Filter - specifically, a device or system for the removal of solid particles(suspended solids); in general, includes mechanical, adsorptive, oxidizing, and neutralizing filters.
Fixture Unit - an arbitrary unit assigned to different types of plumbing fixtures, and used to estimate flow rate requirements and drain capacity requirements.
Flocculation - 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 of regenerant to a predetermined value over a broad range of inlet water pressures.
Flow Rate - the quantity of water a regenerant which passes a given point in a specified unit of time, often expressed in gallons per minute.
Fluoridation - the addition of a fluoride compound to a water supply to produce the concentration desired for the reduction in incidence of dental carries.
Flush Tank - a tank or chamber in which water is stored for pid release to flush a toilet or water closet.
Flush Valve - a self closing valve designed to release a large volume of water when tripped.
Fouling - 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, htpochlorous acid or hypochlorite, not combined with ammonia or in other less available form.
Freeboard - 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 as a linear distance or a percentage of bed depth.