Glossary of Water Treatment Terms & Definitions - C



Calcium carbonate (CaCO3). A trade name for finely ground limestone, very high in calcium carbonate, which is used to raise the pH of acidic water.

Calcium (Ca)

One of the primary elements of the earth's crust commonly found in water as a dissolved solid. The presence of calcium in water is a factor contributing to the formation of scale and insoluble soap curds which are means of clearly identifying hard water. It is sometimes referred to as lime.

Calcium Carbonate Equivalent

All forms of water hardness and other salts are commonly expressed in terms of calcium carbonate equivalents. This is necessary so that minerals of varying weight can be expressed in chemically equivalent terms.


In a softener or deionizer it is the adsorption activity possessed in varying degree by ion exchange materials. This quality may be expressed as kilograins per cubic foot, gram-milliequivalents per gram, pound-equivalents per pound, gram-milliequivalents per milliliter, etc., where the of these ratios represent the weight of the ions adsorbed and the denominators, the weight or volume of the adsorbent. It can also refer to the ability of any media to take up a specific contaminant and is rated by time over gallons. As to flow rates, it is the maximum or minimum flow obtainable under given conditions of media, temperature, pressure, velocity, etc.

Carbonaceous Exchangers

Ion exchange materials of limited capacity prepared by the sulfonation of coal, lignite, peat, etc.

Carbon Dioxide

Water with a low pH value usually contains free carbon dioxide. Its presence is caused generally by absorption of carbon dioxide (CO2) from the air as water falls as rain, or by decay of organic matter in the earth. Well water containing substantial quantities of CO2 has a resultant low pH and corrosive qualities. Carbon dioxide in water forms a weak carbonic acid.


A substance that can cause cancer.

Cathodic Protection

The control of the electrolytic corrosion of an underground or underwater metallic structure by the application of an electric current is such a way that the structure is made to act as the cathode instead of anode of an electrolytic cell.


A positively charged particle or ion.

Caustic Soda

The common name for sodium hydroxide and often used as a regenerant of anion resin in deionization systems.


The flow of water or regenerant taking the line of least resistance through a media bed, as opposed to the usual distributed flow through all passages of the bed. Channeling may be due to fouling of the bed, poor distribution design, low flow rates, or insufficient backwash.

Chemical Feeder

A mechanical device designed to introduce chemicals into a water system, more or less accurately in proportion to water flow.

Chemical Oxygen Demand (C.O.D.)

The amount of matter, both organic and inorganic, in a water or wastewater which can be oxidized by boiling with a strong oxidizing acid, and expressed as the equivalent amount of oxygen. Often used as a membrane of the strength of sewage.

Chemical Stability

Resistance to chemical change which ion exchange resins must posses despite contact with aggressive solutions.


Chemical complexes formed from the reaction between ammonia and chlorine being used to disinfect many municipal water supplies. Does not combine with organics to form triclomethanes.


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


Widely used in the disinfection of water and as an oxidizing agent for organic matter, iron, hydrogen sulfide, etc. It is available as a gas, as a liquid in sodium, hypochlorite, or as a solid in calcium hypochlorite. In water chlorine reacts with organics to form trihalomethanes (THM) which can cause cancer.

Chlorine Demand

A measure of the amount of chlorine which will be consumed by organic matter in a water before a chlorine residual will be found.


A material such as alum, which will form a gelatinous precipitate in water, and gather finely divided particles into larger ones which can then be removed by settling and/or filtration.


Those regulations which the department having jurisdiction may lawfully adopt.

Coliform Bacteria

A group of organisms primarily found in human and animal intestines and wastes, and thus widely used as indicator organisms to show the presence of such wastes in water and the possible presence of pathogenic (disease producing) bacteria.


Very finely divided solid particles larger than molecules but small enough that they will not settle out of a solution; intermediate between a dissolved particle and a suspended solid which will settle out of solution. Typically between 0.1 and 0.001 microns in diameter, it usually requires coagulation prior to filtration. colloidal (heme) iron may be removed by special anion resin.

Color Throw

Discoloration of the liquid passing through a filtration or ion exchange media. It may be flushing from the media interstices of traces of colored organic reaction intermediates. It could indicate the presence of metallic ions, humus, tannins, or industrial wastes.

Compensated Hardness

A calculated value based on the hardness, the magnesium to calcium ratio, and the sodium concentration of a water. It is used to calculate the reduction in hardness removal capacity of a softener caused by these factors. No single method of calculation has been widely accepted.


Water which has liquefied from steam.


The quality or power to carry electrical current; in water, the conductivity is related to the concentration of ions capable of carrying electrical current. The unit of measure is the mho, which is the reciprocal of resistivity which is the microhm.

Contact Time

The actual time which water remains in contact with an oxidizer, regenerant, or water conditioning media within a water treatment system. The amount of contact time determines the effectiveness of the system. Also called retention time.


The addition of any physical, chemical, biological or radiological substance to water which reduces the value of the water, or interferes with its intended use.

Corporation Cock

A stopcock screwed into the street water main to provide the house service connection.


The destructive disintegration of metals by electromechanical means. Corrosion of iron and steel is commonly called rusting.

Critical Bed Depth

The minimum depth of an adsorbent bed requited to contain the mass transfer zone.

Cross Connection

Any physical connection between two otherwise separated piping systems one of which contains potable water and the other of unknown or questionable safety, whereby flow may occur from one system to the other depending on the pressure differential between the two systems.

Cross Linkage

The bonding of linear polymers into a resinous product with a material such as divenylbenzene (DVB). The degree of crosslinking is a factor of the resin's ability to withstand chemical oxidation. Softening resin is usually 8 percent crosslinked, but can range from 6 percent to 10 percent which is used in hot water applications.


A complete course of ion exchange operation. For instance, a complete cycle of cation exchange would involve: regeneration of the resin, rinse to remove excess regenerant, exhaustion, backwash, and finally regeneration again.


A waterborne protozoan that forms cysts and causes acute illness in humans. This type of organism is resistant to chlorine and ultraviolet light but can be removed by one micron filtration.


Cellulose triacetate. Used to manufacture reverse osmosis membrane.