Additional Information 

Absolute Filter Rating

Filter rating meaning that 99.9 % (or essentially all) of the particles larger than a specified micron rating will be trapped on or within the filter.


The process in which one substance penetrates into the body of another substance, termed the absorbent. An example is the absorption of water into soil.


A substance which releases hydrogen ions when dissolved in water. Most acids will dissolve the common metals and will react with a base to form a neutral salt and water. An acid is the opposite of an alkali, has a pH rating lower than 7.0, will turn litmus paper red, and has a sour taste.


The quantitative capacity of a water or water solution to neutralize an alkali or base. It is usually measured by titration with a standard solution of sodium hydroxide, and expressed in ppm or mg/L of its calcium carbonate equivalent.

Activated Alumina

A medium made by treating aluminum ore so that it becomes porous and highly adsorptive. Activated alumina will remove several contaminants including fluoride, arsenic, and selenium. It requires periodic cleaning with a regenerant such as alum, acid and/or caustic.

Activated Carbon

A water treatment medium, found in block, granulated, or powdered form, which is produced by heating carbonaceous materials, such as coal, wood, or coconut shells, in the absence of air, creating a highly porous adsorbent material. Activated carbon is commonly used for dechlorination, organic chemical reduction and radon reduction, and is recognized by the US EPA as the best available technology for reduction of organic chemicals from drinking water.

Activated Silica

A negatively charged colloidal substance generally formed by combining a dilute sodium silicate solution with a dilute acidic solution (or other activant). Generally used as a coagulant aid.


Any substance that is or can be adsorbed. The liquid, gas or solid substance which is adsorbed as molecules, atoms, or ions.


A water treatment medium, usually solid, capable of the adsorption of liquids, gases, and/or suspended matter. Activated alumina and activated carbon are common adsorbents used in water processing.


The physical process occurring when liquids, gases, or suspended matters adhere to the surfaces of, or in the pores of, an adsorbent media such as activated carbon. Adsorption is a physical process which occurs without chemical reaction.


The process in which air is brought into intimate contact with water, often by spraying water through air, or by bubbling air through water. Aeration may be used to add oxygen to the water for the oxidation of matter such as iron, or to cause the release of dissolved gases such as carbon dioxide or hydrogen sulfide from the water.


An action or process conducted in the presence of air, such as aerobic digestion of organic matter by bacteria.

Air Check

A device which allows water, but not air, to pass through it. An air check is a typical component of a treatment system using a regenerant eductor.

Air Gap

A clear vertical space through the free atmosphere between the lowest opening of any pipe or faucet conveying water or waste to a tank, plumbing fixture receptor, or other device and the flood level rim of the receptacle. An air gap is used to prevent cross connection between a water treatment device and a possible source of wastewater thereby preventing a reverse flow of water from the sewer into the water supply system. Without an air gap, such reverse flow could occur due to an increase in the pressure in the sewer system or the creation of a negative pressure in the water supply line. Local plumbing codes usually require the air gap to be twice the diameter of the inlet with a minimum width of 1 1/2 inches.

Aggressive Water

A term usually applied to waters containing acid or oxygen which hasten corrosion (rusting).


Plant life (green scum) containing chlorophyll is usually found in stagnant surface water. Excessive growths may create taste and odor problems, and consume dissolved oxygen during decay. Sometimes it may be controlled in a pond by the addition of Potassium Permanganate. In a water supply system, chlorination followed by dechlorination is often used.


A substance which creates a bitter taste and a slippery feel when dissolved in water and will turn red litmus paper blue. An alkali has a pH greater than seven and is the opposite of an acid. Highly alkaline waters tend to cause drying of the skin.
Alkalis may include the soluble hydroxide, carbonate, and bicarbonate salts of calcium, magnesium, potassium, and sodium. A hydroxide alkali may also be called a base.


The quantitative capacity of water to neutralize an acid; that is, the measure of how much acid can be added to a liquid without causing a significant change in pH. Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have high alkalinity. In the water industry, alkalinity is expressed in mg/l of equivalent calcium carbonate. There are three kinds of alkalinity: carbonate, bicarbonate, and hydroxide alkalinity. Total alkalinity is the sum of all three kinds of alkalinity. Different tests are used to determine the quantity of the different kinds of alkalinities present in water.

Alternating System

As in the pressure in the sewer system or the creation of a negative pressure in the water supply line. Local plumbing codes usually require the air gap to be twice the diameter of the inlet with a minimum width of 1 1/2 inches.


The common name for aluminum sulfate [Al2 (SO4) x 14H2 O] which is often used as a coagulant in water treatment.


A single celled protozoan that is widely found in fresh and salt water. Some types of amoebas cause diseases such as amoebic dysentery.

Anaerobic organism

An organism that can thrive in the absence of oxygen (air), such as bacteria in a septic tank.

Angstrom unit

A unit of wavelength of light equal to .00001 millimeter or .0001 microns.


A negatively charged ion in solution, such as bicarbonate, chloride, or sulfate. An anion [such as chloride (Cl-)] may result from the dissociation of a salt, acid, or alkali.

Anion Exchange

An ion exchange process in which anions in solution are exchanged for other anions from an ion exchanger. In demineralization, for example, bicarbonate, chloride and sulfate anions are removed from solution in exchange for a chemically equivalent number of hydroxide anions from the anion exchange resin.


The positive pole of an electrolytic system. The metal which goes into solution in a galvanic cell. Anodes of metals such as magnesium and zinc are sometimes installed in water heaters or other tanks to deliberately establish galvanic cells to control corrosion of the tank through the sacrifice of the anode.


Abbreviation for American National Standards Institute.


Containing water; watery.


Natural underground reservoirs of porous layers of sand, rock or gravel.


Describes underground water trapped under pressure between layers of impermeable rock. An artesian well is one that taps artesian water.


Abbreviation for American Society of Mechanical Engineers.


The process in which solids are worn down by friction, often between particles of the same material. Filter media and ion exchange materials are subject to attrition during backwashing, regeneration and service.

Automatic water softener (or Automatic Filter)

A water softener (or filter) that is equipped with a clock timer, meter, or sensor which automatically initiates the backwash and/or regeneration process at the preset intervals of time. A predetermined number of gallons of water usage or as determined by a sensor. All operations, including bypass of treated or untreated water (depending upon design), backwashing, brining, rinsing, and returning the unit to service are performed automatically.


Abbreviation for American Water Works Association. Most municipal water treatment plants hold membership in this association.

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Flow of water in a pipe or line in a direction opposite to the normal flow; often associated with back siphonage or the flow of possibly contaminated water into a potable water system.

Backflow Preventor

A device or system installed in a water line to stop backflow from a non-potable source.

Back Pressure

Pressure which creates resistance against the flow of water.


The upflow or counter-current flow of water through a filter or ion-exchange medium, lifting the mineral bed and flushing away to the drain the particles of foreign matter that have been filtered from the water supply during the service cycle.


Unicellular microorganisms which typically reproduce by cell division. Although usually classed as plants, bacteria contain no chlorophyll. Many different types of bacterial organisms are often found in drinking water. Most municipally treated water is essentially bacteria free due to the addition of chlorine. Some forms of cyst type viruses have a degree of immunity to chlorine due to the cocoon-like shell around the virus. These types of organisms such as Giardia Cyst, Giardia Lamblia, and Cryptosporidium have a physical size of three to seven microns and can be effectively removed by sub-micron filtration. Some bacteria are helpful to man, others harmful.


Having the ability to inhibit the growth of bacteria without destroying them. For example, silver impregnated activated carbon will limit bacterial colonization but not eliminate it.


Any substance or agent which kills bacteria.


A unit of pressure. One bar equals 14.5 pounds per square inch (psi) or about 0.987 standard atmospheres.


An alkali that releases hydroxyl ions when dissolved in water. Bases reset with acids to form a neutral salt and water. In general they taste bitter rather than sour, and feel slippery and reverse the color changes produced by acids in indicators. For example, they turn litmus paper blue.

Batch Operation

The utilization of ion exchange resins to treat a solution in a container wherein the removal of ions is accomplished by agitation of the solution and subsequent decanting of the treated liquid.


A mass of ion exchange resin particles or filter media contained in a column.

Bed Depth

The height of the resin or filter media in the column after it has been properly conditioned for effective operation, usually expressed in inches. This depth excludes any supporting bed.

Bed Expansion

The effect produced during backwashing: the resin particles become separated and rise in the column. The expansion of the bed due to the increase of the space between resin particles may be controlled by regulating backwash flow.

Bicarbonate Alkalinity

The presence in a solution of hydroxyl (OH-) ions resulting from the hydrolysis of carbonates or bicarbonates. When these salts react with water, a strong base and a weak acid are procured, and the solution is alkaline.


A chemical which can kill or inhibit the growth of lining organisms such as bacteria, fungi, molds, and slime. Biocides can be harmful to humans.


Subject to degradation into similar substances by biological action . Examples include detergents, sewage, and other organic matter by bacteria.


The trade name for a manganese dioxide coated aluminum silicate used as an oxidizing catalyst filter medium for iron and manganese reduction.


The withdrawal of water containing a high concentration of solids or dissolved solids or maintain a specified solids-to-water concentration ratio.


Abbreviation for Biochemical Oxygen Demand. The amount of oxygen consumed in the oxidation of organic matter by biological action under specific standard test conditions. Widely uses as a measure of the strength of sewage and wastewater.

Bone Char

A black pigment substance with a carbon content of about 10 percent, made by carbonizing animal bones. It is used as a selective anion exchanger for fluoride and arsenic reduction.

Brackish Water

Water containing bacteria between 1.000 and 15,000 ppm of dissolved solids.


The first appearance in the solution flowing from an ion exchange unit of unabsorbed ions similar to those which are depleting the activity of the resin bed. Breakthrough is an indication that regeneration of the resin is necessary.


A strong solution of salt(s), such as the sodium chloride or potassium brine used in the regeneration of ion exchange water softeners, but also applied to the mixed sodium, calcium and magnesium chloride waste solution from regeneration.

Brine Ejector (Eductor)

A device used to draw a solution such as brine from a storage tank and force it into a cation or anion water treatment unit.

Brine Tank

A tank which sits beside the softening unit and acts as a salt storage and brine supply.


A chemical which causes a solution to resist changes in pH, or to shift the pH to a specific value.


A connection or a valve system that allows untreated water to flow to a water system while a softener or filter is being regenerated, backwashed or serviced; also applied to a special water line installed to provide untreated water to a particular tap, such as a sill cock.

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Calcium carbonate (CaCO3). A trade name for finely ground limestone, very high in calcium carbonate, which is used to raise the pH of acidic water.

Calcium (Ca)

One of the primary elements of the earth's crust commonly found in water as a dissolved solid. The presence of calcium in water is a factor contributing to the formation of scale and insoluble soap curds which are means of clearly identifying hard water. It is sometimes referred to as lime.

Calcium Carbonate Equivalent

All forms of water hardness and other salts are commonly expressed in terms of calcium carbonate equivalents. This is necessary so that minerals of varying weight can be expressed in chemically equivalent terms.


In a softener or deionizer it is the adsorption activity possessed in varying degree by ion exchange materials. This quality may be expressed as kilograins per cubic foot, gram-milliequivalents per gram, pound-equivalents per pound, gram-milliequivalents per milliliter, etc., where the of these ratios represent the weight of the ions adsorbed and the denominators, the weight or volume of the adsorbent. It can also refer to the ability of any media to take up a specific contaminant and is rated by time over gallons. As to flow rates, it is the maximum or minimum flow obtainable under given conditions of media, temperature, pressure, velocity, etc.

Carbonaceous Exchangers

Ion exchange materials of limited capacity prepared by the sulfonation of coal, lignite, peat, etc.

Carbon Dioxide

Water with a low pH value usually contains free carbon dioxide. Its presence is caused generally by absorption of carbon dioxide (CO2) from the air as water falls as rain, or by decay of organic matter in the earth. Well water containing substantial quantities of CO2 has a resultant low pH and corrosive qualities. Carbon dioxide in water forms a weak carbonic acid.


A substance that can cause cancer.

Cathodic Protection

The control of the electrolytic corrosion of an underground or underwater metallic structure by the application of an electric current is such a way that the structure is made to act as the cathode instead of anode of an electrolytic cell.


A positively charged particle or ion.

Caustic Soda

The common name for sodium hydroxide and often used as a regenerant of anion resin in deionization systems.


The flow of water or regenerant taking the line of least resistance through a media bed, as opposed to the usual distributed flow through all passages of the bed. Channeling may be due to fouling of the bed, poor distribution design, low flow rates, or insufficient backwash.

Chemical Feeder

A mechanical device designed to introduce chemicals into a water system, more or less accurately in proportion to water flow.

Chemical Oxygen Demand (C.O.D.)

The amount of matter, both organic and inorganic, in a water or wastewater which can be oxidized by boiling with a strong oxidizing acid, and expressed as the equivalent amount of oxygen. Often used as a membrane of the strength of sewage.

Chemical Stability

Resistance to chemical change which ion exchange resins must posses despite contact with aggressive solutions.


Chemical complexes formed from the reaction between ammonia and chlorine being used to disinfect many municipal water supplies. Does not combine with organics to form triclomethanes.


A mechanical device specifically designed to feed chlorine gas or pellets, or solutions such as hypochlorides, into a water supply in proportion to the flow of water.


Widely used in the disinfection of water and as an oxidizing agent for organic matter, iron, hydrogen sulfide, etc. It is available as a gas, as a liquid in sodium, hypochlorite, or as a solid in calcium hypochlorite. In water chlorine reacts with organics to form trihalomethanes (THM) which can cause cancer.

Chlorine Demand

A measure of the amount of chlorine which will be consumed by organic matter in a water before a chlorine residual will be found.


A material such as alum, which will form a gelatinous precipitate in water, and gather finely divided particles into larger ones which can then be removed by settling and/or filtration.


Those regulations which the department having jurisdiction may lawfully adopt.

Coliform Bacteria

A group of organisms primarily found in human and animal intestines and wastes, and thus widely used as indicator organisms to show the presence of such wastes in water and the possible presence of pathogenic (disease producing) bacteria.


Very finely divided solid particles larger than molecules but small enough that they will not settle out of a solution; intermediate between a dissolved particle and a suspended solid which will settle out of solution. Typically between 0.1 and 0.001 microns in diameter, it usually requires coagulation prior to filtration. colloidal (heme) iron may be removed by special anion resin.

Color Throw

Discoloration of the liquid passing through a filtration or ion exchange media. It may be flushing from the media interstices of traces of colored organic reaction intermediates. It could indicate the presence of metallic ions, humus, tannins, or industrial wastes.

Compensated Hardness

A calculated value based on the hardness, the magnesium to calcium ratio, and the sodium concentration of a water. It is used to calculate the reduction in hardness removal capacity of a softener caused by these factors. No single method of calculation has been widely accepted.


Water which has liquefied from steam.


The quality or power to carry electrical current; in water, the conductivity is related to the concentration of ions capable of carrying electrical current. The unit of measure is the mho, which is the reciprocal of resistivity which is the microhm.

Contact Time

The actual time which water remains in contact with an oxidizer, regenerant, or water conditioning media within a water treatment system. The amount of contact time determines the effectiveness of the system. Also called retention time.


The addition of any physical, chemical, biological or radiological substance to water which reduces the value of the water, or interferes with its intended use.

Corporation Cock

A stopcock screwed into the street water main to provide the house service connection.


The destructive disintegration of metals by electromechanical means. Corrosion of iron and steel is commonly called rusting.

Critical Bed Depth

The minimum depth of an adsorbent bed requited to contain the mass transfer zone.

Cross Connection

Any physical connection between two otherwise separated piping systems one of which contains potable water and the other of unknown or questionable safety, whereby flow may occur from one system to the other depending on the pressure differential between the two systems.

Cross Linkage

The bonding of linear polymers into a resinous product with a material such as divenylbenzene (DVB). The degree of crosslinking is a factor of the resin's ability to withstand chemical oxidation. Softening resin is usually 8 percent crosslinked, but can range from 6 percent to 10 percent which is used in hot water applications.


A complete course of ion exchange operation. For instance, a complete cycle of cation exchange would involve: regeneration of the resin, rinse to remove excess regenerant, exhaustion, backwash, and finally regeneration again.


A waterborne protozoan that forms cysts and causes acute illness in humans. This type of organism is resistant to chlorine and ultraviolet light but can be removed by one micron filtration.


Cellulose triacetate. Used to manufacture reverse osmosis membranes.



A process for the reduction of alkalinity in a water supply. It is generally accomplished by a chemical feed processor combined cation and anion exchange systems.


The removal from solution of inorganic salts by means of adsorption by ion exchange resins of both the cations and the anions that comprise the salts.


The removal of excess or free chlorine from a water supply by adsorption with activated carbon or by catalytic type filter media.


The degradation of an ion exchange resin structure by destruction of the crosslink polymer as the result of aggressive attack by chlorine, ozone, hydrogen peroxide, or heat. Decrosslinking causes increased moisture content in an ion exchange resin and the physical swelling of the beads.


The removal of dissolved gasses from water such as carbon dioxide, methane, hydrogen sulfide, and oxygen. This can by done by subjecting the water to below atmospheric pressure, or by passing air through the water at atmospheric pressure.


The removal of the ionized minerals and salts (both organic and inorganic) from a solution by a two-phase ion exchange procedure. First, positively charged ions are removed by a cation exchange resin in exchange for a chemically equivalent amount of hydrogen ions. Second, negatively charged ions are removed by an anion exchange resin for a chemically equivalent amount of hydroxide ions. The hydrogen and hydroxide ions introduced in this process unite to form water molecules. The term is often used interchangeably with demineralization. The cation resin is regenerated with an acid and the anion resin is regenerated with sodium hydroxide (caustic soda).

Delta P

The pressure drop or loss in psi between the inlet and the outlet of a water conditioner as the water flows.

Density, Apparent (Density, Bulk)

The mass under specified conditions of a unit volume of a solid sorbent including its pore volume and inter-particle voids.


The removal of dissolved inorganic solids (salts) from a solution such as water to make it free of dissolved salts. Typically accomplished by reverse osmosis, distillation, or electrodialysis.


Usually refers to synthetic detergent, but can be any material with cleansing powers such as soap, alkaline materials, synthetic detergents, solvents, and abrasives. Synthetic detergents are known as surfactants which foam and act like soap but are not made from fatty acids and lye.


The separation of components of a solution by diffusion through a semi-permeable membrane which is capable of passing certain ions or molecules while rejecting others.


A carbonate mineral of calcium and magnesium found in nature in extensive beds of compact limestone and marble that are rich in carbonate.

Drain Line

A pipe or conduit from a water conditioning unit used to carry backwash water, regeneration wastes and/or rinse water to a drain or waste system by gravity.

Drinking Water Standards

National Primary Drinking Water Standards are established by the U.S. Environmental Protection Agency (EPA) are health related and establish the maximum contaminant levels (MCL's) for regulated substances in drinking water. A MCL is the highest permissible level of a contaminant allowed in water delivered to the consumer's tap. These standards relate to public water systems. National Secondary Drinking Water Standards are also issued by the EPA and pertain to aesthetic characteristics of water and are recommended only. Drinking Water Standards


Abbreviation for Drainage, Waste, and Vent. A name for copper or plastic tubing used for drain, waste, or venting pipes.

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A venturi with an opening at the throat used to educt (suck in) air or liquid. The common method of introducing brine into a water softener.


The effectiveness of the operational performance of an ion exchanger. Efficiency in the adsorption of ions is expressed as the quantity of regenerant required to effect the removal of a specified unit weight of adsorbed material, e.g., pounds of acid per kilogram of salt removed.


The outflow of a water treatment device. Sometimes used to mean the product water of a given water conditioning device or system.


A dialysis process using semi-permeable membranes.


A chemical compound which dissociates or ionizes in water to produce a solution which will conduct an electric current. Could be an acid, base, or salt.


The stripping of adsorbed ions from an ion exchange material by the use of solutions containing other ions in concentrations higher than those of the ions to be stripped. The process of washing out adsorbed material, especially by use of a solvent.


The end point is that point in the exhaustion run of a water conditioner such as a softener or deionizer at which the water quality has dropped below an acceptable level


The aging process of a body of water caused by the depletion of available oxygen. It can be accelerated by human activities that add too many nutrients to the water such as barn yard runoff or fertilizers.

Exchange Sites

Locations on ion exchange resin beads which hold mobile ions that are available for exchange with other ions in a solution passing through the bed. These sites are also called functional groups.

Exchange Velocity

The rate with which one ion is displaced from an exchanger in favor of another.


The state of the adsorbent such as activated carbon, a water softener, or a deionizer that is no longer capable of the removal of a specific pollutant or of useful ion exchange. The exhaustion point is determined arbitrarily in terms of: (a) the presence or increase of an adsorbent contaminant as chlorine; (b) a value in parts per million of ions in the effluent solution; (c) the reduction in quality of the effluent water determined by a conductivity bridge which measures the resistance of the water to the flow of an electric current.

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Ferric Iron

Small solid iron particles containing trivalent iron, usually as gelatinous ferric hydroxide or ferric oxide (Fe2O3), which are suspended in water and visible as "rusty" water. Ferrous (iron in solution) is readily converted to ferric iron by exposure to oxygen found both in water and air. Ferric iron can by removed by filtration, but not by ion-exchange.

Ferrous Iron

Usually ferrous hydroxide which when dissolved in water produces a clear solution. Often called clear water iron, it can be removed by ion-exchange.


A naturally occurring ore which serves as a catalytic filter media in the removal of iron, hydrogen sulfide and manganese. It normally requires only backwashing, but the use of oxidizers such as chlorine or potassium permanganate enhances its action.


A device used to clean water by removing iron, silt, taste, odor, color, etc., before it is fed into the softener or supply lines of the consumer. Includes mechanical, adsorptive, oxidizing and neutralizing filters. Available as media beds in tanks or as cartridge type devices


The tradename for aluminum silicate (pumicite) granular product used as a general purpose filter medium. Lighter in weight, it requires a lower backwash rate. Typically removed suspended solids down to the 20-40 micron range.


The process of passing water through a porous substance to remove solids in suspension. Available as media beds in tanks or as cartridge type devices


Smaller than the specified size or particles of ion exchange or filtration materials. An excess of fines can create undesirable pressure drop in the system.

Fixture Count

A count of the total number of plumbing fixtures in a building to estimate peak flow rates and the sizing of equipment, especially for commercial buildings.

Fixture Unit

An arbitrary unit assigned to different type of plumbing fixtures, and used to estimate flow rate and drain capacity requirements.

Flash Distillation

A distillation process in which hot water is introduced into a low pressure chamber causing some of the water to flash or quickly turn to steam.


Materials added to water which can cause gelatinous clouds of precipitate to enclose fine particles of foreign material in order to settle or filter them from the water.

Flow Controller

An in-line self pressure adjusting or orifice to regulate the flow of water or regenerant through a water conditioner.

Flow Rate

The volume of solution which passes through a given quantity of resin within a given time. Flow rate is usually expressed in terms of gallons per minute per cubic foot of resin, or as milliliters per minute per milliliter of resin. If the flow rate is greater than it should be, the water will not be completely softened or filtered.

Flush Valve (Flushometer)

A self closing valve used for flushing urinals and toilets. This type of valve allows flow rates of 15-20 gpm for up to 10 seconds.


In crossflow filtration, it is the product flow rate through a reverse osmosis, electrodialysis or ultrafiltration membrane. It is usually given in terms of volume unit per time per membrane area.


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. It may be expressed either as a linear distance or a percentage of bed depth.




A common unit of liquid volume; the US gallon has a volume of 231 cubic inches or 3.78533 liters; the British (Imperial) gallon has a volume of 277.418 cubic inches or 4.54596 liters.


Granular Activated carbon.

Galvanic Action

A form of corrosion which occurs when dissimilar metals in contact with each other and with an electrolyte causes on e of the metals to dissolve and go into solution. An example would be the result of connection copper to steel without an insulating (plastic) coupling or union. The anode metal with the higher electrode potential corrodes and the cathode is protected.

Giardia Lamblia

A common protozoan found in water and is derived from animal droppings. It can cause contagious waterborne disease characterized by acute diarrhea. It is resistant to disinfectants such as chlorine, iodine, or ultraviolet light. Giardia can be removed by filters of four micron rating.


(gr) A unit of weight equal to 1/7000th of a pound or 0.0648 gram.

Grains Per Gallon (GPG)

An expression of concentration of material in solution. One grain per gallon is equivalent to 17.1 parts per million. This is the common reference for hardness of water.

Gravel Support Bed

A layer or layers of graded gravel and course sand placed around and above the underdrain metalwork of a water treatment system. It facilitates even distribution and collection of both product water and backwash flow.


A natural mineral, primarily composed of complex silicates, which possess ion exchange properties. Greensand was the original material used in domestic and commercial water softeners and is the base product in the production of manganese greensand.


The term describing all subsurface water and the source of well water. It can be found in aquifers as deep as several miles.


A moderately insoluble calcium sulfate containing 20.9 percent water. It is often used to build soil structure and permeability.


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A geological term for rock salt, a mineral which is more than 95 percent sodium chloride. Also known as native or fossil salt.


A family of elements that includes bromine, chlorine, fluorine, astatine, and iodine. They are very active chemically. They are commonly found as the ionic component in compounds with various other elements.


A characteristic of natural water due to the presence of dissolved calcium and magnesium; water hardness is responsible for most scale formation in pipes and water heaters, and forms insoluble "curd" when it reacts with soaps. Hardness is usually expressed in grains per gallon, parts per million, or milligrams per liter, all as calcium carbonate equivalent. Temporary hardness, caused by the presence of magnesium of calcium bicarbonate, is so called because it may be removed by boiling the water to convert the bicarbonates to the insoluble carbonates. Calcium sulfate, magnesium sulfate, and the chlorides of these two metals cause permanent hardness.

Hardness Leakage

The presence in the effluent of the type of ions present in the water being treated. Leakage may be caused by incomplete regeneration, channeling, excessive service water, low temperature, high concentrations of sodium or interfering TDS in the feedwater.

Hard water

Water with a total hardness of one grain per gallon or more, as calcium carbonate equivalent.


A central piping system with two or more side outlets located at the bottom of a water conditioning system. It's purpose is to both collect product water as well as to distribute backwash water.

Head loss

The reduction on liquid pressure associated with the passage of a solution through a bed of exchange material; a measure of the resistance of a resin bed to the glow of the liquid passing through it.

Heme Iron

Organically bound iron that can give water a pinkish cast. It is found only in groundwater supplies and cannot be removed by filtration. Like soluble iron, heme iron stains fixtures with a rust or orange coloring. It may draw clear and turn yellow or pink when exposed to oxygen.


The process of purifying a kidney patients blood by means of a dialysis membrane. In this process bodily waste is transferred from the blood into a hemodialysis grade water which is beyond the membrane.


Non-disease causing bacteria


A chemical, such as sodium hexametaphosphate, added to water to increase the solubility of certain ions and to inhibit precipitation of certain chemicals. Known as a sequestering agent, it forms a thin film that protects metals from corrosion.

Hot Lime (soda softening)

Partially softens water by adding lime and soda ash at a water temperature of about 212 degrees Fahrenheit. It chemically precipitates calcium, magnesium, iron, and silica. It also drives away carbon dioxide.

Hydraulic Classification

The rearrangement of resin particles in an ion exchange unit. As the backwash water flows up through the resin bed, the particles are placed in a mobile condition wherein the larger particles settle and the smaller particles rise to the top of the bed.

Hydrogen Cycle

A complete course of cation exchange operation in which the cation medium is regenerated with acid and them all cations in the water are removed by exchange with hydrogen ions.

Hydrogen Sulfide (H2 S)

A corrosive and flammable gas produced from decaying organic matter, commonly known as "sulfur".

Hydrologic Cycle

The water cycle, including precipitation of water from the atmosphere as rain or snow, flow of water over or through the earth, and evaporation or transpiration to water vapor in the atmosphere. It is natures great water conditioner since all contaminants are left behind on the earth.

Hydro Static Pressure

A measurement of structural strength and ability to hold water pressure. Hydrostatic pressure is more challenging to a system than air pressure because air will compress and absorb impact, whereas water will not.


The term used to describe the anionic hydroxide radical (OH-) which is responsible for the alkalinity of a solution.


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The water entering a water treatment devise.

Inorganic Matter

Matter which is not derived from living organisms and contains no organically produced carbon; includes rocks, minerals and metals.

In-parallel Flow

A piping arrangement which directs separate streams through two or more water treatment units in a balanced manner, providing equal flow to each device. The inlets of two or more units are connected together and the outlets are connected together such that water will flow through the units simultaneously.

In-series Flow

A piping system in which all of the effluent flow of one unit in a water treatment system is fed to a second and succeeding unit. This arrangement achieves a greater reduction of contaminants than can be obtained by the passage through a single unit.


An atom, or group of atoms in a solution which function as a unit, and has a positive or negative electrical charge, due to the gain or loss of one or more electrons. It is smaller than a colloid.

Ion Exchange

A reversible process in which ions are released from an insoluble permanent material in exchange for other ions in a surrounding solution; the direction of the exchange depends upon the affinities of the ion exchanger for the ions present and the concentration of the ions in the solution. The ion exchanger media is an insoluble permanent solid medium. for a product offering.

Iodine Number

A measure of the ability of activated carbon to adsorb substances with low molecular weights. It is the milligrams of iodine that can be adsorbed on one gram of activated carbon.


The dissociation of molecules into simpler, electronically charged particles. It is related to the gaining or losing of electrons causing the atoms to become electronically charged.


An element often found dissolved in ground water (in the form of ferrous iron) in concentrations usually ranging from zero to 10 ppm (mg/l). It is objectionable in water supplies because of the staining caused after oxidation and precipitation (as ferric hydroxide), because of tastes, and because of unsightly colors produced when iron reacts with tannins in beverages such as coffee and tea. As little as 0.3 ppm of iron can cause staining. (See also ferrous iron, ferric iron, and heme iron).

Iron Bacteria

Organisms which are capable of utilizing ferrous iron, either from the water or from steel pipe, in their metabolism, and precipitating ferric hydroxide in their sheaths and gelatinous deposits. These organisms tend to collect in pipe lines and tanks during periods of low flow, and to break loose in slugs of turbid water to create staining, taste and odor problems.

Iron Fouling

The accumulation of iron on and within an ion exchange resin or filter bed resulting in a reduced capacity of the media.

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Jackson Turbidity Unit (JTU)

An arbitrary unit of turbidity originally based on a suspension of specific type of silica with the turbidity measured in a Jackson Candle Turbidimeter. This has been replaced by the nephelometric turbidity unit (NTU).

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A water treatment media employing copper and zinc alloy particulates which have a redox potential. KDF does not support the growth of bacteria and lasts up to twenty times longer than activated carbon. KDF 55 granules are effective in removing chlorine and other water-soluble heavy metals such as lead. KDF 85 is the choice for removing iron and hydrogen sulfide.


A unit of weight; one thousand grains, 17100 ppm, or 0.1429 pounds.


The study of the relationships between temperature, motion, and the velocity of very small particles. It is used to describe the rate of ion exchange reactions.

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Langelier Index

A calculated number that gives and indication of the tendency of water to form a protective film of calcium carbonate scale, to dissolve it or be in equilibrium with it. It does not take into account the quantities of film formed, the effect of velocities, oxygen, carbon dioxide, ammonia, silicon or natural inhibitors in the water. Therefore, it is sometimes erroneously assumed that any water that tends to dissolve calcium carbonate is automatically corrosive.

Leach Field

Area where septic tank effluent is distributed by underground piping for natural leaching and percolation through the soil.


The phenomenon in which some of the influent ions are not adsorbed and appear in the effluent. It is usually caused by an under-regenerated exchange resin bed or by excessive flow rate.


A series of bacteria, including legionella pneumophila, which can cause pneumonia-like illness called Legionnaires disease after the American Legion convention in Philadelphia where the disease first drew attention. These bacteria have been found growing in hard water scale and thrive below 140 degrees Fahrenheit in water heaters, showers, humidifiers, etc. Infection is obtained by inhalation.


The common name for calcium oxide (CaO); hydrated lime is calcium hydroxide, Ca(OH)2..

Lime Scale

Hard water scale containing a high percentage of calcium carbonate. Insoluble scale is commonly formed when water containing calcium carbonate is heated. It also forms in cold water but precipitates at a higher pH.

Lime Softening

Often used by municipalities for partial reduction of water hardness. After the addition of baked lime, soda ash is added to form an insoluble precipitate which is filtered from the water. This method leaves five or more grains of hardness.


Macroporous Resin

Ion exchange resins produced in both cation and anion versions with 12 percent or higher cross-linkage. They offer a higher resistance to oxidation and organic fouling.


One of the elements making up the earth's crust, the compounds of which when dissolved in water make the water hard. The presence of magnesium in water is a factor contributing to the formation of scale and insoluble soap curds.

Manganese (Mn)

A element sometimes found dissolved in ground water, usually with dissolved iron but in lower concentrations. It causes black stains in laundry and plumbing fixtures at concentrations higher than 0.05 mg/l. It is removed the same way as iron, by ion-exchange or oxidation and filtration.

Manganese Greensand

Greensand which has been processed to incorporate in its pores and on its surface the higher oxides of manganese. The product has a mild oxidizing power, and is often used in the oxidation and precipitation of iron, manganese and/or hydrogen sulfide, and their removal from water. It is regenerated by the use of two to four ounces of a weak solution of potassium permanganate per cubic foot of manganese greensand.


Maximum Contaminant Level. A drinking water standard. The maximum amount of a contaminant allowed in drinking water.


Maximum Contaminant Level Goal. The goal set for the maximum amount of a contaminant to be allowed in drinking water. Has not been approved to become the MCL.

Mechanical Filter

A filter primarily designed for the removal of suspended solid particles, as opposed to filters that remove contaminants by chemical means.

Microgram per Liter

Also known as parts per billion (ppb). The common symbol for microgram per liter is µg/l.


One millionth of an ohm. A unit of measurement used to test the electrical resistance of water to determine its purity. The purer the water, the greater its resistance to conducting an electrical current. Water of absolute purity has a resistance of eighteen million ohms across one centimeter at a temperature of twenty-five degrees Celsius.


One millionth of a mho. Used to measure the conductivity and the approximate TDS content of water. Absolute pure water has a conductivity of 0.055 micromhos per centimeter at 25 degrees Celsius. Also known as micro Siemens. The specific conductance is the reciprocal of resistance, therefore MHO is OHM spelled backwards.


A linear measure equal to one millionth of a meter, or .00003937 inch. The symbol for the micron is the Greek letter "µ". The smallest particle visible to the human eye is 40 microns. Most types of bacteria range from 0.05 to 10.0 microns in size.

Micron Rating

The term applied to a filter or filter medium to indicate the particle size above which all suspended solids will be removed, throughout the rated capacity. As used in industry standards, this is an "absolute", not "nominal" rating..

Milligram per Liter

(mg/l) A unit concentration of matter used in reporting the results of water and wastewater analyses. In dilute water solutions, it is practically equal to the part per million, but varies from the ppm in concentrated solutions such as brine. As most analyses are performed on measured volumes of water, the mg/l is a more accurate expression of the concentration, and is the preferred unit of measure.


A term applied to inorganic substances, such as rocks and similar matter found in the earth's strata, as opposed to organic substances such as plant and animal matter. Minerals normally have definite chemical composition and crystal structure. The term is also applied to matter derived from minerals, such as the inorganic ions found in water. The term has been incorrectly applied to ion exchangers, even though most of the modern materials are organic ion exchange resins.


The simplest combination of atoms that will form a specific chemical compound; the smallest particle of a substance which will still retain the essential composition and properties of that substance, and which can be broken down only into atoms and simpler substances.

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A membrane process that treats water between reverse osmosis and ultrafiltration the filtration/separation spectrum. It can remove particles in the 300 to 1,000 molecular weight range such as humic acid and organic color found in water. Nanofiltration may be used for selective removal of hardness ions.

Nephelometric Turbidity Unit (NTU)

The standard unit of measurement used to measure turbidity in water. It makes use of a light scattering effect of fine suspended particles in a light beam. The NTU has replaced the Jackson Turbidity Unit (JTU) as the standard of measurement.


A common designation for alkaline materials such as calcite (calcium carbonate) or magnesia (magnesium oxide) used in the neutralization of acid waters. Alkaline water can also be neutralized by the addition of an acid. The neutral point of the pH scale is 7.0, indicating the presence of equal numbers of free hydrogen and hydroxide ions.


Abbreviation for National Sanitation Foundation Testing Laboratory

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A unit of measure determining the resistance to passage of an electrical current. In a solution, it is related to the electrolyte concentration in the solution.

Operating Pressure

The range of pressure, usually expressed in pounds per square inch, over which a water conditioning device or water system is designed to function. Usually 30-100 psi.


Having the characteristics of or being derived from plant or animal matter, as opposed to inorganic matter derived from rocks and minerals. Organic matter is characterized by its carbon-hydrogen structure.

Organics ( i.e., Organic Chemicals)

Term used to describe any or all of the compounds with chemical structures based on carbon. Examples are hydrocarbons, wood, sugars, proteins, methane, petroleum-based compounds, solvents, pesticides, herbicides, trihalomethane (THM) and trichloroethylene (TCE).


A process of diffusion of a solvent such as water through a semi-permeable membrane which will transmit the solvent but impede most dissolved substances. The normal flow of solvent is from the dilute solution to the concentrated solution. Osmosis causes the stronger solution to become more diluted and tends to equalize the opposing solutions.

Osmotic Pressure

The pressure and potential energy difference that exists between solutions on either side of a semi-permeable membrane. This pressure is caused by the tendency of water to flow in osmosis. Every 100 ppm (mg/L) of TDS produces about one pound per square inch of osmotic pressure. Osmotic pressure must first be overcome by water pressure in the reverse osmosis process.

Oxalic Acid

Can be used for the removal of iron stains from most washable fabrics. Oxalic acid crystals can be obtained at most drug stores. It is poisonous and a skin irritant, therefore precautions must be used.


A chemical process in which electrons are removed from an atom, ion or compound. The addition of oxygen is a speciform of oxidation. Combustion is an extremely rapid form of oxidation, while the rusting of iron is a slow form. Oxidation never occurs alone but always as a part of the oxidation-reduction (redox) reaction.

Oxidizing Agent

A chemical substance that brings about the oxidation of other substances in chemical oxidation and reduction reactions. Examples of oxidizing agents include oxygen, ozone, chlorine and peroxide.

Oxidizing Filter

A type of filter used to change the valence state of dissolved molecules, making them insoluble and therefore filterable. For example, a filter that oxidizes ferrous iron, manganous manganese, and/or anionic sulfur by use of a catalytic media such as manganese oxide and then filters the oxidized precipitant out of the water.


An unstable form of oxygen (03), which can be generated by sending a high voltage electrical discharge through air or regular oxygen. It is a strong oxidizing agent and has been used in water conditioning as a disinfectant. It can be also produced by some types of ultraviolet lamps and during lightning storms.

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A term used to describe visible sediment particles, used as both singular and plural.

Parts Per Billion (ppb)

A basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of a dissolved or suspended constituent, per billion parts by weight of water or other solvent. One part per billion is equal to one microgram per liter, the preferred unit.

Parts Per Million (ppm)

A common basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of water or other solvent. In dilute water solutions, one part per million is practically equal to one milligram per liter, which is the preferred unit. 17.l ppm equals one grain per US gallon. One ppm equals one pound per million pounds of water.

pH (potential of Hydrogen)

An expression of the acidity of a solution; the negative logarithm of the hydrogen ion concentration (pH 1 very acidic; pH 14, very basic; pH 7, neutral). e.g., pH 5 is 10 times the acidity of 6 and 100 times the acidity of 7. pH is a measure of intensity and not capacity. It is the logarithm of the reciprocal of the hydrogen ion concentration of a solution. The neutral point of 7 indicates the presence of equal concentrations of free hydrogen and free hydroxide ions.

Pharmaceutical Grade Water

The definition of six grades of water by the U.S. Pharmacopoeia is as follows: 1.) Purified water 2.) Water for injection 3.) Bacteriostatic water for injection 4.) Sterile water for inhalation 5.) Sterile water for injection 6.) Sterile water for irrigation.


An acid-base indicator which produces no color in an acid solution but turns pink or red in an alkaline solution.

Physical Adsorption (Van der Waals Adsorption)

Binding of adsorbate to the surface of a solid by forces whose energy levels approximate those of condensation.

Physical Stability

The quality which an ion exchange resin must possess to resist changes that might be caused by attrition, high temperatures, and other physical conditions.

Point of Entry (POE)

A water treatment device which installs at the main inlet to a building and acts as centralized treatment.

Point-of-Use (POU)

A water treatment system designed to connect at the actual point-of-use for water; countertop or undersink treatment systems.


A sequestering agent used to tie up hardness and iron in solution. As a coating agent, it forms a thin passivating film on metal surfaces to control corrosion.


The complex network of channels in the interior of a particle of a sorbent.

Portable Exchange

Water softeners, deionizers, and filters which are designed for removal from its point of application for transport to a central station or plant for regeneration or servicing.

Positive Charge

The electrical potential acquired by an atom which has lost one or more electrons; a characteristic of a cation.

Potable Water

Water which is considered safe and fit for human consumption, culinary and domestic purposes and meets the requirements of the health authority having jurisdiction.

Powdered Activated Carbon

Activated carbon in particle sizes predominantly smaller than 80 mesh.


The abbreviation for "parts per billion".


The abbreviation for "parts per million".


The application of chlorine to a water prior to other water treatment processes.


To cause a dissolved substance to form a solid particle that can be removed by settling or filtering. The term also refers to the solid thus formed.

Preferential Adsorption

Adsorption in which a certain component or certain components are adsorbed to a much greater extent than others.

Pressure Drop

A decrease in water pressure during its flow due to internal friction between molecules of water, and external friction due to irregularities or roughness in surfaces past which the water flows.


Any of a large group of mostly microscopic, one celled animals living chiefly in water. Many protozoa's are parasitic and are higher on the food chain than the bacteria they eat.


A natural, glassy aluminum silicate mineral from volcanic ash which is used as a water treatment filtration media.


The removal of undesirable matter from water or wastewater. It is the disinfection of water by the killing of microbial contaminants, such as coliform bacteria. A strict definition means the removal from water of all contaminants.


Biological decomposition of organic matter by microbes with the production of ill smelling products. Usually takes place when there is a deficiency of oxygen.


Substances which produce fever when introduced into humans. Being chemically stable, pyrogens are not necessarily destroyed by conditions that kill bacteria. Pyrogenic means to cause heat.


A super oxidation media serving as a catalyst in the removal of iron, hydrogen sulfide and manganese. It works best at or above a pH of 6.5 and requires no regeneration. Adequate backwashing is necessary to provide at least 20 per cent bed expansion of this 120 lb. per cubic foot media.

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Quartz Sleeve

Also called a quartz jacket, it is a clear, pure quartz sleeve that is installed around the high intensity ultraviolet lamp in an ultraviolet system. It retards less than 10 percent of the radiation dosage in contrast to the poorer results offered by glass.



Naturally occurring radioactive elements such as radium 226 and radium 228 created in the decay of the uranium and thorium series. It can be removed from water by cation exchange softening.


A short lived radioactive gas produced from decaying uranium that is soluble in water. Can be effectively removed by activated carbon filtration or serration. Radon is considered carcinogenic when inhaled by humans.

Raw Water

Untreated water from wells or from surface sources or any water before it reaches a water treatment device or process.

Reactivation (Revivification)

Oxidation processes for restoring the adsorptive properties of a spent sorbent such as activated carbon.


A shortened term for oxidation-reduction. A reaction where electrons are gained or lost and new elements are formed.


The solution used to restore the activity of an ion exchanger. Acids are employed to restore a cation exchanger to its sodium form. The anion exchanger may be rejuvenated by treatment with an alkaline solution. Potassium permanganate is used to regenerate a manganese greensand iron and manganese iron and manganese removal filter.


The process of returning the sodium ions to the mineral after it has exchanged all its sodium ions for calcium and magnesium from hard water. This is accomplished by first back-washing the mineral bed to free it of all foreign matter, them passing salt brine through the mineral. The sodium ions attach themselves to the mineral, and the calcium and magnesium combine with the chloride from the brine to form calcium and magnesium chlorides, which are rinsed down the drain. All water softeners using the ion-exchange process are regenerated with these basic steps. In similar fashion cation and anion components of a demineralizer as well as manganese greensand are recharged with comparable sequences.


In crossflow membrane filtration and deionization, it is the ability of the membrane to reject the passage of dissolved solids and other contaminants into the product water.


The amount of a specific material remaining in the water following a water treatment process. It may refer to material remaining as the result of incomplete removal such as hardness leakage, or to a substance meant to remain in the treated water such as residual chlorine.


Synthetic organic ion exchange material, such as the high capacity cation exchange resin widely used in water softeners. Technical name- sulfonated co-polymer of styrene and divinyl benzene.


The ability of an adsorbent to resist desorption of an adsorbate.

Reverse Deionization

The use of an anion exchange unit ahead of a cation exchange unit- in that order- in a deionization system.

Reverse Osmosis

A process for the removal of dissolved ions from water, in which pressure is used to force the water through a semi-permeable membrane, which will transmit the water but reject most other suspended and dissolved materials. It is called reverse osmosis because mechanical pressure is used to force the water to flow in the direction that is the reverse of natural osmosis, namely from the dilute to the concentrated solution.


The abbreviation for "reverse osmosis".

Rust (ferric oxide)

A reddish product of corrosion sometimes found in water. Rust is formed as a result of electrochemical interaction between iron and oxygen in the presence of moisture.

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Sacrificial Anode

An anode constructed of magnesium or other suitable material and placed in a water heater tank to accept the electrolytic activity and to protect the tank from corrosion.

Sand Filter

A treatment device or structure for removing solid or colloidal material of a type that cannot be removed by sedimentation. Such filters can be gravity rapid-rate or enclosed pressure type.


The common name for the specific chemical compound sodium chloride (NaCl), used in the regeneration of ion exchange water softeners. In chemistry, the term is applied to a class of chemical compounds which can be formed by the neutralization of an acid with a base.

Saturated Solution

A solution containing the maximum amount of the dissolved substance that such a solution can hold at this temperature.


A polymer matrix or ion exchanger used to remove organics from feedwater prior to a deionization process.

Secondary treatment

The second step in treating wastewater to remove suspended and dissolved solids and biochemical oxygen (BOD) after the initial primary treatment.

Selective Ion Exchange

The use of a selective ion exchange medium with the property of removing specific ions from a solution.


A chemical reaction in which certain ions are bound into a stable, water soluble compound, thus preventing undesirable action by the ions. For example, polyphosphates can sequester hardness and prevent reactions with soap.

Service Run

That portion of the operating cycle of a water conditioning unit during which treated water is being delivered, as opposed to the period when the unit is being backwashed, recharged or regenerated.

Siliceous Gel Zeolite

A synthetic, inorganic exchanger produced by the aqueous reaction of alkali with aluminum salts.

Soda Ash

The common name for sodium carbonate, a chemical compound used as an alkaline builder in some soap and detergent formulations, to neutralize acid water, and in the lime- soda ash water treatment process.

Sodium Hydrosulfite

A strong reducing agent used as the main ingredient of several resin cleaners used to clean iron fouled in ion exchange resin beds.

Softened Water

Any water that is treated to reduce hardness minerals to 1.0 GPG (17.1 mg/L) or less, expressed as calcium carbonate.


The liquid, such as water, in which other materials (solutes) are dissolved.


A yellowish solid chemical element. The term is also used as a slang expression to refer to water containing hydrogen sulfide gas (H2 S).


The expansion of an ion exchange bed which occurs when the reactive groups on the resin are converted from one form to another. This property is reversible and indeed, some resins shrink in the exhausted state.

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TCE (Trichloroethylene)

A toxic volatile organic chemical typically used as an industrial solvent.


The abbreviation for "total dissolved solids".


A naturally occurring substance in wood, grapeskins, seeds and stems. Is primarily responsible for the basic "bitter" component in wines. Acts as a natural preservative, helping the development and, in the right proportion, balance of the wine. Considered a pollutant when present in excess.

Tertiary Treatment

The third stage in the treatment of sewage that in a high degree of conditioning following the reduction of pollutants accomplished by the primary and secondary stages of treatment.

Thin-film Composite Membrane (TFC)

Reverse osmosis membrane produced with polyamide-based polymer. It is resistant to bacteria and can withstand a wide pH range. However, it cannot tolerate chlorine.

Throughput Volume

The amount of solution passed through an exchange bed before exhaustion of the resin is reached.

Total Acidity

The total of all forms of acidity, including mineral acidity, carbon dioxide, and acid salts. Total acidity is usually determined by titration with a standard base solution to the phenolphthalein endpoint (pH 8.3).

Total Alkalinity

The alkalinity of a water as determined by titration with standard acid solution to the methyl orange endpoint (pH approximately 4.5); sometimes abbreviated as "M alkalinity". Total alkalinity includes many alkalinity components, such as hydroxides, carbonates, and bicarbonates.

Total Chlorine

The total amount of chlorine is a solution, which includes the combined chlorine as well as the free available chlorine.

Total Dissolved Solids

The weight of solids per unit volume of water which are in true solution, usually determined by the evaporation of a measured volume of filtered water, and determination of the residue weight. TDS is expressed as ppm per unit volume of water. An electrical conductivity test provides only an estimate of the TDS since non-conductive substances cannot be measured by electrical means.

Total Hardness

The sum of all hardness components in a water, expressed as their equivalent concentration of calcium carbonate. Primarily due to calcium and magnesium in solution, but may include small amounts of metals such as iron which can act like calcium and magnesium in certain reactions. These minerals are scale forming, affect taste and color of certain foods and react with soap to form insoluble soap curds.

Total Organic Carbon

The measurement of carbon dioxide produced from organics when a water sample is atomized into a combustion chamber. The amount of carbon covalently bound in organic compounds in a water sample.

Total Solids

The weight of all solids, dissolved and suspended, organic and inorganic, per unit volume of water; usually determined by the evaporation of a measured volume of water at 105 degrees Celsius in a pre-weighed dish.

Trihalomethanes (THM's)

A group of organic chemicals to known to be carcinogenic in more than trace amounts which are produced from chlorination. They reduce the germicidal activity of chlorine in alkaline water.


A measure of the amount of finely divided suspended matter in water, which causes the scattering and adsorption of light rays. Turbidity is usually reported in arbitrary nephalometric turbidity units (NTU) determined by measurements of light scattering. NTU should not exceed 0.5 in potable water. Turbidity can protect bacteria from sterilization.

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A membrane type system that removes small colloids and large molecules from solutions. Ultrafiltration removes particles in size range between 0.002 to 0.1 micron range. The process falls between reverse osmosis and microfiltration as far as the size of particles removed is concerned.

Ultrapure Water

No standards exist describing ultrapure water though it is not considered to be sterile. It is water that has been deionized and provides high resistivity and contains no organics.

Ultraviolet Light

Radiation having a wave length shorter than 4000 angstroms (visible light) down to 100 angstroms on the border of the x-ray region. Ultraviolet light is used as a disinfectant.


The operation of an ion exchange unit in which solutions are passed in at the bottom and out at the top of the container.


A radioactive metallic element found naturally in combination with other materials. Uranium 238 is the most common form.

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A tube with a tapered throat which causes an increase in velocity thus a decrease in pressure of the fluid passing through it. It is the common item used to educt or suck a regenerant into a water conditioning system.


The smallest form of life known to be capable of producing disease or infection, usually considered to be of large molecular size. They multiply by assembly of component fragments in living cells, rather than be cell division, as do most bacteria. Being parasitic infectious microbes, they are much smaller than bacteria.

Volatile Organic Compounds (VOC's)

Synthetic organic chemicals that vaporize at relatively low temperatures.

Void area

The space between the resin beads in an ion exchange bed or the space between the particles of filter media bed. Also can be defined as the space between the chunks of salt in a brine tank.

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Water Conditioning

Virtually any form of water treatment designed to improve the quality of water, by neutralization, inhibition or removal of undesirable substances.

Water Hammer

The shock wave produced by the abrupt change of water flow through a piping system. Water hammer produces an instantaneous multiple increase in the pressure normal to the system. The installation of a water hammer arrestor will absorb these shock waves.

Water Softening

The reduction or removal of calcium and magnesium ions which are the principle cause of hardness in water.


Water Quality Association. Many participants in the POU and POE water conditioning industry are members of this association.

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A volatile organic chemical (VOC) commonly used in industry as a solvent.

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Naturally occurring or synthetic hydrated sodium alumina silicate with ion exchange properties. Zeolites have been largely replaced with synthetic organic cation ion exchange resins.

Modified Zeolites can be selectively charged with exchange minerals such as potassium and used to remove undesirable elements such as iron, hydrogen, sulfide, and manganese.

Zero Soft

Water with a total hardness less than 1.0 grain per US Gallon (17.1 ppm), as calcium carbonate.