Water Treatment Glossary


Used in reference to micron rating of cartridge filters. Refers to an exact size of particlesthat will not pass through, and all particles larger than that size are trapped within the filter. Hence, a one micronabsolute filter is one that will trap all particles larger than one micron.
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.
Acid Demand
A measure of the amount of acid required to reduce pH to a predetermined level. This canbe accomplished by use of an acid filtration procedure (Acid Demand Test).
Ability to neutralize alkaline (hi pH) substances.
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 form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions.
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.
The process by which molecules or colloids physically adhere to the surfaces of solids. Filtercarbon adsorbs organic chemicals.
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 or method of bringing about intimate contact between air and a liquid.
Aeration Tank
A chamber for injecting air into water.
Requiring free oxygen for respiration. Refers to types of bacteria commonly found in water and wastewater treatment systems.
Aerobic Bacteria
Bacteria that requires free (elementary) oxygen for growth.
Aggressive Water
A term usually applied to waters containing acid or oxygen which hasten corrosion (rusting).
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.
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.
Ability of substance to neutralize acids. Typically measured as ppm (mg/l) of CaCO3.
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.
A biological environment that is deficient in all forms of oxygen, especially molecular oxygen, nitrates and nitrites. The decomposition by microorganisms of waste organic matter in wastewater in the absence of dissolved oxygen is classed as anaerobic.
Anaerobic Bacteria
Bacteria that grows in the absence of free oxygen and derive oxygen from breaking down complex substances.
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.
Negatively charged ion.
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.
Anionic Flocculant
Negatively charged flocculant. Used in water treatment to aid solid / liquid separation
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.
A biological environment that is deficient in molecular oxygen, but may contain chemically bound oxygen, such as nitrates and nitrites.
Abbreviation for American National Standards Institute.
A material used to control scale formation in water systems such as boiler or cooling water systems.
Containing water; watery.
Any geological formation containing water; one that supplies water for wells, springs, etc.
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
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.


Back Pressure
Pressure which creates resistance against the flow of water.
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.
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.
Balanced Water
Water that is neither corrosive nor scaling (in relation to pH, total alkalinity, calciumhardness, and temperature factors). The Langelier Index for perfectly balanced water equals zero.
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.
Base Demand
A measure of the amount of alkali material required to raise pH to a predetermined level.This can be accomplished by use of a base titration procedure (Base Demand Test).
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.
When used in reference to cartridge filters, refer to chemicals used to hold, or bind, shortfibers together in a filter.
Biochemical Oxygen Demand
Common analytical test to determine organic (food) content of water. It measures oxygen consumption by microorganisms as they degrade the organic content in water. Most frequently used test method is a 5 day BOD: BOD5
Chemical substance designed for killing living organisms in water. Often characterized by type of organism killed: bactericide, fungicide or algaecide.
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.
Biological Oxidaiton
The process by which bacteria and other types of micro-organisms consume dissolved oxygen and organic substances in waster water, using the energy released to convert organic carbon into carbon dioxide and cellular material.
The trade name for a manganese dioxide coated aluminum silicate used as an oxidizing catalyst filter medium for iron and manganese reduction.
The fouling or plugging of pores in a membrane, usually a gel-like substance.
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
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.
Chemical sanitizer that kills bacteria and algae.
A chemical which causes a solution to resist changes in pH, or to shift the pH to a specific value.
Bulking Sludge
A phenomenon that occurs in activated sludge plants whereby the sludge occupies excessive volumes and will not concentrate readily. This condition refers to a decrease in the ability of the sludge to settle and consequent loss over the settling tank weir. Bulking in activated sludge aeration tanks is caused mainly by excess suspended solids (SS) content. Sludge bulking in the final settling tank of an activated sludge plant may be caused by improper balance of the BOD load, SS concentration in the mixed liquor, or the amount of air used in aeration.
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.


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.
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.
Calcium Hardness
A measure of the calcium salts dissolved in water.
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.
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.
Cationic Flocculant
A positively charged high molecular weight polyelectrolyte water soluble organic polymer designed to agglomerate solids in water substrates.
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
Common analytical test to determine the theoretical oxygen consumed in oxidizing all of the organic and any oxidizable inorganic content of water. It is used to measure the pollution strength of water.
Chemical Solution Feeder
A pump used to meter chemicals such as chlorine or polyphosphate into a watersupply.
Chemical Stability
Resistance to chemical change which ion exchange resins must posses despite contact with aggressive solutions.
A combination of free chlorine and ammonia gas that retains its bactericidal qualities fora longer time than does free chlorine. It is less effective than chlorine as a disinfectant, but is often used becauseit reduces the harmful by-product chemicals produced by free chlorine. It is becoming more common as the standard disinfectantused by municipal water supplies. In general, it is more difficult to remove from water than free chlorine.
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.
The application of chlorine to water, sewage, or industrial wastes, generally for the purpose of disinfection, but frequently for accomplishing other biological or chemical results.
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.
Chemical sanitizer that kills bacteria and algae. A very toxic biocide. A halogen element isolatedas a heavy irritating greenish-yellow gas of pungent odor used especially as a bleach, oxidizing agent and a disinfectantin water purification.
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.
Chlorine, Combined
The reaction product of chlorine with ammonia or other pollutants; also known as chloramines.
Chlorine, Free
Chlorine available to kill bacteria or algae. Chlorine that has not combined with othersubstances in water.
Clean In Place
Is a method of cleaning the interior surfaces of pipes, vessels, process equipment, filters and associated fittings, without disassembly.
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.
The destabilization for repulsive electrical charges to permit agglomeration of colloid particles in water. This process aids the clarification of water.
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.
Coliform Organisms
A group of bacteria recognized as indicators of fecal pollution (see also escherichia coliform).
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.
A gelatinous or mucinous substance suspended in water that can pass through even thefinest sediment filter.
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.
Combined Sewer
Carries both sanitary sewage and storm water run-off.
Decline in flux as a result of applied pressure compressing a reverse osmosis or ultrafiltrationmembrane.
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.
Composite Sample
To have significant meaning, samples for laboratory tests on wastewater should be representative of the wastewater. The best method of sampling is proportional composite sampling over several hours during the day. Composite samples are collected because the flow and characteristics of the wastewater are continually changing. A composite sample will give a representative analysis of the wastewater conditions.
The portion of a feed stream that retains the ions, organics and suspended particles thatwere rejected during the crossflow filtration process. (In other words, the rinse water from a reverse osmosis unit.)
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.
Object that is a source of contamination.
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.
Term to describe compound used in water treatment to aid precipitation of substances normally soluble under the conditions employed. Common co-precipitants used in water are iron, aluminum, calcium and magnesium.
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.
Corrosion Inhibitor
Chemical additive designed to control / minimize metal corrosion in water system.
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 precise separation of the components of a fluid by semi-permeable membrane through the applicationof pressure and flow.
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.
Cyanuric Acid
Chemical used to prevent the decomposition of chlorine by ultra-violet (UV) light.
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.
Cycles of Concentration
The ratio of boiler or cooling water to make up (feed water). Typically measured by monitoring total dissolved solids, conductivity, silica or chlorides.


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.
The process of removing minerals from water, e.g. deionization, reverse osmosis anddistillation.
Chemical additive that destroys the emulsifying characteristics water. Typically used separate stabilized (emulsified) oil in water.
Wastewater treatment process involved in the biological removal of nitrogen in which the nitrite (NO2) is converted to nitrogen gas (N2)
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.
Removing free water from a sludge or slurry to form a high solids cake. Recessed Chamber Filter presses, Belt Presses, centrifuges, rotary fan presses and vacuum presses are dewatering devices.
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.
Diffused Air
Method of aeration.
The biochemical decomposition of organic matter that results in the formation of mineral and simpler organic compounds.
Destruction of bacteria in a water supply or distribution system.
A non-surface active compound or an active substance added to a suspension, usually a mix, to increase the separation of particles and to prevent subsiding or clumping.
Dissolved Air Flotation
Method of removing oil and suspended solids.
Dissolved Air Flotation Clarifier
A piece of equipment that used dissolved air to float suspended solids from water. Typically used when the suspended solids have a lower density than water.
Dissolved Oxygen
The measurement of the gaseous oxygen (O2) concentration in water.
Dissolved Solids
Solids physically suspended in sewage that cannot be removed by proper laboratory filtering.
Steam from boiling water is condensed on a cool surface, collected and stored. Most contaminantsdo not vaporize and therefore do not pass to the condensate. Removes nearly 100 percent of salts and those organics thatdo not have a vaporizing temperature near or below that of water.
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.


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.
Electro Deionization
A water treatment technology that utilizes an electricity, ion exchange membranes and resin to deionize water and separate dissolved ions (impurities) from water.
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.
A basic building block of the system. Often used in reference to membrane element; part of systemcontaining the membrane for use in separations.
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.
Emulsion Breaker
Chemical additive that destroys the emulsifying characteristics water. Typically used separate stabilized (emulsified) oil in water.
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
Escherichia Coliform
A species of bacteria found in large numbers in the intestinal tract of warm-blooded animals.
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.
Extended Aeration
A modification of the activated sludge process which provides for aerobic sludge digestion within the aeration system.


The input solution to a system.
Ferric Chloride
A metal salt (FeCl3) commonly used as an coagulant in water clarification and as etching agent in chemical-etching.
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
Filter Cube
The accumulate particles on a filter surface.
Filter Press
A solids dewatering device that uses pressure differential applied to sludge within a series of plates with filter clothes. The plates (with clothes in them) are arranged in a plate pack with the sludge filling chambers created by recesses within each plate. Filter presses are often called Recessed Chamber or Plate and Frame Filter Presses.
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 portion of the feed stream that has passed through the membrane.
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.
The agglomeration of smaller particles in gelatinous mass that can be more easily removed from the liquid than the individual small particles.
High molecular weight polyelectrolyte water soluble organic polymer designed to agglomerate solids in water substrates. Characteristics of flocculants in water treatment are determined by their molecular weight, charge type (anionic, nonionic or cationic) and charge density.
The coming together of coalescing and minute particles in a liquid.
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
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.


Granular Activated carbon.
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.
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.
Gallons per day.
Grains per gallon. Equal to 17.1 mg/l. This is the most common measurement for hardness.
(gr) A unit of weight equal to 1/7000th of a pound or 0.0648 gram.
Grains Per Gallon
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.
Gray Water
Reusable wastewater from residential, commercial and industrial bathroom sinks, bath tub shower drains, and clothes washing equipment drains.
In wastewater, a group of substances, including fats, waxes, free fatty acids, calcium and magnesium soaps, mineral oils, and certain other non-fatty materials.
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.
Heavy, inorganic matter, such as sand or pebbles.
Ground Water
Water confined in semipermeable rock layers. Well water, in other words.
A moderately insoluble calcium sulfate containing 20.9 percent water. It is often used to build soil structure and permeability.


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.
Hard water
Water with a total hardness of one grain per gallon or more, as calcium carbonate equivalent.
The typically the concentration of calcium and magnesium salts in water. However, it may include other metal salts such as Al, Mn, Sr and Zn. Normally measured as CaCO3 equivalents.
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.
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.
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.
Heavy Metals
Metals having a high density or specific gravity. A generic term used to classify contaminantssuch as cadmium, lead and mercury.
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.
A type of bacteria that uses organic matter for energy and can use free oxygen, nitrates or sulfates as and oxygen source for respiration.
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
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.
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.
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
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.
The term used to describe the anionic hydroxide radical (OH-) which is responsible for the alkalinity of a solution.


Inclined Plate Clarifier
A solids / liquid separation device (clarifier) that is filled with parallel (sometimes called Lamella) plates that are inclined at an angle between 45 and 55 degrees. The plates reduce (compared to a gravity clarifier) the foot print required to properly settle solids.
Introduction of presence of pathogenic organisms in potable water supply.
The water entering a water treatment devise.
Inorganic Material
Material that will not respond to biological action (sand, cinders, stone). Non-volatile fraction of solids.
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.
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.
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.
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.


Jackson Turbidity Unit
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).


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.


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.
Magnesium Hardness
A measure of the magnesium salts dissolved in water. It is not a factor in water balance.
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.
A material layer that is a selective barrier between two phases and remains impermeable to specific particles, molecules or substances.
Membrane Bio Reactor
Aerobic biological waste water treatment process that utilizes membrane filtration (rather than clarification) for solids / liquid separation. The membrane filters (ultra filters) can be either submerged or external to the biological mixed liquor tanks.
Micro Filtration
A type of membrane filtration that separates suspended solids and solutes of high molecular from a liquid and low molecular weight solutes. This separation process is used in industry processes, water treatment and research for purifying and concentrating macromolecular solutions.
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.
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..
Microscopic plants and animals such as bacteria, molds, protozoa, algae, and small metazoa.
Basically, a measurement of water conductivity and therefore a way to state “parts per million”of total dissolved solids. In general terms, 1.4 microsiemens = 1ppm (parts per million) of dissolved solids. However,for calcium carbonate the relationship is 2.0 microsiemens = 1 ppm of calcium carbonate.
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.
Mixed Bed Ion Exchange
Is anion exchange process that uses a mixture of cation and anion resin combined in a single ion exchange column. With proper pretreatment, product water purified from a single pass through a mixed bed ion exchange column is the purest that can be made.
Mixed Liquor
The combination of primary effluent and active biological solids (return sludge) in the activated sludge process that is fed into the aeration tank.
Mixed Liquor Suspended Solids
The milligrams of suspended solids per liter of mixed liquor that are combustible at 550 degrees Centigrade. An estimate of the quantity of MLSS to be wasted from the aeration tank of an extended aeration plant may be determined by the rate of settling and centrifuge tests on the sludge solids.
Mixed Media Gravity Filter
A filter using more than one filtering media (such as coal and sand.)
The membrane element combined with membrane element housing.
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.
Moving Bed Bio Reactor
Aerobic biological waste water treatment process that utilizes the fixed film (media) process. High surface area media is suspended in biological mixed liquor and bacteria grow on the media (attached growth) surface. A clarifier is typically used downstream of the MBBR for solid / liquid separation.
Muriatic Acid
An acid used to reduce pH and alkalinity. Also used to remove stain and scale.


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.
Nephelometer Turbidity Units
A measurement of the clarity (turbidity) of a liquid.
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.
The conversion of nitrogen matter into nitrates by bacteria.
Nitrogen is present in wastewater in many forms total Kjeldahl nitrogen, ammonia nitrogen, organic nitrogen.
Nitrogen Cycle
The cycle of life, death, and decay involving organic nitrogenous matter is known as the nitrogen cycle. In the nitrogen cycle ammonia is produced from proteins.
When used in reference to micron rating of cartridge filters, refers to an approximate size particlethat will not pass through a filter. Thus, a nominal one-micron filter is one that gets most of the particles larger thanone micron. See also Absolute.
A neutral charged high molecular weight polyelectrolyte water soluble organic polymer designed to agglomerate solids in water substrates.
Abbreviation for National Sanitation Foundation Testing Laboratory
Any substance assimilated by organisms that promotes growth and replacement of cellular constituents.


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.
Organic Material
Material that can be broken down by bacteria (fats, meats, plant life).
Organic Matter
The waste from homes or industry of plant or animal origin. Volatile fraction of solids.
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 simple compound of phosphorous and oxygen that is soluble in water.
The spontaneous flow of water from a less concentrated solution to a more concentrated solutionthrough a semipermeable membrane occurring until energy equilibrium is achieved.
Osmotic Pressure
Measurement of the potential energy difference between the solutions on either sideof a semipermeable membrane.
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 biological environment which is aerobic.
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.
Oxidation Ponds or Lagoons
Holding ponds designed to allow the decomposition of organic wastes by aerobic or anaerobic means.
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.


A term used to describe visible sediment particles, used as both singular and plural.
Parts Per Billion
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
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.
Allowing some material to pass through.
The portion of the feed stream that passes through the membrane. This term is applied to the”product water” of a reverse osmosis unit–the finished water that you drink.
A measure of the acidity of water. The pH scale runs from 0 to 14 with 7 being the mid-point or neutral.A pH of less than 7 is on the acid side of the scale with 0 as the point of greatest acid activity. A pH of more than 7is on the basic (alkaline) side of the scale with 14 as the point of greatest basic activity.
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.
Phenol Red
Chemical reagent used for testing pH in the range of 6.8 – 8.4.
An acid-base indicator which produces no color in an acid solution but turns pink or red in an alkaline solution.
Physical 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
A water treatment device which installs at the main inlet to a building and acts as centralized treatment.
A water treatment system designed to connect at the actual point-of-use for water; countertop or undersink treatment systems.
Synthetic chemicals used as a coagulant aid.
A chemical compound with many repeating structural units.
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.
An opening in a membrane which allows certain components to pass through, but not others.
A material which allows certain substances to pass through its pores.
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 fit for human consumption.
Powdered Activated Carbon
Activated carbon in particle sizes predominantly smaller than 80 mesh.
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.
Primary Waste Treatment
Mechanical separation of solids, grease, and scum from waste-water. With the aid of flocculating agents, primary treatment can eliminate 50% t 65% othe suspended solids. Solids removed by the primary treatment may comprise as much as 30% t40% othe original BOD of the water.
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.
Pounds per square inch (pressure).
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.


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.


The abbreviation for “reverse osmosis”.
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 Wastewater
Wastewater before it receives any treatment.
Raw Water
Untreated water from wells or from surface sources or any water before it reaches a water treatment device or process.
Oxidation processes for restoring the adsorptive properties of a spent sorbent such as activated carbon.
A tank where a wastewater stream is mixed with bacterial sludge and biochemical reactions occur.
Receiving Waters
Rivers, lakes, or other water sources that recieve treated or untreated waters.
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.
Specially manufactured polymer beads used in the ion exchange process to remove dissolved saltsfrom water.
The ability of an adsorbent to resist desorption of an adsorbate.
Return Activated Sludge
Activated return sludge is normally returned continuously to the aeration tank. Recycling of activated sludge back to the aeration tank provides bacteria for incoming wastewater. Its should be brown in color with no obnoxious odor and is often also returned in small portions to the primary settling tanks to aid sedimentation. Settled activated sludge is generally thinner than raw sludge. Some activated sludge will be wasted to prevent excessive solids build up.
Return Sludge
Settled activated sludge returned to mix with incoming raw or primary settled wastewater. When the return sludge rate in the activated sludge process is too low, there will be insufficient organisms to meet the waste load entering the aerator.
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.
Reverse Osmosis
Water purification technology that uses a semipermeable membrane to remove dissolved solids, molecules and larger particles from water. Applied pressure is used to overcome osmotic pressure and produce high purity water. Reverse osmosis is used to produce ultra pure water for a variety of applications.
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.


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.
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.
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.
Saturated Solution
A solution containing the maximum amount of the dissolved substance that such a solution can hold at this temperature.
Crust of calcium carbonate, the result of unbalanced pool water. In general, it refers to calciumbuildup in pipes or the interior of appliances like hot water heaters.
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.
Secondary Waste Treatment
Secondary treatment is part of the primary treatment in that the wastewater continues from the equalization tank and sludge holding zone where it loses the most solids. From the primary stages it passes to the aeration zone where it continues to be broken down and separated from any solids. After aeration the wastewater will pass to the clarifier and disinfection zones. Some plants will include a tertiary treatment that typically involves clorination or UV treatment.
Sedimentation Tanks
Provide a period of quiescence during which suspended waste material settles to the bottom of the tank and is scraped into a hopper and pumped out for disposal. During this period, floatable solids (fats, oils) rise to the surface of te tank and are skimmed off into scum pipes for disposal.
Selective Ion Exchange
The use of a selective ion exchange medium with the property of removing specific ions from a solution.
Able to allow certain size material to pass through while rejecting other size material.A reverse osmosis unit uses a semipermeable membrane.
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.
Largely the water supply of a community after it has been fouled by various uses. From the standpoint of course, it may be a combination of the liquid or water-carried wastes from residences, business buildings, and institutions, together with those from industrial establishments, and with such ground water, surface water, and storm water as may be present.
A system of pipes used for collecting domestic and industrial waste, as well as storm water run-off. Lateral sewers connect homes and industries to trunk sewers, which channel waste into interceptor sewers carry only domestic and industrial wastewater. Storm sewers carry only storm water run-off. Combined sewers carry both.
Siliceous Gel Zeolite
A synthetic, inorganic exchanger produced by the aqueous reaction of alkali with aluminum salts.
Silt Density Index
A measurement of silt, colloids, bacteria and other foulants of Reverse Osmosis (RO) membranes. SDI is used to help determine the suitability of water or other liquids for the RO process.
The accumulated suspended solids of sewage deposited in tanks or basins.
Sludge Age
In the activated sludge process, a measure of the length of time a particle of suspended solids has been undergoing aeration, expressed in day. It is usually computed by dividing the weight of the suspended solids in the aeration tank by the weight of excess activated sludge discharged from the system per day.
Sludge Digestion
The purpose of sludge digestion is to separate the liquid from the solids to facilitate drying. The proper pH range for digested sludge is 6.8 – 7.2.
Sludge Index
Properly called sludge volume index (SVI). It is the volume in millimeters occupied by 1 g of activated sludge after settling of the aerated liquid for 30 minutes.
Sludge Judge
A clear tubular device used to measure sludge depth in clarifiers or other tanks.
Sludge Reaeration
The continuous aeration of sludge after initial aeration for the purpose of improving or maintaining its condition.
A dispersion of stone particles in a liquid carrier during the cutting, grinding, shaping, and polishing processes.
Soda Ash
Chemical used to raise pH and total alkalinity (sodium carbonate).
Sodium Bisulfate
Chemical used to lower pH and total alkalinity (dry acid).
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.
Soft Water
Water containing less than 17 PPM calcium or magnesium.
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.
Dissolved particles in a solvent.
The liquid, such as water, in which other materials (solutes) are dissolved.
Splitter Box
A division box that splits the incoming flow into two or more streams. A device for splitting and directing discharge from the head box to two separate points of application.
See Cyanuric Acid.
A yellowish solid chemical element. The term is also used as a slang expression to refer to water containing hydrogen sulfide gas (H2 S).
Application of large dosages of chlorine to destroy build-up of undesirable compoundsin water.
Compounds that lower the surface tension (or interfacial tension) between two liquids or between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants.
Suspended Solids
Solids physically suspended in sewage that can be removed by proper laboratory filtering.
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.


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.
A toxic volatile organic chemical typically used as an industrial solvent.
The abbreviation for “total dissolved solids”.
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.
Tertiary Waste Treatment
Following secondary treatment, the clarified effluent may require additional aeration and/or other chemical treatment to destroy bacteria remaining from the secondary treating stage, and to increase the content of dissolved oxygen needed for oxidation of the residual BOD. Tertiary treatment can also be used to remove nitrogen and phosphorous. This is done with clorination and often times UV treatment.
Thin-film Composite Membrane
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.
A method of testing by adding a reagent of known strength to a water sample until a specificcolor change indicates the completion of the reaction.
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
A measure of the acid neutralizing capacity of water which indicates its buffering ability,i.e., measure of its resistance to a change in pH. Generally, the higher the total alkalinity, the greater the resistanceto pH change.
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 accumulated total of all solids that might be dissolved in water.
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 total amount of solids in solution and suspension.
Trickling Filter
An aerobic biological process used as secondary treatment of sewage. Effluent from the primary clarifier is distributed over a bed of rocks. As the liquid trickles over the rocks, a biological growth on the rocks breaks down the organic matter in the sewage. The effluent is then taken to a clarifier to remove biological matter coming from the filter.
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.


Ultra Filtration
Is a type of membrane filtration that separates suspended solids and solutes of high molecular from a liquid and low molecular weight solutes. This separation process is used in industry processes, water treatment and research for purifying and concentrating macromolecular solutions.
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 Disinfection
The use of ultraviolet light to destroy bacteria.
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.


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.
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.
Volatile Organic Compounds
Synthetic organic chemicals that vaporize at relatively low temperatures.


Waste Activated Sludge
That portion of sludge from the secondary clarifier in the activated sludge process that is wasted to avoid a buildup of solids in the system.
Waste Treatment Sludge
A series of tanks, screens, filters, and other processes by which most pollutants are removed from water.
Domestic wastewater is 99.9% water and 0.1% solids. Fresh wastewater is usually slightly alkaline. If the pH of the raw wastewater is 8.0, it indicates that the sample is alkaline. If wastewater has a pH value of 6.5, it means that it is acid. Wastewater is said to be septic when it is undergoing decomposition.
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 Pollution
A general term signifying the introduction into water of micro-organisms, chemicals, wastes, or sewage which renders the water unfit for it’s intended use.
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.


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



Naturally occurring or synthetic hydrated sodium alumina silicate with ion exchange properties. Zeolites have been largely replaced with synthetic organic cation ion exchange resins.
Zero Soft
Water with a total hardness less than 1.0 grain per US Gallon (17.1 ppm), as calcium carbonate.