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.


Cellulose acetate


Carcinogen Assessment Group


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.


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.


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


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


SEE lime


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

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.


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.

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.

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).


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.


The CO32- ion.

Carbonate Alkalinity

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

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.


Any substance which tends to produce cancer in an organism.




SEE Entrainment


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.

CAS Registration Number

A number assigned by the Chemical Abstracts Service to identify a chemical.


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.


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


To be acted upon by a catalyst


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.


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 exchanger

SEE cation exchange resin

Cation Membrane

SEE Ion Exchange Membrane

Cationic Polymer

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


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


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


SEE Centigrade


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


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.


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.


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


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.


colony-forming units

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.


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.


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.


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 manufacturer’s claim that is based on reduction in concentration of an unwanted contaminant by a chemical means. Examples would include ion exchange, oxidation, and adsorption.

Chemical Feeder or Feed Pump

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.


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.


A component (generally a heat exchanger) designed to remove heat from a gas or liquid stream.

Chisel Plowing

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.


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 (SO42- ), 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.


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.


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.


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


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)).


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


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.


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

Chronic Exposure

Long-term, low-level exposure to a toxic chemical.

Circle of Influence

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


The complete path of an electric current, including the generating apparatus or other source; or, a specific segment or section of the complete path.

Circuit Breaker

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


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


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.


SEE hydraulic classification


A type of naturally-occurring hydrated aluminum silicate Al2O3SiO2 x 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.


Cyanobacteria-like bodies

Clear water iron

SEE ferrous iron

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.

Clinical Studies

Studies of humans suffering from symptoms induced by chemical exposure.

Club Soda

Soda water to which additional mineral salts have been added.


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


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.


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.


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


Chemical oxygen demand


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.

coliform organism

See colloids


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.


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.


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.


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.


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 <b>sequestration</b>.


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


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


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.


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.


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.).


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.


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).


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.


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.


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.


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.


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


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.


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.


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.


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)


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 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 Leakage

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

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.


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.


(crip-toe-spor-ID-ee-OH-sis): The illness produced by infection with <I>Cryptosporidium</I>. 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.


(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.


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.


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.


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).


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.


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.


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.


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.


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.


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.

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Updated on Mon, 22 Jun 2020 by Jonathan

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