Fabric Softener

A laundry additive that gives fabrics a soft feel and smooth surface, reduces static electricity and wrinkling, and makes ironing easier. Most fabric softeners are designed for addition to the wash, rinse, or drying cycles.     Wash- and rinse-added types are liquids; dryer-added fabric softeners come as sprays, impregnated tear-off sheets, and impregnated foam (porous) sheets, or as a slow-dispensing solid bar that attaches to the fin of a dryer.     The softening agent most commonly used is a cationic quaternary ammonium compound. A fluorescent whitening agent or bluing is frequently included, as well as fragrance. Infrequently, antimicrobial ingredients are added.     Fabric softening ingredients also are incorporated in some laundry detergent products.


Free Available (residual) Chlorine

Facultative Organisms

Facultative microbes can use either molecular (dissolved) oxygen or oxygen obtained from food material such as sulfate or nitrate ions.  In other words, facultative organisms can live under aerobic or anaerobic conditions.


A temperature scale in which water freezes at 32 degrees and boils at 212 degrees at atmospheric pressure.

Fast Rinse

A rinse process in which the rinse water is applied to the softener bed at the end of brine regeneration at a faster rate of flow than that for which the brine was applied.     Because of the greater density of the brine, it moves down through the bed in a piston-like fashion. If rinsing were to continue at this rate until the chlorides had dropped to the acceptable level at which the unit could be returned to service, the time required would be excessive. After the higher concentrations of brine have passed from the unit, little is gained by prolonging the rinse time.     The rinse rate during the last few minutes is increased approximately fivefold to complete the rinse cycle. This fast rinse quickly removes the last traces of chlorides and significantly reduces the regeneration time.

Fatty Acids

The principal components in the molecular structure of natural fats, vegetable oils, fish oils, waxes, rosin, and essential oils, where they are bound chemically with glycerin; this combination is termed a glyceride.

Fatty Alcohol

Primary alcohols from C<sub>6</sub> to C<sub>22</sub>, usually straight chain, which is the type used by the detergent industry.

Fecal Coliform Bacteria

Bacteria found in the intestinal tracts of mammals and, therefore in, fecal matter. Their presence in water or sludge is an indicator of pollution and possible contamination by pathogens.

Fecal Matter

Matter (feces) containing or derived from animal or human bodily wastes that are discharged through the anus.

Fecal Streptococcus

Streptococcus bacteria found in fecal matter

Feed Pressure

The pressure at which water is supplied to a water treatment device.

Feed Pressure

The pressure at which water is suppled to a water trestment device


An ultrafiltration term borrowed from old-fashioned boiler operators. When applied to an ultrafilter design, it means multiple stages of ultrafilter units where the feedwater is controlled at a rate equal to the permeate plus concentrate flow rates and the reject water from the initial ultrafiltration stages is recirculated to subsequent stages.


The circulating action between a sensor measuring a process variable and the controller which controls or adjusts the process variable.


The water to be treated that is fed into a given water treatment system.


The conversion/breakdown of organic matter by anaerobic bacteria into carbon dioxide, methane, and similar compounds of low-molecular weight.

Ferric Iron

Small solid iron particles containing trivalent iron, usually as gelatinous ferric hydroxide [Fe(OH)<sub>3</sub>] or ferric oxide (Fe<sub>2</sub>O<sub>3</sub>), which are suspended in water and visible as "rusty water." Ferric iron can normally be removed by filtration.     Also called <i>precipitated iron</i>.

Ferrous Iron

A divalent iron ion, usually as ferrous bicarbonate [Fe(HCO<sub>3</sub>)<sub>2</sub>] which, when dissolved in water, produces a clear solution. It is usually removed by cation exchange water softening.     Also called <i>clear water iron</i>.

Ficks Law of Diffusion

A law of chemistry and physics: the rate of diffusion of one substance in another is proportional to the negative gradient of the concentration of the first substance.


See Water Spotting


A device installed as part of the water system through which water flows for the purpose of removing turbidity, taste, color, iron, or odor.     Filters can be loose media beds in tanks or cartridge-type devices (either packed-medium cartridges or membrane cartridges) and filter media may be used for mechanical, adsorptive, neutralizing, or catalyst/oxidation filtration processes.

Filter Aid

An agent (such as diatomite) that improves filtering effectiveness in some way, such as enhancing the retention of particles or increasing the permeability of the filter to water flow.     A filter aid is either added to the suspensions to be filtered or placed on the filter as a layer through which the liquid must pass.

Filter Area

The effective area, expressed in square feet, through which water approaches the filter media.     Also called <i>surface area</i>.

Filter Cake

1. Solids deposited on top of a filter media bed, often by use of chemically feeding a coagulant or filter aid.   2. The dewatered residue from a filter, centrifuge, or other dewatering device.

Filter Media

The selected materials in a filter that form the barrier to the passage of filterable suspended solids or dissolved molecules. Filter media are used to remove undesirable materials, tastes, and odors from a water supply and to adjust the pH in a water supply.     Filter designs include: 1)loose media filters with grains, resin, or other particles lying in beds or loosely packed in column-form in tank-type filters; or 2)cartridge-type filters which may contain membranes, fabric, fiber, bonded-ceramic, precoat, or cast solid-block filter media.   The media used in some filters are chemically inert, such as sand, which performs only a mechanical filtration. Other filter media are multifunctional, chemically-reactive media such as calcite, activated carbon, magnesia, manganese dioxide, and manganese greensand.

Filter Rating

See Micron Rating


The trade name for an aluminum silicate (pumicite) granular product used as a general purpose filter medium.


1. The effluent liquid from a filter system; that part of the feed stream which has passed through the filter.   2. The liquid remaining after removal of solids, as the liquid extracted in the formation of a filter cake.


The process of separating solids from a liquid by means of a porous substance such as a permeable fabric or membrane or layers of inert media.


Extremely small particles which are smaller than the specified size (in millimeters) for the medium. Fines may be formed in the manufacturing process, may result from breakdown of medium particles (ion exchange resins or activated carbon) during service, or may result from the dissolving of a medium such as calcite.     An excess of fines in a filter, softener, or deionizer can create undesirable pressure drop in the system, cause sloughing of particles, or create undesirable qualities in the filter effluent.

Finished Water

Product water as it leaves the municipal treatment plant for delivery to consumers.  When it arrives at the point-of-use, it has become delivered water.  Also called product water.

First Draw

The water that immediately comes out when a tap is first opened. This water is likely to have the highest level of lead contamination from plumbing materials.

First Draw Sample

A one-liter sample of tap water, collected in accordance with CFR Section 141.86(b)(2), that has been standing in plumbing pipes at least six hours and is collected without flushing the tap.


As relates to biology, reproduction by cell division.

Fix, Sample

A sample is fixed in the field by adding chemicals that prevent the water quality indicators of interest in the sample from changing before final measurements are performed later in the lab.

Fixed Bed

1. The filter or ion exchange medium retained in a vessel.   2. Also refers to media beds which are "contained". That is, filled to the top or to the restraining barrier with filter media and not capable of being expanded during backwashing.

Fixed Matter

The residue (particulate and/or dissolved material) that remains behind (immovable or fixed) despite action to expel it, such as the residue remaining after heating or burning a substance to drive off the volatile solids.

Fixed Solids

The term used in the laboratory analysis of the solid's content of water to define the residue of total suspended and/or dissolved solids after ignition (burning) or heating for a specified time at a specified temperature.


As relates to plumbing, any permanently-installed receptacle that will hold water, such as a sink, lavatory, or water closet (toilet).

Fixture Count

A count of the total number of plumbing fixtures (or water outlets) in a building.   A fixture count is determined for the purpose of estimated peak flow rates and sizing equipment, especially for commercial or institutional buildings.


Microorganisms that move by the action of tail-like projections.

Flame Polished

Melted by a flame to smooth out irregularities. Sharp or broken edges of glass (such as the end of a glass tube) are rotated in a flame until the edge melts slightly and becomes smooth.


The portion of a superheated fluid that is converted to vapor when its pressure is reduced as in flash distillation.

Flash Distillation

A distillation process in which hot incoming water flows into a chamber in which pressure is low, causing some of the water to flash (turn quickly into steam.)


As relates to water treatment, avery fine, fluffy-type mass formed by the coming together of a number of fine suspended particles. A floc can occur naturally, but most frequently it is induced by the addition of a coagulant/flocculent to raw water which contains undesirable turbidity or color.     In wastewater treatment, a clump of solids formed in sewage by biological or chemical action.


A very fine, fluffy-type mass formed by the coming together of a number of fine suspended particles.  A floc can occur naturally, but most frequesntly it is induced by the addition of a coagulant/flocculent to raw water which contains undesirable turbidity of color.

Floc (waste water treatment)

A clump of solids formed in sewage by biological or chemical action.

Floc (Water Treatment)

A very fine, fluffy-type mass formed by the coming together of a number of fine suspended particles.  A floc can occur naturally, but most frequesntly it is induced by the addition of a coagulant/flocculent to raw water which contains undesirable turbidity of color.


The process of bringing together destabilized or coagulated particles to form larger masses or flocs (usually gelatinous in nature) which can be settled and/or filtered out of the water being treated.


Materials which when added to water cause suspended particles to coagulate into larger groupings and form gelatinous clouds of precipitate which enclose additional fine particles of suspended dirt.     The precipitate and the dirt can then be settled or filtered out of the water being treated.

Flood Plain

The flat or nearly flat land on the floor of a stream valley or tidal area that is covered by water during floods.

Flood Rim

The edge of a receptacle (such as a plumbing fixture) from which water will overflow.

Flow Control Valve

A cylindrical pressure-compensating valve installed to regulate the flow of water.  Rated in gpm or gpd.

Flow Controller

An in-line device or orifice fitting which will regulate and control flow of water or regenerant over a broad range of inlet water pressures. Some types are manually adjustable.

Flow Meter

An instrument, mechanical or electronic, used for recording (in gallons, cubic feet, or cubic meters) the quantity of water passing through a particular pipe line or outlet.     In water processing systems, meters may initiate certain functions such as automatically starting the regeneration cycle in an ion exchange system.

Flow Rate

The quantity of water or regenerant which passes a given point in a specified unit of time, often expressed in U.S. gpm (or L/min).     In filters, flow rate is usually measured in gpm/sq.ft. of bed area. In ion exchangers, it is expressed in gpm/cu.ft. of resin.     Flow rate is a critical design parameter by which the effectiveness of the water treatment unit is measured.

Flow Sensor

A device that measures flow rate and can control or measure an action (such as chemical feed) in proportion to the flow rate of the fluid.

Flow Switch

A device which, according to a preset flow rate condition, causes an action when the actual flow rate falls outside the preset limit(s).


A mass of solid particles that is made to flow like a liquid by injection of water or gas is said to have been fluidized.     In water treatment, a bed of filter media is fluidized by backwashing water through the filter.

Fluidized Bed

A medium bed which has become expanded during the backwash step or during "upflow" regeneration of an ion exchanger.


A raceway or channel constructed to carry water or to permit the measuring of its flow.


An orange-red compound that exhibits intense fluorescence in alkaline solutions and is used to dye water in order to trace its course and movement.


The addition of a chemical to increase the concentration of fluoride ions in drinking water to a predetermined optimum limit to reduce the incidence (number) of dental caries (tooth decay) in children.     Defluoridation is the removal of excess fluoride in drinking water to prevent the mottling (brown stains) of teeth.


A naturally-occurring constituent of some water supplies, an excess of which (over 2.0 ppm) can cause discolored teeth (mottling).     Skeletal fluorosis, a serious crippling bone disorder resembling osteoporosis, can develop from many years of exposure to drinking water with more than 4.0 ppm of fluoride.


An abnormal condition caused by excessive intake of fluorine, characterized chiefly by mottling of the teeth.


1. To open a cold-water tap to clear out all the water which may have been sitting for a long time in the pipes. In new homes, to flush a system means to send large volumes of water gushing through the unused pipes to remove loose particles of solder and flux.  <p>  2. To force a cleansing liquid rapidly through piping, tubing, storage vessels, process tanks, or other plumbing items to clean them out.

Flush Tank

The chamber of the toilet in which the water is stored for rapid release to flush the toilet. The size of the flush tank is to be accounted for in proper sizing of any plumbing system or water treatment system.

Flush Valve (Flushometer)

A self-closing valve used for flushing urinals and toilets in public buildings.   This type of valve allows very high flow rates (15-20 gpm) for a few seconds.


In municipal water systems, a method used to clean water distribution lines. Hydrants are opened and water with a high velocity flows through the pipes, removes deposits from pipes, and flows out the hydrants.


In cross flow filtration, the flow rate of product water through a reverse osmosis, electrodialysis, or ultrafiltration membrane.     The flow rate is usually given in terms of volume unit per time per membrane area, such as gallons per day per square foot or liters per hour per square meter.

Fluxing Lime

See Lime (CaO)


The trade name for a patented medium composed of high purity copper and zinc granules.     KDF is capable of removing chlorine, soluble heavy metals, and other inorganic contaminants from water through the chemical reduction/oxidation (redox) process.


Free mineral acidity


A mass of bubbles formed on liquids by agitation.

Foot Valve

A water softener valve, controlled by a float, which controls the amount of water entering or brine solution leaving the brine tank. A special type of check valve located at the bottom end of the suction pipe on a pump. This valve opens when the pump operates to allow water to enter the suction pipe but closes when the pump shuts off to prevent water from flowing out of the suction pipe.

Forced-Draft Degasifier

A tall column wherein water is sprayed downward through an upward flow of air for the purpose of removing gases such as carbon dioxide after the decationization unit in a deionization plant.


Formic aldehyde methanol, HCHO<sub>3</sub>, made by oxidation of synthetic methanol or low-boiling petroleum gases such as propane or butane. Available commercially as a 37-50 percent aqueous solution which may contain up to 15 percent methanol to inhibit polymerization.     Commercial grades are called formalin. An effective preservative, disinfectant, and sanitizing agent, although it is not a sterilizer, because formaldehyde does not kill completely all microorganisms. Is not typically used to sanitize drinking water treatment equipment because of personal hazards associated with it i.e., toxic by inhalation, strong irritant, and a carcinogen.


Commercial grades of formaldehyde.


A group of similar consolidation (that is, relatively solid) rocks of unconsolidated (that is, relatively loose) minerals.


In electrodialysis applications, the deposit of organic or other materials on the surface of the electrodialysis membrane surface, causing membrane inefficiencies.     As relates to filtration or ion exchange, the accumulation of undesirable foreign matter in a filter or ion exchange media bed causing clogging of pores or coating of surfaces and inhibiting or limiting the proper operation of the bed and the treatment system.     In reverse osmosis or ultrafiltration applications. a phenomenon in which a reverse osmosis or ultrafiltration membrane adsorbs, interacts with, or becomes coated by solutes and/or precipitates in the feed stream resulting in a decrease in membrane performance by lowering the flux and/or affecting the rejection of solutes.

Fouling (electrodialysis)

The deposit of organic or other materials on the surface of the electrodialysis membrane, causing membrane inefficiencies.

Fouling (filtration/ion exchange)

The accumulation of undesirable foreign matter in a filter or ion exchange media bed causing clogging of pores or coating of surfaces and inhibiting or limiting the proper operation of the bed and the treatment system.

Fouling (reverse osmosis/ultrafiltration)

A phenomenon in which a reverse osmosis or ultrafiltration membrane absorbs, interacts with, or becomes coated by solutes and/or precipitates in the feed stream resulting in a decrease in membrane performance by lowering the flux and/or affecting the rejection of solutes.


Feet (foot) per second


To separate into fractions or parts.

Free Acid Form

The regenerated form of a weak acid cation exchanger.

Free Available (Residual) Chlorine (FAC)

That portion of the total available residual chlorine composed of dissolved chlorine gas (Cl<sub>2</sub>), hypochlorous acid (HOCl), and/or hypochlorite ion (OCl<sup>-</sup>) remaining in water after chlorination.     This does not include chlorine that has combined with ammonia, nitrogen, or other compounds.

Free Base Form

The regenerated form of a weak basic anion exchanger.

Free Carbon Dioxide

Carbon dioxide present in water as gas or as carbonic acid but not including that carbon dioxide in combination as in carbonates or bicarbonates.

Free Mineral Acidity

Acidity in water due to the presence of strong inorganic acids like hydrochloric, nitric, and sulfuric acids, as opposed to weak acidity due to such acids as carbonic or acetic. Mineral acidity is usually expressed in water analysis as FMA.

Free Residual Chlorination

The application of chlorine to water to produce a free available chlorine residual equal to at least 80 percent of the total residual chlorine (sum of free and combined available chlorine residual).


The vertical distance between the top of a filter media bed (or ion exchange resin bed) and the overflow or collector. This space allows for bed expansion during backwashing.     The distance may be expressed in linear measurement or as a percent of the bed depth.

Fresh Water

Water having less than approximately 1,000 mg/L (ppm) of total dissolved solids (TDS).


An expression of the ability of ion exchange beads to resist cracking under hydrostatic operation.

Friction Losses

The head, pressure, or energy (they are the same) lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water and the roughness of the pipe, channel walls, and restrictions caused by fittings.     Water flowing in a pipe loses pressure or energy as a result of friction losses.

Fullers Earth

A clayish substance of hydrous aluminum silicate used as a filter aid in coagulation.

Fulvic Acid

A water-soluble, natural organic substance of low molecular weight which is derived from humus often found in surface water.     Fulvic acid contributes to the formation of trihalomethanes in chlorinated water supplies and can contribute to organic fouling of ion exchange resin beds. Fulvic acids are chelating agents that can bind and hold metal ions in solution, and are particularily involved in the solubilization and transport of iron in water.     Fulvic acid compounds are associated with color in water. These yellow-brown materials frequently are encountered along with soluble iron.

Functional Groups

See Exchange Sites


<i>(singular = fungus)</i> Mushrooms, molds, mildews, rusts, and smuts that are small nonchlorophyll-bearing plantlike organisms lacking roots, stems, and leaves. They have distinct nuclei surrounded by nuclear membranes as well as other specialized functional cell parts but cannot carry on photosynthesis. They occur in natural waters and grow best in the absence of light.     Their decomposition may cause objectionable tastes and odors in water.

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Updated on Mon, 22 Jun 2020 by Jonathan

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