Learn about the different types of contaminants that might put your family at risk.

One of the principal elements (Ca) making up the earth’s crust, the compounds of which when dissolved make the 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 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 (CLO)24H2O], used as a bleach and a source of chlorine in water treatment.  Specifically useful because it is stable as a dry powder and can be formed into tablets. 
An expression of the quantity of an undesirable material which can be removed by a water conditioner between servicing of the media, 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 removal 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. 
carbon dioxide
A gas (CO2) present in the atmosphere and formed by the decay of organic matter; the gas in carbonated beverages; in water, it forms carbonic acid.    
The CO3 ion.
carbonate alkalinity
Alkalinity (CO3) due to the presence of the carbonate ion. 
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. 
A material substance that induces excessive or abnormal cellular growth cancer in an organism. 
Any removable, preformed, or prepackaged component containing a filtering media or ion exchanger.  Also referred to as “element”.
A substance that increases the rate or yield of a chemical reaction without being consumed itself.
catalyzed oxidation
Enhancement of chemical or biological oxidation by the addition of catalytic agents that promote higher rates of reaction. 
The negative pole of an electrolytic system; an electrode where reduction occurs.
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. 
An ion with a positive electrical charge, such as calcium, magnesium, sodium, iron, lead, and manganese. 
cation exchange
Ion exchange process in which cations in solution are exchanged for other cations from an ion exchanger. 
cationic flocculant
A polyelectrolyte with a net positive electrical charge. 
Any substance capable of burning or destroying animal flesh or tissue.  The term is usually applied to strong bases such as lye. 
caustic soda
The common name for sodium hydroxide, (NaOH).
The flow of water or other solution in 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. 
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. 
chemical feeder
A mechanical device designed to introduce chemicals into a water system, more or less accurately in proportion to water flow. 
A combination of chlorine and a small amount of ammonia, chloramine is a disinfectant used by some water utilities. The addition of the ammonia helps to make the solution more stable and longer lasting. Chloramines can cause an adverse effect on the taste and odor of water.
A mechanical device specifically designed to feed chlorine gas or solutions of its compounds, such as hypochlorites, into a water supply in proportion to the flow of water. 
A gas used by many water utilities for the disinfection of water and as an oxidizing agent for organic matter and some metals. It imparts a noticeable taste and odor to water, and may contribute to the formation of trihalomethanes (THM).
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; the difference between the total chlorine fed and the chlorine residual. 
The removal of small quantities (<2%) of fine particulate matter (solids) from a liquid (water) to improve the product liquid.  Generally, clarifiers will remove particles from 2 to 100 micrometers in size.  Clarification methods include filtration, gravity and centrifugal sedimentation, and magnetic separation. 
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 larger or heavier particles, speeding the reactions, or by permitting reduced coagulant dosage. 
The process in which very small, finely divided solid particles, often colloidal in nature, are agglomerated into larger particles.
co-current flow
(See downflow.)
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. 
Very finely divided solid particles which will 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 to form larger particles which may be removed by sedimentation and/or filtration.
The shade or tint imparted to water by substances in true solution, and thus not removed by mechanical filtration; most commonly caused by dissolved mineral matter.
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 vessel containing a bed of filter media or ion exchange; may be either upflow or downflow. 
combined available chlorine
The chlorine present as chloramines or other derivatives in a water, but still available for disinfection and the oxidation of organic matter.  The combined chlorine compounds are more stable than free chlorine forms, but are somewhat slower in action. 
composite sample
A mixture of a number of single or “grab” samples intended to produce a typical or average sample when wide variations in quality or characteristics may occur; may be made up of equal volumes of individual samples or of single samples proportioned to variations in flow or usage. 
The addition of foreign matter to a substance which reduces the value of the substance or interferes with its intended use.
In physics, mass motions within a fluid resulting in transport and mixing of the properties of that fluid caused by the force of gravity and by differences in density due to nonuniform temperature. 
The destructive disintegration of a metal by electrochemical means.
countercurrent flow
(See upflow)
cross connection
A direct link between a potable water system and a non potable water system which would permit 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).
A slang expression sometimes used to mean a cubic foot of ion exchanger or filter media.
cubic foot
The common basis for the measurement of the volume of ion exchangers or loose filter media.  The measurement is made after a specific process including backwashing and settling of the bed and draining excess water from above the bed.  A cubic foot equals 28.3 liters.
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; sometimes incorrectly used in reference to a single step of a complete cycle.
(See spore.)