All about Water: Basic Concepts - The Drinking Water - page 16

Chlorine demand —A measure of the amount of chlorine that will
combine with impurities and is therefore unavailable to act as a
disinfectant.
Clean Water Act (CWA) —Federal law dating to 1972 (with several
amendments) with the objective to restore and maintain the chemi-
cal, physical, and biological integrity of the nation's waters. Its long-
range goal is to eliminate the discharge of pollutants into navigable
waters and to make national waters fishable and swimmable.
Coagulants— Chemicals that cause small particles to stick together to
form larger particles.
Coagulation— A chemical water treatment method that causes very
small suspended particles to attract one another and form larger
particles. This is accomplished by the addition of a coagulant that
neutralizes the electrostatic charges that cause particles to repel each
other.
Coliform bacteria— A group of bacteria predominantly inhabiting the
intestines of humans or animals, but also occasionally found else-
where. The presence of these bacteria in water is used as an indi-
cation of fecal contamination (contamination by animal or human
wastes).
Color— A physical characteristic of water. Color is most commonly tan
or brown from oxidized iron, but contaminants may cause other col-
ors, such as green or blue. Color differs from turbidity, which is a
measure of the cloudiness of the water.
Communicable diseases— Usually caused by microbes —microscopic
organisms including bacteria, protozoa, and viruses. Most microbes
are essential components of our environment and do not cause
disease. Those that do are called pathogenic organisms , or simply
pathogens .
Community water system —A public water system that serves at least 15
service connections used by year-round residents or regularly serves
at least 25 year-round residents.
Composite sample —A series of individual or grab samples taken at dif-
ferent times from the same sampling point and mixed together.
Contaminant— A toxic material found as an unwanted residue in or on
a substance.
Cross-connection —Any connection between safe drinking water and a
nonpotable water or fluid.
C × T value— The product of the residual disinfectant concentration ( C ),
in milligrams per liter, and the corresponding disinfectant contact
time ( T ), in minutes. Minimum C × T values are specified by the
Surface Water Treatment Rule as a means of ensuring adequate kill-
ing or inactivation of pathogenic microorganisms in water.