or a chemical concentration by a depth or shade of color.

	Influent	The stream entering a unit, stream or process, such as the hard water entering an ion exchange water softener.

	Inorganic Contaminants	Mineral-based compounds such as metals, nitrates, and asbestos. These contaminants are naturally-occurring in some water, but can also get into water through farming, chemical manufacturing, and other human activities. EPA has set legal limits on 15 inorganic contaminants.

	Inorganic Matter	Matter which is not derived from living organisms and contains no organically produced carbon; includes rocks, minerals and metals.

	Installation	The process in which water conditioning equipment is connected into the water system, and a drain line provided where necessary. The term is also used to refer to the complete assembly of piping, valves, drain line, water conditioning unit and related equipment.

	Intermittent Flow	The term usually applied to the interrupted patterns of water usage; also used in reference to specific on-off flow patterns selected to test the performance of water conditioning equipment under standard conditions, which may or may not be similar to actual patterns of use of installed equipment.

	Ion	An atom or group of atoms which function as a unit, and have a positive (cation) or negative (anion) electrical charge, due to the gain or loss of one or more electrons. (See ionization.)

	Ion Exchange	A reversible process in which ions are released from an insoluble permanent material in exchange for other ions in a surrounding solution; the direction of the exchange depends upon the affinities of the ion exchanger for the ions present, and the concentrations of the ions in the solution. (See base exchange.)

	Ion Exchanger	A permanent, insoluble material which contains ions that will exchange reversibly with other ions in a surrounding solution. Both cation and anion exchangers are used in water conditioning. (See anion, cation, ion.)

	Ionization	The process in which atoms gain or lose electrons; sometimes used as synonymous with dissociation, the separation of molecules into charged ions in solution.

	Ionization Constant	A constant specific for each partially ionizable chemical compound to express the ratio of the concentration of ions from the compound to the concentration of un-ionized compound.

	Iron	An element often found in ground water. It is objectionable in water supplies because of the staining caused after oxidation (bleach) and precipitation, tastes, and unsightly colors produced when iron reacts with tannin in beverages such as coffee and tea.

	Iron Bacteria	Microorganisms which are capable of utilizing ferrous iron, either from the water or from steel pipe, in their metabolism, and precipating ferric hydroxide in the sheaths and gelatinous deposits. These organisms tend to collect in pipe lines and tanks during periods of low flow, and to break loose in slugs of turbid water to create staining, taste and odor problems. (See Crenothrix polyspora, Gallionella ferruginea.)

	Jackson Turbidity Unit	An obsolete unit of turbidity measurement based on a suspension of a specific type of silica with the turbidity measured in a Jackson Candle Turbidimeter (contract to "Nephelometric Turbidity Unit").

	Jtu	The abbreviation for "Jackson Turbidity Unit".

	Kilo	A prefix used to indicate 1000 of the succeeding unit. (Kilo is also sometimes used as an abbreviation for kilogram.)

	Kilograin(Kgr.)	One thousand grains. (See grain.)

	Kilogram (Kg.)	One thousand grams. (See gram.)

	Laminar Flow	The flow of fluid in which the flow paths are in smooth, parallel lines, with essentially no mixing and no turbulence.

	Langelier's Index	A calculated number used to predict whether or not a water will precipitate, be in equilibrium with, or dissolve calcium carbonate. It is sometimes erroneously assumed that any water which tends to dissolve calcium carbonate is automatically corrosive.

	Las	Abbreviation for "Linear Alkyl Sulfonate".

	Lead	This odorless and tasteless chemical can leach into water from the corrosion of household plumbing systems or from the erosion of natural deposits. According to the definition in California Proposition 65, may lead to elevated blood pressure levels and/or kidney damage in adults. If ingested regularly by children, lead may cause delays in physical or mental development.

	Leakage	The presence of a consistent concentration of ions in the effluent of an ion exchange system due to incomplete removal of the ions; caused by incomplete regeneration, excessive flow rates, low temperatures, the concentration or characteristics of the influent ions, or other factors. (See hardness leakage.)

	Lime	The common name for calcium oxide (CAO); hydrated lime is calcium hydroxide, Ca(OH)2.

	Lime Scale	Hard water scale containing a high percentage of calcium carbonate.

	Limestone	A sedimentary rock, largely calcium carbonate, and usually also containing significant amounts of magnesium carbonate.

	Linear Alkyl Sulfonate	A term applied to a family of straight chain chemical compounds, widely used as detergents; sometimes called "soft" detergents because they are more readily degraded to simpler substances by biological action than the previously used alkyl benzene sulfonate. (See detergent, alkyl benzene sulfonate.)

	Liter	The basic metric unit of volume; 3.785 liters equal 1 U.S. gallon; 1 liter of water weighs 1000 grams.

	M Alkalinity	Methyl orange alkalinity. (See total alkalinity.)

	Macroreticular	A term applied to ion exchange resins that have a rigid polymer porous network in which there exists a true pore structure even after drying. The pores are larger than atomic distances and are not a part of the gel structure.

	Magnesium	One of the elements in the earth's crust, the compounds of which when dissolved in water make the water hard. The presence of magnesium in water is a factor contributing to the formation of scale and insoluble soap curds.

	Manganese	An element sometimes found dissolved in ground water, usually with dissolved iron but in lower concentration; causes black stains and other problems similar to iron. It can be removed by a water softener or it can be precipitated by chlorine at a pH of 9.5 or above.

	Manganese Greensand	Greensand which has been processed to incorporate in its pores and on its surface the higher oxides of manganese. The product has a mild oxidizing power, and is often used in the oxidation and precipitation of iron, manganese and/or hydrogen sulfide, and their removal from water (see greensand, manganese zeolite).

	Manganese Zeolite	Synthetic gel zeolite which has been processed in the same manner as manganese greensand, and used for similar purposes.

	Maximum Contaminant Level (Mcl)	The highest level of a contaminant that EPA allows in drinking water. MCLs ensure that drinking water does not pose either a short-term or long-term health risk. EPA sets MCLs at levels that are economically and technologically feasible. Some states set MCLs which are more strict than EPA's.

	Maximum Contaminant Level Goal (Mclg)	The level of a contaminant at which there would be no risk to human health. This goal is not always economically or technologically feasible, and the goal is not legally enforceable.

	Mbas	Abbreviation for "Methylene Blue active Substance".

	Mcl	Abbreviation for "Maximum Contaminant Level"; the maximum allowable concentration of a contaminant in water as established in the U.S. EPA Drinking Water Regulations.

	Mechanical Filter	A filter primarily designed for the removal of suspended solid particles, as opposed to filters with additional capabilities.

	Media	The plural form of "medium".

	Medium	A material used in a filter bed to form a barrier to the passage of certain suspended solids or dissolved molecules.

	Methylene Blue Active Substances	Chemical compounds which react with methylene blue to form a blue compound which can be used to estimate the concentration by measurement of the depth of color. Substances measured include ABS and LAS types of detergents, thus the term is commonly used as an expression of detergent concentration. (See detergent.)

	Mg/L	The abbreviation for milligrams per liter.

	Micrometer	Formally known as micron. A linear measure equal to one millionth of a meter or .00003937 inch. The symbol for the micrometer is "um".

	Micron	See micrometer.

	Micron Rating	The term applied to a filter medium to indicate the particle size above which all suspended solids will be removed throughout the rated capacity. As used in industry standards, this is an "absolute" not "nominal" rating.

	Microorganisms	Tiny living organisms that can be seen only with the aid of a microscope. Some microorganisms can cause acute health problems when consumed in drinking water. Also known as microbes.

	Mil	One thousandth of an inch.

	Milli	The prefix used with units of measure to indicate one thousandth of the unit. Example: a milliliter is one thousandth of a liter.

	Milligram Per Liter (Mg/L)	A unit concentration of matter used in reporting the results of water and waste water analyses. In dilute water solutions, it is practically equal to the part per million, but varies from the ppm in concentrated solutions such as brine. As most analyses are performed on measured volumes of water, the mg/l is a more accurate expression of the concentration, and is the preferred unit of measure.

	Millimicron	(archaic) See "nanometer".

	Mineral	A term applied to inorganic substances such as rocks and similar matter found in the earth strata, as opposed to organic substances such as plant and animal matter. Minerals normally have definite chemical composition and crystal structure. The term is also applied to matter derived from minerals, such as the inorganic ions found in water. The term has been applied to ion exchangers, stemming from the early use of natural zeolite. The term is inappropriate to the modern organic ion exchange resins.

	Mineral Acidity	Acidity due to the presence of inorganic acids such hydrochloric, sulfuric and nitric acids, as opposed to acidity due to carbonic acid or organic acids.

	Mole	6.02 x 1023 atoms of an element or 6.02 x 1023 molecules of a chemical compound. The weight of one mole of an element is equal to its atomic weight in grams; the weight of one mole of a compound is equal to its molecular weight in grams.

	Molecule	The simplest combination of atoms that will form a specific chemical compound; the smallest particle of a substance which will still retain the essential composition and properties of that substance, and which can be broken down only into atoms and simpler substances.

	Monitoring	Testing that water systems must perform to detect and measure contaminants. A water system that does not follow EPA's monitoring methodology or schedule is in violation, and may be subject to legal action.

	Most Probable Number (Mpn)	The term used to indicate the number of microorganisms which, according to statistical theory, would be most likely to produce the results observed in certain bacteriological tests; usually expressed as a number per 100 ml of water.

	Mpn	The abbreviation for "most probable number".

	Nanometer	Abbreviated "nm", a unit of length equal to one thousandth of a micrometer. Often used to express the wavelength of ultraviolet light and the colors of visible light in colorimetric analytical procedures.

	Negative Charge	The electrical charge on an electrode or ion in solution, due to the presence of an excess of electrons. (See electron, anion.)

	Negative Head	A condition of negative pressure or partial vacuum.

	Negative Pressure	A pressure below that of the surrounding atomspheric pressure at a specific point; a partial vacuum.

	Nephelometric Turbidity Unit	An arbitrary unit of measuring the turbidity in water by the light scattering effect of fine suspended particles in a light beam (contrast to "Jackson Turbidity Unit").

	Neutral	In electrical systems, the term used to indicate neither an excess nor a lack of electrons; a condition of balance between positive and negative charges. In chemistry, the term used to indicate a balance between acids and bases; the neutral point on the pH scale is 7.0, indicating the presence of equal numbers of free hydrogen (acidic) and hydroxide (basic) ions.

	Neutralization	The addition of either an acid or a base to a solution as required to produce a neutral solution. The use of alkaline or basic materials to neutralize the acidity of some waters is a common practice in water conditioning.

	Neutralizer	A common designation for alkaline materials such as calcite (calcium carbonate) or magnesia (magnesium oxide) used in the neutralization of acid waters.

	Nitrates	Inorganic compounds that can enter water supplies from fertilizer runoff and sanitary wastewater discharges. Nitrates in drinking water are associated with methemoglobinemia, or blue baby syndrome, which results from interferences in the bloods ability to carry oxygen.

	Noncarbonate Hardness	Water hardness due to the presence of compounds such as calcium and magnesium chlorides, sulfates or nitrates; the excess of total hardness over total alkalinity.

	Non-Transient, Non-Community Water System	A water system which supplies water to 25 or more of the same people at least six months per year in places other than their residences. Some examples are schools, factories, office buildings, and hospitals which have their own water systems.

	Normal Solution	A solution containing a gram equivalent weight of a substance in one liter of solution. (See equivalent weight.)

	Ntu	Abbreviation for "Nephelometric Turbidity Unit".

	Odors	Are self-descriptive. Odors are sometimes transmitted to the sample by the shipping container when it is not a standard Culligan sample bottle.

	Operating Pressure	The range of pressure, usually expressed in pounds per square inch, over which a water conditioning device or water system is designed to function.

	Organic Contaminants	Carbon-based chemicals, such as chlorohydrocarbons, solvents and pesticides, which can get into water through runoff from cropland or discharge from factories. EPA has set legal limits on 56 organic contaminants.

	Organic Matter	Substances of or derived from plant or animal matter. Organic matter is characterized by its carbon-hydrogen structure.

	Osmosis	A process of diffusion of a solvent such as water through a semipermeable membranae which will transmit the solvent but impede most dissolved substances. The normal flow of solvent is from the dilute solution to the concentrated solution in an attempt to bring the solutions on both sides of the membranae to equilibrium. (See equilibrium, reverse osmosis.)

	Oxidation	A chemical process in which electrons are removed from an atom, ion, or compound; causing the substance's valence to increase. The addition of oxygen is a specific form of oxidation; combustion is an extremely rapid form of oxidation, while the rusting of iron is a slow form. Whenever oxidation occurs, an offsetting reduction reaction must occur. (See reduction.)

	Ozone	An unstable form of oxygen (O3), which can be generated by an electrical discharge through air or regular oxygen. It is a strong oxidizing agent and has been used in water conditioning as a disinfectant.

	P Alkalinity	Phenolphthalein alkalinity of a water as determined by titration with standard acid solution to the phenolphthalein endpoint (pH approx. 8.3). Includes carbonate and hydroxide alkalinity. (See total alkalinity.)

	P.E.	The abbreviation for "portable exchange".

	Particle Size	As used in industry standards, the size of a particle suspended in water as determined by its smallest dimension, usually expressed in micrometers.

	Parts Per Million (Ppm)	A common basis for reporting the results of water and waste water analyses, indicating the number of parts by weight of a dissolved or suspended constituent, per million parts by weight of water or other solvent. In dilute water solutions, one part per million is practically equal to one milligram per liter, which is the preferred unit. 17.12 ppm equals one grain per U.S. gallon.

	Pathogen	An organism which may cause disease.

	Per Capita	Per person; generally used in expressions of water use, gallons per capita per day (gpcd).

	Percentage Values	These are needed to calculate specific resin capacities for this water supply. They are also to calculate DI water quality.

	Permanent Hardness	Water hardness due to the presence of the chlorides and sulfates of calcium and magnesium, which will not precipitate by boiling. This term is largely replaced by "noncarbonate hardness". (See noncarbonate hardness.)

	Permanganate	Generally refers to potassium permanganate, a chemical compound used in water treatment. (See potassium permanganate.)

	Ph	The negative logarithm of the hydrogen ion concentration. The pH scale ranges from zero to 14 with 7 as the neutral point, indicating the presence of equal concentrations of free hydrogen and hydroxide ions. pH values below 7.0 indicate acidity, with 0 most acid; pH values above 7 indicate basicity, with 14 most basic, or alkaline.

	Phreatophyte	A plant which takes its water from the zone of saturation or the capillary fringe of ground water. Excessive growths of phreatophytes are undesirable in some areas since they may consume large quantities of scarce water.

	Physical Stability	A measure of the ability of an ion exchanger or filter medium to resist breakdown by physical forces such as friction, high temperatures and crushing to which it may be subjected in use.

	Pk	The reciprocal of the logarithm of the ionization constant of a chemical compound.

	Poh	The negative logarithm of the hydroxyl ion concentration. The pOH is related to pH by the expression: pH + pOH = 14. (See pH.)

	Point-Of-Entry Water Treatment	Refers to devices used in the home where water pipes enter to provide additional treatment of drinking water used throughout the home.

	Point-Of-Use Water Treatment	Refers to devices used in the home or office on a specific tap to provide additional drinking water treatment.

	Pollution	"Pollution is an impairment of quality such that it interferes with the intended usages." (House Report 2021.)

	Population Equivalent	A unit of measure used to express the strength of waste water from any source by comparison to the strength and volume of normal household waste water. The figure of 0.17 pound of BOD per capita per day is often used as a base figure for calculations.

	Porosity	A measure of the volume of internal pores, or voids, in ion exchangers and filter media; sometimes expressed as a ratio to the total volume of the medium. (See void volume.)

	Positive Charge	The net electrical charge on an electrode or ion in solution due to the removal of electrons. (See electron, cation.)

	Postchlorination	The application of chlorine to a water following other water treatment processes. (See prechlorination.)

	Potable Water	Water which is suitable for human consumption.

	Potassium Permanganate	An oxidizing chemical commonly used in processes for removing iron, hydrogen sulfide and manganese.

	Ppm	The abbreviation for "parts per million".

	Prechlorination	The application of chlorine to a water prior to other water treatment processes. (See postchlorination.)

	Precipitate	To cause a dissolved substance to form a solid particle which can be removed by settling or filtering, such as in the removal of dissolved iron by oxidation, precipitation and filtration. The term is also used to refer to the solid formed, and to the condensation of water in the atmosphere to form rain or snow.

	Precoat	The application of a granular filter medium, such as diatomaceous earth or powdered activated carbon to a membrane or screen or other filtration surface, prior to the service cycle of a filter.

	Pressure Differential	A difference or change in pressure detected between two points in a system due to differences in elevation and/or pressure drop due to flow.

	Pressure Drop	A decrease in water pressure during flow due to internal friction between molecules of water, and external friction due to irregularities or roughness in surfaces past which the water flows.

	Primacy State	A State that has the responsibility and authority to administer EPA's drinking water regulations within its borders. The State must have rules at least as stringent as EPA's.

	Public Notification	An advisory that EPA requires a water system to distribute to affected consumers when the system has violated MCLs or other regulations. The notice advises consumers what precautions, if any, they should take to protect their health.

	Public Water System (Pws)	Any water system which provides water to at least 25 people for at least 60 days annually. There are more than 170,000 PWSs providing water from wells, rivers and other sources to about 250 million Americans. The others drink water from private wells. There are differing standards for PWSs of different sizes and types.

Quaternary Ammonium

A basic chemical group [N(CH3)3+] which provides the site of activity of certain anion exchange resins.

	R. O.	The abbreviation for "reverse osmosis".

	Radionuclides	Elements that undergo a process of natural decay. As radionuclides decay, they emit radiation in the form of alpha or beta particles and gamma photons. Radiation can cause adverse health effects, such as cancer, so limits are placed on radionuclide concentrations in drinking water.

	Rated Capacity	The basis for calculating the period of time, or number of gallons delivered by a water softener, filter, or deionizer, between regenerations or servicing, as determined under specific test conditions. (See rated in-service life, rated softener capacity.)

	Rated In-Service Life	The length of time or total gallons delivered between servicing of the media in a filter as determined under standard test conditions.

	Rated Pressure Drop	The pressure drop of a water softener or filter at the rated service flow, with clean water at a temperature of 60oF, with a freshly regenerated and/or backwashed softener or filter, as determined under standard test conditions.

	Rated Service Flow	The manufacturer's specified maximum flow rate at which a water softener will deliver soft water, or a filter will deliver quality water as specified for its type, as determined under standard test conditions. A manufacturer may also specify a minimum flow rate or a range of service flows.

	Rated Softener Capacity	A water softener capacity rating based on grains of hardness removed while producing soft water between successive regenerations, and related to the pounds of salt required for each regeneration, as determined under standard test conditions.

	Raw Water	Untreated water, or any water before it reaches a specific water treatment device or process.

	Raw Water	Water in its natural state, prior to any treatment for drinking.

	Recovery	In reverse osmosis processes, indicates the amount of product water taken from the feed water stream; expressed as a percentage of product water flow rate to feed water flow rate. (See concentration factor.)

	Red Water	Water which has a reddish or brownish appearance due to the presence of precipitated iron and/or iron bacteria.

	Reduction	A chemical process in which electrons are added to an atom, ion or compound, causing the substance's valence to decrease. Whenever reduction occurs, an off-setting oxidation reaction must occur. (See oxidation.)

	Regenerant	A solution of a chemical compound used to restore the capacity of an ion exchange system. Sodium chloride brine is used as a regenerant for ion exchange water softeners, and acids and bases are used as regenerants for the cation and anion resins used in demineralization.

	Regeneration	The process of restoring an ion exchange medium to a usable state after exhaustion. In general, it includes the backwash, regenerant introduction and fresh water rinse steps necessary to prepare a water softener exchange bed for service. Specifically, the term may be applied to the step in which the regenerant solution is passed through the exchanger bed (salt brine for softeners, acid and bases for deionizers.

	Regeneration Level	The quantity of regenerant used in the regeneration of an ion exchange unit or system, usually expressed in pounds per regeneration and/or pounds per regeneration per cubic foot of ion exchanger.

	Rejection	In reverse osmosis processes, the degree of removal of dissolved salts from the feed water as it passed through a semipermeable membrane (also called "salt rejection"); expressed as a percentage of the feed water TDS. (See total dissolved solids.)

	Residual	The amount of a specific material remaining in the water following a water treatment process; may refer to material remaining as a result of incomplete removal (see leakage), or to material meant to remain in the treated water. (See residual chlorine.)

	Residual Chlorine	Chlorine remaining in a treated water after a specified period of contact time to provide continuing protection throughout a distribution system; the difference between the total chlorine added, and that consumed by oxidizable matter. (See combined available chlorine, free available chlorine.)

	Resin	Synthetic organic ion exchange material, such as the high capacity cation exchange resin widely used in water softeners.

	Resistance	In water conditioning, the opposition offered by water to the flow of electricity through it; the reciprocal of electrical conductance. The unit of measurement for electrical resistance is the Ohm. Electrical resistance can be used to approximate the mineral content, or lack of it, in high quality water. (See conductance.)

	Resistivity	A capacity for resisting the flow of electricity. (See resistance.)

	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	(R.O.) A process that reverses, by the application of pressure, the natural process of osmosis so that water passed from the more concentrated to the more dilute solution through a semipermeable membrane, thus producing a stream of water up to 98% free of dissolved solids.

	Rinse	That portion of the regeneration cycle of an ion exchanger in which fresh water is passed through the column to remove spent and excess regenerant, prior to placing the system in service.

	Risk	The potential for harm to people exposed to chemicals. In order for there to be risk, there must be hazard and there must be exposure.

	Saline Water	Water containing an excessive amount of dissolved salts, usually over 5,000 mg/l.

	Salt	In chemistry, the term is applied to a class of chemical compounds which can be formed by the neutralization of an acid with a with a base; the common name for the specific chemical compound sodium chloride used in the regeneration of ion exchange water softeners.

	Salt Splitting	The process in which neutral salts in water are converted to their corresponding acids or bases by ion exchange resins containing strongly acidic or strongly basic functional groups.

	Sample	The water that is analyzed for the presence of EPA-regulated drinking water contaminants. Depending on the regulation, EPA requires water systems and states to take samples from source water, from water leaving the treatment facility, or from the taps of selected consumers.

	Sanitary Survey	An on-site review of the water sources, facilities, equipment, operation, and maintenance of a public water systems for the purpose of evaluating the adequacy of the facilities for producing and distributing safe drinking water.

	Saponification	The process in which a fatty acid is neutralized with an alkali or base to form a soap.

	Scale	A deposit of mineral solids on the interior surfaces of water lines and containers, often formed when water containing the carbonates or bicarbonates of calcium and magnesium is heated.

	Secondary Drinking Water Standards	Non-enforceable federal guidelines regarding cosmetic effects (such as tooth or skin discoloration) or aesthetic effects (such as taste, odor, or color) of drinking water.

	Sedimentation	The process in which solid suspended particles settle out of water, usually when the water has little or no movement. Also called "settling".

	Semipermeable Membrane	Typically a thin, organic film which allows the passage of some ions or materials while preventing the passage of others. Some membranes will only allow the passage of cations. (See electrodialysis.) Some membranes reject most dissolved substances, but allow the passage of water. (See reverse osmosis.)

	Septic	A condition existing during the digestion of organic matter, such as in sewage, by anaerobic bacteria in the absence of air. A common process for the treatment of household sewage in septic tanks, and in municipal sewage treatment in specially designed digester.

	Sequestering Agent	A chemical compound sometimes fed into water to tie up undesirable ions, keep them in solution, and eliminate or reduce the normal effects of the ions. For example, polyphosphate can sequester hardness and prevent reactions with soap. (See cheating agent.)

	Sequestration	A chemical reaction in which certain ions are bound into a stable, water soluble compound, thus preventing undesirable action by the ions. (See chelate.)

	Service Run	That portion of the operating cycle of a water conditioning unit in which treated water is being delivered, as opposed to the period when the unit is being backwashed, recharged or regenerated.

	Service Unit	A term sometimes applied to softeners or filters which are regenerated or backwashed at a central point, then transported to the point of use for connection to the water system. (See portable exchange.)

	Shielded	The separation of metallic parts by an electrical nonconductor; insulated by other than an air gap.

	Silica Gel Or Siliceous Gel	A synthetic hydrated sodium aluminosilicate with ion exchange properties, once widely used in ion exchange water softeners. (See zeolite, gel zeolite.)

	Sludge	The semi-fluid solid matter collected at the bottom of a system tank or watercourse, as a result of the sedimentation or settling of suspended solids or precipitates.

	Slug	An abnormally high concentration of an undesirable substance which passes through a water system, usually brief or intermittent in nature, and often related to an upset of a system. For example, a slug of iron may occur during high flow which disturbs and suspends previously deposited iron precipitates.

	Soap	One of a class of chemical compounds which possesses cleansing properties; formed by the reaction of a fatty acid with a base or alkali. Sodium and potassium soaps are soluble and useful, but can be converted to insoluble calcium and magnesium soaps (curd) by the presence of these hardness ions in water.

	Soda Ash	the common name for sodium carbonate, Na2CO3, a chemical compound used as an alkalinity builder in some soap and detergent formulations to neutralize acid water, and in the lime-soda water treatment process.

	Sodium	An ion found in natural water supplies, and introduced to water in the ion exchange water softening process. Sodium compounds are highly soluble, and do not react with soaps or detergents.

	Sodium Chloride	The chemical name for common salt, widely used in the regeneration of ion exchange water softeners.

	Sodium Cycle	the cation exchange process in which sodium on the ion exchange resin is exchanged for hardness and other ions in water. Sodium chloride is the common regenerant used in this process.

	Soft Water	Any water which contains less than 1.0 gpg (17.1 mg/l) of hardness minerals, expressed as calcium carbonate.

	Softened Water	Any water that is treated to reduce hardness minerals to 1.0 gpg (17.1 mg/l) or less, expressed as calcium carbonate.

	Sole Source Aquifer	An aquifer that supplies 50 percent or more of the drinking water of an area.

	Solute	The substance which is dissolved in and by a solvent. Dissolved solids, such as the minerals found in water, are solutes.

	Solution Feeder	A device, such as a power driven pump or an eductor system, designed to feed a solution of a water treatment chemical into the water system, usually in proportion to flow. (See chemical feeder.)

	Solvent	The liquid, such as water, in which other materials (solutes) are dissolved. (See solute.)

	Source Water	Water in its natural state, prior to any treatment for drinking.

	Specific Conductance	The measure of the electrical conductance of water or a water solution at a specific temperature, usually 25oC. (See resistance.)

	Specific Gravity	The ratio of the weight of a specific volume of a substance compared to the weight of the same volume of pure water at 4oC.

	Specific Resistance	The measure of the electrical resistance of water or a water solution at a specific temperature, usually 25oC. (See resistance.)

	Sphericity	A measure of the roundness and wholeness of an ion exchange resin bead.

	Spore	In general, specialized reproductive bodies or resting cells. In water bacterial "spores" resist adverse conditions which would readily destroy the parent organism.

	Stability Index	See Langelier's Index.

	Standard Methods	The abbreviation for the name of the reference book "Standard Methods for the Examination of Water and Wastewater", widely used in water and waste water testing and analysis.

	Static	Fixed in position, resting, or without motion, as opposed to dynamic or moving.

	Static System	A system or process in which the reactants are not flowing or moving. (See dynamic system.)

	Sterilization	A process in which all living organisms are destroyed. (See disinfection.)

	Strong Base Load Factor Z	Is the total exchangeable anions. Thus it is the sum of total anions (which equals the Y factor) plus silica, plus carbon dioxide (not carbonic acid formed). 35 gpg is considered upper limit for DI applications.

	Sulfate	In the range of 30 gpg, sulfate salts can cause laxative effects and medicinal taste. In high concentration with high calcium hardness, a white insoluble compound is formed that is difficult to remove.

	Sulfate-Reducing Bacteria	A group of bacteria which are capable of reducing sulfates in water to hydrogen sulfide gas, thus producing obnoxious tastes and odors. These bacteria have no sanitary significance, and are classed as nuisance organisms.

	Sulfonic Acid	A specific acidic group (SO3H) which gives certain cation exchange resins their ion exchange capability.

	Sulfur	A yellowish solid element. The term is also commonly used to refer to water containing hydrogen sulfide gas.

	Superchlorination	The addition of excess amounts of chlorine to a water supply to speed chemical reactions or insure disinfection with short contact time. The chlorine residual following superchlorination is high enough to be unpalatable, and thus dechlorination is commonly employed before the water is used.

	Supernatant	The clear liquid lying above a sediment or precipitate.

	Surface Tension	The result of attraction between molecules of a liquid which causes the surface of the liquid to act as a thin elastic film under tension. Surface tension causes water to form spherical drops, and to reduce penetration into fabrics. Soaps, detergents and wetting agents reduce surface tension and increase penetration by water.

	Surface Water	The water that systems pump and treat from sources open to the atmosphere, such as rivers, lakes, and reservoirs.

	Surface-Active Agent	The material in a soap or detergent formulation which promotes the penetration of the fabric by water, the loosening of the soil from surfaces, and the suspension of many soils; the actual cleaning agent in soap and detergent formulations.

	Surfactant	A contraction of the term "surface-active agent".

	Suspended Solids	Solid particles in water which are not in solution.

	Swelling	In the water treatment context, the expansion of certain ion exchange resins when converted into specific ionic states.

	Syndet	A contraction of the term "synthetic detergent".

	Synthetic Detergent	A synthetic cleaning agent, such as linear alkyl sulfonate and alkyl benzene sulfonate. Synthetic detergents react with water hardness, but the products are soluble.

	Tds	The abbreviation for "total dissolved solids".

	Temporary Hardness	Water hardness due to the presence of calcium and magnesium carbonates and bicarbonates, which can be precipitated by heating the water. Now largely replaced by the term "carbonate hardness". (See carbonate hardness, permanent hardness.)

	Threshold	A very low concentration of a substance in water. The term is sometimes used to indicate the concentration which can just be detected.

	Throughput Volume	The amount of solution passed through an ion exchange bed before the ion exchanger is exhausted.

	Titration	An analytical process in which a standard solution in a calibrated vessel is added to a measured volume of sample until an endpoint, such as a color change, is reached. From the volume of the sample and the volume of standard solution used, the concentration of a specific material may be calculated.

	Total Acidity	The total of all forms of acidity, including mineral acidity, carbon dioxide, and acid salts. Total acidity is usually determined by titration with a standard base solution to the phenolphthalein endpoint (pH 8.3). (See acidity.)

	Total Alkalinity	The alkalinity of a water as determined by titration with standard acid solution to the methyl orange endpoint (pH approximately 4.5); sometimes abbreviated as "M" alkalinity". Total alkalinity includes many alkalinity components, such as hydroxides, carbonates, and bicarbonates. (see alkalinity.)

	Total Cations	This is the sum of Ca + Mg _ Na + K all reported in gpg as CaCO3. These are "positive" ions and are generally metals. Total cations should always equal total anions.

	Total Chlorine	The total concentration of chlorine in a water, including combined and free chlorine. (See combined available chlorine, free available chlorine.)

	Total Coliform	Bacteria that are used as indicators of fecal contaminants in drinking water.

	Total Dissolved Solids (Tds)	The weight of solids per unit volume of water which are in true solution, usually determined by the evaporation of a measured volume of filtered water, and determination of the residue weight.

	Total Hardness	The sum of all hardness constituents in a water, expressed as their equivalent concentration of calcium carbonate. Primarily due to calcium and magnesium in solution, but may include small amounts of metals such as iron, which can act like calcium and magnesium in certain reactions. (See hardness.)

	Total Solids	the weight of all solids, dissolved and suspended, organic and inorganic, per unit volume of water; usually determined by the evaporation of a measured volume of water at 105oC in a pre-weighted dish.

	Toxic	Having an adverse physiological effect on humans or other desirable organisms.

	Toxicity	The property of a chemical to harm people who come into contact with it.

	Trace	A very small concentration of a material, high enough to be detected but too low to be measured by standard analytical methods.

	Transient, Non-Community Water System	A water system which provides water in a place such as a gas station or campground where people do not remain for long periods of time. These systems do not have to test or treat their water for contaminants which pose long-term health risks because fewer than 25 people drink the water over a long period. They still must test their water for microbes and several chemicals.

	Transpiration	The process in which living plants release water vapor into the atmosphere, a significant part of the hydrologic cycle.

	Treatment Technique	A specific treatment method required by EPA to be used to control the level of a contaminant in drinking water. In specific cases where EPA has determined it is not technically or economically feasible to establish an MCL, EPA can instead specify a treatment technique.

	Tuberculation	The process in which blister-like growths of metal oxides develop in pipes as a result of the corrosion of the pipe metal. Iron oxide tubercles often develop over pits in iron or steel pipe, and can seriously restrict the flow of water.

	Turbidity	A measure of the cloudiness in water, the result of finely divided particulate matter suspended in water; usually reported in arbitrary units determined by measurements of light scattering. (See Nephelometric Turbidity Unit.)

	Turbidity	The cloudy appearance of water caused by the presence of tiny particles. High levels of turbidity may interfere with proper water treatment and monitoring.

	Turbulent Flow	A type of flow characterized by cross currents and eddies, as opposed to laminar or streamlined flow. Turbulence may be caused by surface roughness or protrusions in pipes, bends and fittings, changes in channel size, or excessive flow rates; turbulence significantly increases pressure drops.

	Unaccounted-For Water	A term used in municipal water systems to describe the difference between the water produced and that metered and sold. It usually includes losses due to leakage, water used for fire fighting, public sprinkling and other municipal purposes, and usually ranges from 10 to 35 percent of the water produced.

	Uniformity Coefficient	A measure of the variation in particle sizes of ion exchange resins and filter media. It is defined as the ratio of the size of particle which has 60 percent of the material finer than itself, to the size of the particle which has 10 percent finer than itself.

	Upflow	A term used to indicate the direction (up) in which water or regenerant flows through an ion exchanger or filter media bed during any phase of the operating cycle.

	Usepa	The abbreviation for "United States Environmental Protection Agency".

	Usphs	The abbreviation for "United States Public Health Service".

	Vacuum Breaker	A mechanical device which automatically vents a water line to the atmosphere when subjected to a partial vacuum, thus preventing back-flow. (See back-flow, air gap, back-flow preventer.)

	Valence	A small positive or negative whole number, also called oxidation number, which indicates the net number of electrons gained or lost in the formation of an ion, or the number of electrons the substance can donate or accept in a chemical reaction, and thus the numbers of each kind of ion necessary for a balanced chemical reaction. For example, two hydrogen ions (each with a valence of +1) must be present for each ion of oxygen (-2) to form a molecule of water (H2O).

	Variance	State or EPA permission not to meet a certain drinking water standard. The water system must prove that: (1) it cannot meet a MCL, even while using the best available treatment method, because of the characteristics of the raw water, and (2) the variance will not create an unreasonable risk to public health. The State or EPA must review, and allow public comment on, a variance every three years. States can also grant variances to water systems that serve small populations and which prove that they are unable to afford the required treatment, an alternative water source, or otherwise comply with the standard.

	Viable	Alive and capable of continued life.

	Violation	A failure to meet any state or federal drinking water regulation.

	Virus	The smallest form of life known to be capable of producing disease or infection, usually considered to be of large molecular size. They multiply by assembly of component fragments in living cells, rather than by cell division, as do most bacteria.

	Viscosity	The resistance of fluids to flow, due to internal forces and friction between molecules, which increases as temperature decreases.

	Void Volume	The volume of the spaces between particles of ion exchanger, filter media, or other granular material; often expressed as a percentage of the total volume occupied by the material.

	Volatile	Capable of vaporization at a relatively low temperature.

	Volatile Organic Chemicals (V.O.C.'S)	Chemicals that, as liquid, evaporate into the air.

	Volatile Solids	Matter which remains as a residue after evaporation at 105 or 180oC, but which is lost after ignition at 600oC. Includes most forms of organic matter.

	Volitile Organic Chemicals (Voc)	VOCs are a category of cantaminants. These chemicals, which include tetrachloroethylene, benzene and xylenes, are used in solvents, cleaners and degreasers used in many industrial and household products. When spilled or dumped, a portion of VOCs enter the ground and may eventually reach the water table. According to the EPA, health effects of VOCs include liver, kidney or central nervous system problems. Some VOCs are also suspected carcinogens.

	Volumetric	Referring to measurement by volume rather than weight. (See gravimetric.)

	Vulnerability Assessment	An evaluation of drinking water source quality and its vulnerability to contamination by pathogens and toxic chemicals.

	Water Conditioning	Virtually any form of water treatment designed to improve the aesthetic quality of water by the neutralization, inhibition or removal of undesirable substances. (Not health related.)

	Water Cycle	See hydrologic cycle.

	Water Hammer	A shock wave or series of waves produced by the abrupt acceleration or deceleration of water flow, due to inertia. Water hammer may produce instantaneous pressures many times the normal pressure.

	Water Softening	The removal of calcium and magnesium, the ions which are the principle cause of hardness, from water.

	Water Table	The level of the top of the zone of saturation, in which free water exists in the pores and crevices of rocks and other earth strata.

	Watershed	The land area from which water drains into a stream, river, or reservoir.

	Weak Base Load Faction X	Is referred to as the "Theoretical Mineral Acidity (TMA). It is the sum of the chloride, sulfate, and nitrate.

	Wellhead Protection Area	The area surrounding a drinking water well or well field which is protected to prevent contamination of the well(s).

		No terms starting with X

		No terms starting with Y

	Zeolite	A group of hydrated sodium aluminosilicates, either natural or synthetic, with ion exchange properties. (See gel zeolite, greensand.)

	Zeolite Softening	The removal of calcium and magnesium by ion exchange using natural or synthetic zeolite. The term is sometimes used to refer to all ion exchange softening processes, even though organic ion exchange resins, not inorganic zeolites, are in most common use today.

	Zero Soft	Water with a total hardness less than 1.0 grain per U.S. gallon, as calcium carbonate.

	Zone Of Aeration	The layer in the ground above an aquifer where the available voids are filled with air. Water falling on the ground percolates through this zone on its way to the aquifer.

	Zone Of Saturation	The layer in the ground in which all of the available voids are filled with water.

Water Glossary

Have a question? We're here to help!

Your Account

Policies

Resources