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

Specifically, a device or system for the removal of solid particles (suspended solids); in general, includes mechanical, adsorptive, oxidizing and neutralizing filters. (Nonhealth related.)
filter area
The effective area through which water approaches the filter media often expressed in square feet.  Also referred to as surface area.
filter media
(See media.)
filter rating
(See micron rating.)
The effluent liquid which has passed through any style filter.
Extremely small particles of filter media or ion exchange material formed either in the manufacturing process or as a result of breakdown; undesirable in most systems because of high pressure drop.
The agglomeration of finely divided, suspended solids into larger, usually gelatinous, particles; the development of a “floc” after treatment with a coagulant by gentle stirring or mixing.
flow control
A device designed to limit the flow of water or regenerant to a predetermined value over a broad range of inlet water pressures. 
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.
The addition of a fluoride compound to a potable water supply to produce the concentration desired for the reduction in incidence of dental caries.
The process in which undesirable foreign matter accumulates in a bed of filter media or ion exchanger, 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 (CO2) present in water as the gas or as carbonic acid, but not that combined in carbonates or bicarbonates.
free chlorine
(See free available chlorine.)
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 was a linear distance or a percentage of bed depth.