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Water Glossary


A&I— Alternative and Innovative (Wastewater Treatment System)
AA— Accountable Area; Adverse Action; Advices of Allowance; Assistant Administrator; Associate Administrator; Atomic Absorption
AAEE— American Academy of Environmental Engineers
AANWR— Alaskan Arctic National Wildlife Refuge
AAP— Asbestos Action Program
AAPCO— American Association of Pesticide Control Officials
AARC— Alliance for Acid Rain Control 
ABEL— EPA’s computer model for analyzing a violator’s ability to pay a civil penalty.
ABES— Alliance for Balanced Environmental Solutions 
AC— Actual Commitment. Advisory Circular
A&C— Abatement and Control
ACA— American Conservation Association 
ACBM— Asbestos-Containing Building Material
ACE— Alliance for Clean Energy
ACE— Any Credible Evidence
ACEEE— American Council for an Energy Efficient Economy
ACFM— Actual Cubic Feet Per Minute
ACL— Alternate Concentration Limit. Analytical Chemistry Laboratory
ACM— Asbestos-Containing Material
ACP— Agriculture Control Program (Water Quality Management); ACP— Air Carcinogen Policy
ACQUIRE— Aquatic Information Retrieval
ACQR— Air Quality Control Region 
ACS— American Chemical Society 
ACT— Action 
ACTS— Asbestos Contractor Tracking System 
ACWA— American Clean Water Association 
ACWM— Asbestos-Containing Waste Material 
ADABA— Acceptable Data Base
ADB— Applications Data Base
ADI— Acceptable Daily Intake
ADP— AHERA Designated Person; Automated Data Processing
ADQ— Audits of Data Quality
ADR— Alternate Dispute Resolution 
ADSS— Air Data Screening System
ADT— Average Daily Traffic
AEA— Atomic Energy Act
AEC— Associate Enforcement Counsels
AEE— Alliance for Environmental Education
AEERL— Air and Energy Engineering Research Laboratory 
AEM— Acoustic Emission Monitoring
AERE— Association of Environmental and Resource Economists
AES— Auger Electron Spectrometry
AFA— American Forestry Association
AFCA— Area Fuel Consumption Allocation
AFCEE—Air Force Center for Environmental Excellence
AFS— AIRS Facility Subsystem
AFUG— AIRS Facility Users Group 
AH— Allowance Holders 
AHERA— Asbestos Hazard Emergency Response Act 
AHU— Air Handling Unit 
AI— Active Ingredient 
AIC— Active to Inert Conversion 
AICUZ— Air Installation Compatible Use Zones 
AID— Agency for International Development 
AIHC— American Industrial Health Council 
AIP— Auto Ignition Point 
AIRMON— Atmospheric Integrated Research Monitoring Network 
AIRS— Aerometric Information Retrieval System 
AL— Acceptable Level 
ALA— Delta-Aminolevulinic Acid 
ALA-O— Delta-Aminolevulinic Acid Dehydrates 
ALAPO— Association of Local Air Pollution Control Officers 
ALARA— As Low As Reasonably Achievable 
ALC— Application Limiting Constituent 
ALJ— Administrative Law Judge 
ALMS— Atomic Line Molecular Spectroscopy 
ALR— Action Leakage Rate 
AMBIENS— Atmospheric Mass Balance of Industrially Emitted and Natural Sulfur 
AMOS— Air Management Oversight System 
AMPS— Automatic Mapping and Planning System 
AMSA— Association of Metropolitan Sewer Agencies 
ANC— Acid Neutralizing Capacity 
ANPR— Advance Notice of Proposed Rulemaking 
ANRHRD— Air, Noise, & Radiation Health Research Division/ORD 
ANSS— American Nature Study Society 
AOAC— Association of Official Analytical Chemists 
AOC— Abnormal Operating Conditions 
AOD— Argon-Oxygen Decarbonization 
AOML— Atlantic Oceanographic and Meteorological Laboratory 
AP— Accounting Point 
APA— Administrative Procedures Act 
APCA— Air Pollution Control Association 
APCD— Air Pollution Control District 
APDS— Automated Procurement Documentation System 
APHA— American Public Health Association 
APRAC— Urban Diffusion Model for Carbon Monoxide from Motor Vehicle Traffic 
APTI— Air Pollution Training Institute 
APWA— American Public Works Association 
AQ-7— Non-reactive Pollutant Modelling 
AQCCT— Air-Quality Criteria and Control Techniques 
AQCP— Air Quality Control Program 
AQCR— Air-Quality Control Region 
AQD— Air-Quality Digest 
AQDHS— Air-Quality Data Handling System 
AQDM— Air-Quality Display Model 
AQMA— Air-Quality Maintenance Area 
AQMD— Air Quality Management District 
AQMP— Air-Quality Maintenance Plan; Air-Quality Management Plan 
AQSM— Air-Quality Simulation Model 
AQTAD— Air-Quality Technical Assistance Demonstration 
AR— Administrative Record 
A&R— Air and Radiation 
ARA— Assistant Regional Administrator; Associate Regional Administrator 
ARAC— Acid Rain Advisory Committee 
ARAR— Applicable or Relevant and Appropriate Standards, Limitations, Criteria, and Requirements 
ARB— Air Resources Board 
ARC— Agency Ranking Committee 
ARCC— American Rivers Conservation Council 
ARCS— Alternative Remedial Contract Strategy 
ARG— American Resources Group 
ARIP— Accidental Release Information Program 
ARL— Air Resources Laboratory 
ARM— Air Resources Management 
ARNEWS— Acid Rain National Early Warning Systems 
ARO— Alternate Regulatory Option 
ARRP— Acid Rain Research Program 
ARRPA— Air Resources Regional Pollution Assessment Model 
ARS— Agricultural Research Service 
ARZ— Auto Restricted Zone 
AS— Area Source 
ASC— Area Source Category 
ASDWA— Association of State Drinking Water Administrators 
ASHAA— Asbestos in Schools Hazard Abatement Act 
ASHRAE— American Society of Heating, Refrigerating, and Air-Conditioning Engineers 
ASIWCPA— Association of State and Interstate Water Pollution Control Administrators 
ASMDHS— Airshed Model Data Handling System 
ASRL— Atmospheric Sciences Research Laboratory 
AST— Advanced Secondary (Wastewater) Treatment 
ASTHO— Association of State and Territorial Health Officers 
ASTM— American Society for Testing and Materials 
ASTSWMO— Association of State and Territorial Solid Waste Management Officials 
AT— Advanced Treatment. Alpha Track Detection 
ATERIS— Air Toxics Exposure and Risk Information System 
ATS— Action Tracking System; Allowance Tracking System 
ATSDR— Agency for Toxic Substances and Disease Registry 
ATTF— Air Toxics Task Force 
AUSM— Advanced Utility Simulation Model 
A/WPR— Air/Water Pollution Report 
AWRA— American Water Resources Association 
AWT— Advanced Wastewater Treatment 
AWWA— American Water Works Association 
AWWARF— American Water Works Association Research Foundation.

ABSOLUTE FILTER RATING: Filter rating meaning that 99.9 percent of essentially all of the particles larger than a specified micron rating will be trapped on or within the filter.

ABSORPTION: The process of substance actually penetrating into the structure of another substance. This is different from adsorption in which one substances adheres to the surface of another.

Acid Neutralizing Capacity— Measure of ability of a base (e.g. water or soil) to resist changes in pH.

ACIDIC: The condition of water or soil which contains a sufficient amount of acid substances to lower the pH below 7.0.


1. Regulatory levels recommended by EPA for enforcement by FDA and USDA when pesticide residues occur in food or feed commodities for reasons other than the direct application of the pesticide. As opposed to "tolerances” which are established for residues occurring as a direct result of proper usage, action levels are set for inadvertent residues resulting from previous legal use or accidental contamination.

2. In the Superfund program, the existence of a contaminant concentration in the environment high enough to warrant action or trigger a response under SARA and the National Oil and Hazardous Substances Contingency Plan. The term is also used in other regulatory programs.

ACTIVATED CARBON: A form of elemental carbon whose particles have large surface area with adsorptive qualities, primarily used to remove chlorine, objectionable tastes and odors and numerous toxic organic compounds from water. Produced by heating carbonaceous substances, bituminous coal or cellulose-based substances such as wood or coconut shell, to 700 degrees Centigrade or less in the absence of air to form a carbonized char and then activating or oxidizing at 800 to 1000 degrees Centigrade with oxidizing gases such as carbon dioxide or steam to form pores, thus creating a highly porous adsorbent material.

ACTIVATED CARBON BLOCK: a blend of fine activated carbon, water and a suitable binders(such as polyethylene or similar material) that is mixed and molded and hardened or extruded to a cartridge filter of any size and shape. Occasionally specialized media are added along with activated carbon to provide customized performances of specific contaminants such as lead.

ACTIVATOR: A chemical added to a pesticide to increase its activity.

ACTIVE INGREDIENT: In any pesticide product, the component that kills, or otherwise controls, target pests. Pesticides are regulated primarily on the basis of active ingredients.

ACUTE EXPOSURE: A single exposure to a toxic substance which may result in severe biological harm or death. Acute exposures are usually characterized as lasting no longer than a day, as compared to longer, continuing exposure over a period of time.

ACUTE TOXICITY: The ability of a substance to cause severe biological harm or death soon after a single exposure or dose. Also, any poisonous effect resulting from a single short-term exposure to a toxic substance.

ADSORPTION: Removal of a pollutant from air or water by collecting the pollutant on the surface of a solid material; e.g., an advanced method of treating waste in which activated carbon removes organic matter from waste-water.

ADVANCED TREATMENT: A level of wastewater treatment more stringent than secondary treatment; requires an 85-percent reduction in conventional pollutant concentration or a significant reduction in non-conventional pollutants. Sometimes called tertiary treatment.

ADVANCED WASTEWATER TREATMENT: Any treatment of sewage that goes beyond the secondary or biological water treatment stage and includes the removal of nutrients such as phosphorus and nitrogen and a high percentage of suspended solids.

AERATION: A process which promotes biological degradation of organic matter in water. The process may be passive (as when waste is exposed to air), or active (as when a mixing or bubbling device introduces the air). Iron, manganese, etc are targets of this process.

AERATION TANK: A chamber used to inject air into water.

AEROBIC: Life or processes that require, or are not destroyed by, the presence of oxygen.

AEROBIC TREATMENT: Process by which microbes decompose complex organic compounds in the presence of oxygen and use the liberated energy for reproduction and growth. (Such processes include extended aeration, trickling filtration, and rotating biological contactors.)

AIR BINDING: Situation where air enters the filter media and harms both the filtration and backwash processes.

AIR CHANGES PER HOUR(ACH): The movement of a volume of air in a given period of time; if a bottling cleanroom, for example, has one air change per hour, it means that the air in the cleanroom will be replaced in a one-hour period.

AIR GAP: Open vertical gap or empty space that separates drinking water supply to be protected from another water system in a treatment plant or other location. The open gap protects the drinking water from contamination by backflow or back siphonage. Commonly found in home-use reverse osmosis systems.

AIR SPARGING: Injecting air or oxygen into an aquifer to strip or flush volatile contaminants as air bubbles up through The ground water and is captured by a vapor extraction system.

AIR STRIPPING: A treatment system that removes volatile organic compounds (VOCs) from contaminated ground water or surface water by forcing an airstream through the water and causing the compounds to evaporate.

ALGAE: Simple rootless plants that grow in sunlit waters in proportion to the amount of available nutrients. They can affect water quality adversely by lowering the dissolved oxygen in the water. They are food for fish and small aquatic animals.

ALGAL BLOOMS: Sudden spurts of algal growth, which can affect water quality adversely and indicate potentially hazardous changes in local water chemistry.

ALGICIDE: Substance or chemical used specifically to kill or control algae.

ALIQUOT: A measured portion of a sample taken for analysis. One or more aliquots make up a sample. 

ALKALINITY: A measurement of the quantity of chemicals present in water which can neutralize acids. These include carbon dioxide, bicarbonate, carbonate and hydroxides. pH conditions which exceed 7.0.

ALUM: See aluminum sulfate.

ALUMINUM SULFATE: An aluminum salt commonly used as a flocculent by municipal water treatment facilities.

AMPHOTERIC: A substance, such as aluminum, capable of acting as either an acid or base.

ANAEROBIC: A condition in which there is no air or no available free oxygen. Sometimes relates to microbes which can exist without oxygen.

ANIONS: See ion.

AQUIFER: Any geological formation containing water; one that supplies water for wells, springs, etc.


BAA— Board of Assistance Appeals 
BAC— Bioremediation Action Committee; Biotechnology Advisory Committee 
BACM— Best Available Control Measures 
BACT— Best Available Control Technology 
BADT— Best Available Demonstrated Technology 
BAF— Bioaccumulation Factor 
BaP— Benzo(a)Pyrene 
BAP— Benefits Analysis Program 
BART— Best Available Retrofit Technology 
BASIS— Battelle’s Automated Search Information System 
BAT— Best Available Technology 
BATEA— Best Available Treatment Economically Achievable 
BCT— Best Control Technology 
BCPCT— Best Conventional Pollutant Control Technology 
BDAT— Best Demonstrated Achievable Technology 
BDCT— Best Demonstrated Control Technology 
BDT— Best Demonstrated Technology 
BEJ— Best Engineering Judgement. Best Expert Judgment 
BF— Bonafide Notice of Intent to Manufacture or Import (IMD/OTS) 
BID— Background Information Document. Buoyancy Induced Dispersion 
BIOPLUME— Model to Predict the Maximum Extent of Existing Plumes 
BMP— Best Management Practice(s) 
BMR— Baseline Monitoring Report 
BO— Budget Obligations 
BOA— Basic Ordering Agreement (Contracts) 
BOD— Biochemical Oxygen Demand. Biological Oxygen Demand 
BOF— Basic Oxygen Furnace 
BOP— Basic Oxygen Process 
BOPF— Basic Oxygen Process Furnace 
BOYSNC— Beginning of Year Significant Non-Compliers 
BP— Boiling Point 
BPJ— Best Professional Judgment 
BPT— Best Practicable Technology. Pest Practicable Treatment 
BPWTT— Best Practical Wastewater Treatment Technology 
BRI— Building-Related Illness 
BRS— Bibliographic Retrieval Service 
BSI— British Standards Institute 
BSO— Benzene Soluble Organics 
BTZ— Below the Treatment Zone 
BUN— Blood Urea Nitrogen

BACKWASH: Reverse of a solution's flow through a system(i.e. water softener). Often used as a cleansing mechanism in sand and dual media filters.

BACTERIA: Any of a class of microscopic plants having round, rod-like spiral or filamentous single cell or noncellular bodies, often aggregated into colonies or mobile by means of flagella. Living in soil, water, organic matter or the bodies of plants and animals and being autotrophic(self-generative), saprophytic(digests chemicals already in their environment) or parasitic.

BACTERICIDE: Material capable of inhibiting or destroying bacteria. Function is known as bactericidal.

BACTERIOSTATIC: Material capable of reducing the rate of bacterial growth. Sometimes confused with bactericidal.

BINDERS: When used in reference to cartridge filters, refers to chemicals used to hold, or bind, short fibers together in a filter. Also may refer to various chemicals used to bind polymeric compounds in products such as plastic bottles.

BIOFILM: An aggregation of active, multi-layered microbes found on surfaces and in particular inside tubing and pipes. May be difficult to remove by chemical means due to multiple layers and lack of fluid dynamics at surfaces where it resides.

BLINDING: The fouling or plugging of pores in a membrane, usually by a gel-like substance.

BOD: Biochemical oxygen demand.

BRACKISH WATER: Water containing between 1000 and 15000 mg/l of dissolved solids is generally considered to be brackish.

BREAKTHROUGH: The first appearance in the effluent of an adsorbate of interest under specified conditions.

BRIDGING(OR SALT BRIDGING): The caking of salts in a dry water softener tank which causes failure of the liquid or brine beneath the dry salt to become saturated. The net result of bridging is insufficient salt to properly regenerate the resin.

BRINE (same as Reject Water): One of two streams of fluids generated by a Distiller or Reverse Osmosis unit. It contains the impurities removed from the feed water. Characteristically 30,000 to 300,000 ppm.


CARCINOGEN: Any substance which tends to produce cancer in an organism.

CATIONS: See ion.

CELLULASE: An enzyme which causes the decomposition of cellulose.

CELLULOSE ACETATE: A synthetic polymer derived from naturally occurring cellulose and widely used in the fabrication of membranes. The polymers used for reverse osmosis membranes may be diacetate, triacetate or blends of these materials.

CENTRIFUGAL PUMP: A pump containing a rotation impeller or rotating vanes mounted on a shaft in a casing and turned by a power source. The rotating impeller uses centrifugal force to deliver water in a steady steam.

CENTRIFUGE: A mechanical device that uses centrifugal or rotational forces to separate solids from liquids.

CHANNELING: The greater flow of liquid through passages of lower resistance which can occur in fixed beds or columns of particles(carbon, birm, etc.) due to non-uniform packing, irregular sizes and shapes of the particles, gas pockets, wall effects and other causes.

CHLORAMINES: Chemical complexes formed from the reaction between ammonia and chlorine. They are presently being used to disinfect municipal water supplies because unlike chlorine, they don't combine with organics in the water to form potentially dangerous carcinogens such as trihalomethanes (THM). Retains its bactericidal qualities for a longer time than does free chlorine. Chloramines can exist in three forms, the proportions of which depend on the physical and chemical properties of the water: Monochloramine; Dichloramine; Nitrogen Trichloride. Water containing chloramines must not be used for fish or kidney dialysis applications.

CHLORINE: A very toxic biocide. A halogen element isolated as a heavy irritating greenish-yellow gas of pungent odor used especially as a bleach, oxidizing agent and a disinfectant in water purification.

CHLORINATED HYDROCARBONS: A group of organic chemicals formed by reacting petroleum derived chemicals with chlorine. Such chemicals include pesticides (insecticides) and herbicides and are frequently potent carcinogens.

COAGULANT: A chemical which causes dispersed colloidal particles to become destabilized, thereby aiding in their removal during municipal water treatment. Aluminum and iron salts are commonly used for this purpose.

COAGULATION: A practice common in municipal water treatment in which a chemical (coagulant), most commonly alum, is added to water in order to destabilize colloidal particles by neutralization of their electrical charges. Coagulation is used, together with flocculation, as a process for colloid removal.

COD: Chemical oxygen demand

COLLOIDAL MINERAL/COLLOID: Undissolved, sub micron-sized suspended particles which are well dispersed in a solution and will not readily settle out on standing. Most colloidal minerals are held in suspension by their tiny size and/or a static electrical charge. Many colloidal minerals claim to be organic due to the fact that they come from prehistoric mineral deposits such as humic shale and that some of the minerals are bound to carbon.

COMPACTION: The undesirable physical compression of a reverse osmosis or ultrafiltration membrane which results in reduced flux rates. The phenomenon is accelerated at higher temperatures and pressures.

CONCENTRATE: The portion of a feed stream that retains the ions, organics and suspended particles that were rejected during the cross flow filtration or purification process. Associated with water cooled distillers and reverse osmosis systems.

CONDENSATE: Water obtained through distillation by evaporation and subsequent condensation.

CONDUCTIVITY: A measure of the ability of an aqueous substance to transmit an electric current. The conductivity imparted to water by dissolved solids is a function of both the amount and composition of the salts and the temperature of the water.

DEIONIZATION: Removal of ions from water by exchange with other ions associated with fixed charges on a resin. 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. This process is also called demineralization by ion exchange.

DEMINERALIZATION: The process of removing minerals from water e.g. deionization, reverse osmosis and distillation.

DESALINATION: The removal of dissolved inorganic solids(salts) from a solution such as water to produce a liquid which is free of dissolved salts. Desalination is typically accomplished by distillation, reverse osmosis or electrodialysis. A common source water may be seawater.

DIALYSIS DEMENTIA: A severe, often fatal encephalopathy which has been attributed to accumulation in the brain of aluminum from dialysate prepared with inadequately purified water. May include consumption of tap water with high levels of alum used in most municipal water treatment processes.

DISINFECTION: A process for the destruction of bacteria. The process may be physical, as with heat or ultraviolet irradiation, or chemical, as with chlorination.

DISSOLVED SOLIDS(ALSO TOTAL DISSOLVED SOLIDS-TDS): Includes colloidal and suspended particles at sizes far less than one micron in diameter. Associated with evaporation process such as distillation.

DISTILLATION: Steam from boiling water is condensed on a cool surface, collected and stored. Most contaminants do not vaporize and therefore do not pass to the condensate. Removes nearly 100 percent of salts and those organics that do not have a vaporizing temperature near or below that of water. Usually combined with carbon filtration to remove balance of remaining organics with vaporization temperatures below that of water.

DISTILLED WATER: Water which has been purified by passing through an evaporation, condensation cycle; it generally contains less than 5 ppm of dissolved solids.

EFFLUENT: The output stream exiting the system - often the waste stream.

EMPTY BED CONTACT TIME: A measurement of the duration of contact between water and the media through which it is flowing, typically used in reference to carbon beds.

ENDOTOXIN: Bacterial lipopolysaccharide, a substance released from the cell walls of gram-negative bacteria when the organism is broken down.

FERRIC IRON: Small solid iron particles containing trivalent iron, usually as gelatinous ferric hydroxide or ferric oxide, which are suspended in water and visible as "rusty water". Ferric iron can normally be removed by filtration. Also called "precipitated iron".

FERROUS IRON: A divalent iron ion, usually as ferrous bicarbonate which, when dissolved in water, produces a clear solution. It is usually removed by cation exchange water softening. Also called "clear water" iron.

FEED WATER: Water under pressure entering a purification system or an individual piece of purification equipment, such as an ultra filter, distiller or reverse osmosis system.

FILTRATE: The portion of the feed stream that has passed through the membrane or filtering media.

FLOCCULENT: Chemical which, when added to water, causes particles to coagulate into larger, settle able groupings. Aluminum compounds are common catalysts in this process.

FLOW VELOCITY: A quantitative expression of the rate of linear motion at which water passes through a pipe or conduit.

FLUIDIZATION: A process by which particles are suspended by an upward flow of liquid, such as may occur during back washing of ion exchange resin or carbon media.

FLUORIDE: A salt of hydrofluoric acid which may occur naturally in water supplies or be added by municipal processes for the prevention of dental caries. Fluoride is considered toxic in most medical settings and has been implicated with a wide range of physiological disorders including renal bone disease.

FLUX/FLUX RATE: The rate per unit of area at which water passes through a semi-permeable membrane, such as those used for ultrafiltration or reverse osmosis.

FOULING: The deposition of insoluble materials, such as bacteria, colloids, oxides and water-borne debris, onto the surface of a media such as water softening resins, reverse osmosis or ultrafiltration membrane. Fouling is associated with decreased flux rates and may also reduce the rejection rates of reverse osmosis membranes.

FULVIC ACIDS: Acidic substances which are found in humic (organic) soils and which may become suspended in water. A component in the production of chloramines.

FUNGUS: A parasitic plant which produces no chlorophyll and is dependent on other life forms for its existence.

GLAUCONITE SAND: A mineral which is frequently used in depth filters.

GPD: gallons per day.

GPG: grains per gallon. Equivalent to 17.1 milligrams/liter of calcium carbonate.

HARDNESS: The amount of calcium and magnesium in the water in grains per gallon, (expressed as calcium carbonate). This level is important to control during distillation or reverse osmosis processes to prevent scaling. Each grain is equal to 17.1 ppm of calcium and magnesium (expressed as calcium carbonate).

What constitutes truly "hard" water is subject to much debate and controversy. Proponents of water softening systems tend to call water "hard" which contains between 3 and 10 grains of hardness. Unfortunately, this definition is supported by the American Society of Agricultural Engineers and the Water Quality Association, major supporters of the water softening industry.

Water with 10 grains of hardness is regularly used by consumers with little or no adverse affect on plumbing or other household functions. Water which approaches 15 to 20 grains is more in line with situations which require water softening or conditioning. Water with 3 grains of hardness and is termed "moderately hard" by these organizations is typically found in surface and spring water sources, far removed from what one would consider hard water sources.

HEAVY METALS: Metals having a high density or specific gravity. A generic term used to classify contaminants such as cadmium, lead and mercury. These contaminants can damage living things even at low concentrations and tend to accumulate n the food chain.


HYDROGEN SULFIDE: A toxic gas that is detectable by a strong "rotten egg" odor. Associated with high levels of bacterial decay. Commonly found together with iron and manganese contaminants.

HYDROLOGIC CYCLE: The term used to describe how water travels through the environment by evaporation, condensation and precipitation. Identical process is observed in steam distillation systems.

HYDROLYSIS: A chemical process resulting from reactions with water; frequently used in reference to the breakdown of polymers.

HYDROPHILIC: Pertaining to a substance which readily absorbs water ("water-loving").

HYDROPHOBIC: Pertaining to a substance which does not readily absorb water ("water-hating").

ION: An atom or molecule having either a positive or negative electrical charge. Positively charged ions are referred to as cations and ions having a negative charge are termed anions.

ION EXCHANGE: A process by which certain ionized chemicals present in water are replaced with other ionized chemicals temporarily attached to resin particles. The exchange process is made only for ions having the same charge.

IRON: A very common element often present in ground water in amounts ranging from 0.01 to 10.0 ppm(mg/l). Iron may be found in three forms: in soluble forms such as in ferrous bicarbonate; bound with a soluble organic compound; or as suspended ferric iron particles. Iron above 0.3 mg/l is objectionable to water because of staining of laundry and plumbing fixtures.

IRON BACTERIA: Bacteria which thrive on iron and are able to actually use ferrous iron(as found in water or steel pipes) in their metabolic processes to incorporate ferric iron in their cell structure and to deposit gelatinous ferric hydroxide iron compounds in their life processes.

LAMINAR: Non turbulent fluid flow. Associated with fluid dynamics and designs of fluid tubing and pipelines.

LANGELIER SATURATION INDEX: A calculated number used to predict the calcium carbonate(CaCO3) stability of a water; whether a water will precipitate, dissolve, or be in equilibrium with, calcium carbonate. It is sometimes erroneously assumed that any water that tends to dissolve calcium carbonate is automatically corrosive.

Langelier saturation index = pH - pH, where pH = actual pH of the water, and pH, = pH at which the water having the same alkalinity and calcium content is just saturated with calcium carbonate.

LIGNIN: A polysaccharide found in the cell walls of plants; a breakdown product of decaying vegetation which may be present in surface water supplies.

MEMBRANES: Thin films constructed of cellulosic or synthetic materials which are designed to provide selective transport of solutes. Widely used for hemodialysis, micro filtration, ultrafiltration and reverse osmosis, membranes may be either homogeneous or asymmetric. Homogeneous membranes have a uniform structure or cross-section while asymmetric membranes have a dense "skin" which overlays a porous substructure.

METHEMOGLOBINEMIA: The presence in blood of methemoglobin, a substance related to normal oxyhemoglobin but having no oxygen-carrying capabilities and induced by exposure of blood to certain toxic chemicals, such as nitrites.

MICRO FILTRATION: The separation or removal from a liquid of particulates and micro-organisms in the size range of 0.1 to 2 microns in diameter.

MICRON: A unit of linear measure. It is one millionth of a meter, or one thousandth of a millimeter. The smallest particle than can be distinguished by the naked eye would be about 40 microns across.

MICRON RATING: A measurement applied to filters or filter media to indicate the particle size at which a substantial percentage of suspended solids above that size will be removed. As used in the water treatment industry standards, this may be an absolute rating or a nominal rating.

MICRO POROUS: In the context of water purification, membranes having an average pore size which is between 0.1 and 1.0 microns in diameter.

MICROWATT-SECONDS PER SQUARE CENTIMETER: A unit of measurement of intensity and retention or contact time in the operation of ultraviolet(U/V) systems.

Mg/l: Milligrams per liter. A measure of concentration of a dissolved substance. A concentration of one mg/l means that one milligram of a substance is dissolved in each liter of water. For practical purposes, this unit is equal to parts per million(ppm) since one liter of water is equal in weight to one million milligrams. Thus, a liter of water containing 10 milligrams of calcium has 10 parts of calcium per one million parts of water or 10 parts per million(10 ppm).

MICROHM: One millionth of an ohm. The unit of measurement for testing the electrical resistance of water to determine its purity. The closer water comes to absolute purity, the greater its resistance to conduction of an electrical current. Absolute pure water has a specific resistance over 18 million ohms(megohms) across one centimeter of water at a temperature of 78 degrees Fahrenheit.

MILLILITERS/MINUTE: A common measurement for the flow rate of small RO systems. Usually measured with a graduate cylinder. One thousandth of a liter per minute. Milliliters/min x.38 = gal/day.

MIXED BED: The intermix of two or more filter or ion exchange products in the same vessel during a service run. The most common use is in ion exchange systems having a 40/60 percent cation to anion resin bed such as that for a deionization polisher system. In filtration, there may be an intermix of two or more media in a single tank with each stratified into separate layers.

MONOVALENT ION: A cation or anion having a single electrical charge.

MTBE:(Methyl Tertiary Butyl Ether): A volatile organic chemical(VOC) used as an octane-enhancing lead substitute and more recently as an oxygenating agent in gasoline to reduce carbon monoxide emissions from automobiles. MTBE is volatile, flammable and highly soluble in water.

During refueling and gasoline production, MTBE is volatilized to the atmosphere where it dissolves into the atmospheric moisture and returns to earth as precipitation, polluting our water supplies. Since MTBE does not adsorb well with organic matter in soils it is easily washed away. In surface water, MTBE volatilizes into the air while in ground water, MTBE persists and moves freely. MTBE occurrences in ground water above 40 ppb have so far been attributed to point source contamination such as underground gasoline tank leaks, overflows, etc.

EPA has tentatively classified MTBE as a potential human carcinogen.

NANOFILTRATION: A membrane treatment process which falls between reverse osmosis and ultrafiltration on the filtration/separation spectrum. The nanofiltration process can pass more water at lower pressure operations than reverse osmosis, can remove particles in the 300 to 1,000 molecular weight range such as humic acid and organic color bodies present in water, and can reject selected(typically polyvalent) salts. Nanofiltration may be used for selective removal of hardness ions in a process known as membrane softening.

NEUTRALIZATION: The addition of either an acid to a base or a base to an acid to produce a more nearly neutral solution. The use of alkaline or basic materials to neutralize acidity of some water is common practice in water processing to prevent corrosion of metallic home plumbing. 

NITRATE: An anion comprised of one nitrogen atom and three oxygen atoms. Nitrates are considered toxic in hemodialysis water and are also harmful to infants when consumed orally.

NOMINAL FILTER RATING: Filter rating indicating the approximate size particle, the majority of which will not pass through the filter. It is generally interpreted as meaning that 85 percent of the particles of the size equal to the nominal filter rating will be retained by the filter.

OPERATING PRESSURE: The manufacturer's specified range of pressure expressed in pounds per square inch(psi) within which a water processing device or water system is designed to function.

OPERATING TEMPERATURE: The manufacturer's recommend feed water or inlet water temperature for a water treatment system.

OSMOSIS: The natural tendency of water to pass through a semipermeable membrane, so as to equalize concentrations on both sides of the membrane.

OSMOTIC PRESSURE: The force (pressure) resulting when two liquids having different solute concentrations are separated by a semi-permeable membrane. For every 100 ppm, an osmotic "back pressure" of 1 psi is generated and this "back pressure" must be overcome in the reverse osmosis process.

OSTEODYSTROPHY: Abnormal bone development which, in renal patients, may be attributed to parathyroid gland dysfunction and is characterized by high serum phosphorus and alkaline phosphates and low serum calcium levels.

OSTEOMALACIA: A softening of bone due to an accumulation of osteoid and reduced mineralization which may cause fractures with minimal stress.

OSTEOPOROSIS: Demineralization of bone which may cause fractures with minimal stress.

OXIDANTS(OXIDIZING AGENTS): Chemicals which provide oxygen and accept an electron in an oxidation-reduction reaction. Free chlorine and chloramines are oxidants which are widely used for disinfection.

OXIDIZING FILTERS: Filters that use a catalytic media, such as managanous oxides or potassium permangenate, to oxidize iron, manganese and other impurities from water.

OZONE: An extremely active oxidizing agent and bacteriocide which consists of three oxygen atoms. It is formed by the action of a high voltage electrical field on oxygen or air(such as occurs during an electrical storm). Some degree of ozone can also be produced by certain types of ultraviolet lamps.

PERMEABLE: Allowing some material to pass through.

PERMEATE: See product water.

PARTS PER MILLION (ppm): The standard measure of total dissolved solids. Parts of dissolved material in one million parts of water. (eg. one pound of mineral salts dissolved in a million pounds of water would be on part per million).

Pascal(Pa): A unit of pressure equal to one newton of force per square meter. One thousand pascals equal one kilopascal(KPa); a kilopascal equals 0.145 pounds per square inch. Alternatively, 1 psi = 6895 Pa = 6.895 kN/sq.m = 0.0703 kg/

PATHOGENS: Micro-organism that can cause disease in other organisms or in humans, animals and plants. They may be bacteria, viruses or parasites and are found in sewage, in runoff from animals and in water used for swimming. Fish and shellfish contaminated by pathogens, or the contaminated water itself, can cause serious illness.

pH: The balance between the strength of the alkaline and acidic compounds in water. At a pH of 7.0 acid strength and alkaline strength are equal, and the water is neutral. Less than 7 is more acidic. Greater than 7 is more alkaline. On a logarithmic scale of 1 to 14, it is the negative logarithm of hydrogen ion concentration.

PHENOLS: Weak aromatic acids which are indicative of industrial pollution of water supplies. When combined with chlorine, they produce an objectionable taste and odor.

POLYAMIDE: A synthetic polymer of the nylon family used in the fabrication of reverse osmosis and ultrafiltration membranes.

POLYMERS: A chemical compound with many repeating structural units.

POLYSULFONE: A synthetic polymer used to fabricate reverse osmosis and ultrafiltration membranes which are characterized by extreme thermal stability and chemical resistance. Popular in dental waterline filtration systems.

POLYVALENT ION: A cation or anion having a multiple electrical charge.

POLYVINYL CHLORIDE: A thermoplastic piping material produced by the polymerization of vinyl chloride.

PORE: An opening in a membrane which allows certain components to pass through, but not others.

POTASSIUM PERMANGANATE: An oxidizing agent commonly used for the regeneration of manganese green sand iron filters and occasionally used as a disinfectant.

PPB: Parts per billion(equivalent to micrograms per liter)

PPM: Parts per million(equivalent to milligrams per liter)

PRESSURE DROP: Sometimes referred to as "delta P", it is the decrease in hydrostatic force (pressure) due to the effects of friction or restrictions on a flowing liquid.

PRESSURE HEAD: The vertical distance(in feet) equal to the pressure(in psi) at a specific point. The pressure head is equal to the pressure in psi times 2.31 ft/psi.

PRIORITY POLLUTANTS: Those pollutants that pose the most serious health hazards determined by the EPA (Environmental Protection Agency).

PRODUCT WATER: The purified water stream from equipment, such as distillation, reverse osmosis and ultra filter units.

PSI: Pounds per square inch(pressure)

PYROLOSIS: A breakdown process which occurs when organic matter is subjected to elevated temperatures.

RADIAL FLOW: The flow pattern in which water flows from the outside of a filter element to the center core. For example, a replaceable particulate or carbon cartridge filter unit.

RECOVERY(PERCENT RECOVERY): A measurement applied to distillation, reverse osmosis and ultrafiltration equipment which characterizes the ratio of product water to feed water flow rates. The measurement is descriptive of distillation reverse osmosis or ultrafiltration equipment as a system and not of individual membrane elements. Expressed as a , recovery is defined as: % Recovery = (Product flow rate/Feed flow rate) x 100.

REGENERATION: Carried out using either an acid or alkali to remove the accumulated cations or anions, respectively from a filtration media. At the same time, the cation exchanger takes on hydrogen ions to restore themselves to the original hydrogen or hydroxide form, respectively.

REJECTION(PERCENT REJECTION): A measure of the ability of a reverse osmosis membrane to remove salts. Expressed as a percentage, rejection is defined as:
Rejection = (l-Product concentration/Feed concentration) x 100.

RESIN: Specially manufactured polymer beads used in the ion exchange process to remove dissolved salts from water.

REVERSE OSMOSIS: A reversal of the natural phenomenon of osmosis brought about by application of hydraulic pressure greater than the osmotic pressure in water (containing dissolved solids) to cause the water molecules to flow through the membrane away from the dissolved substances.

RYZNAR INDEX: A modification of the Langelier index used to calculate the degree of calcium carbonate saturation and to predict the likelihood of scale formation from a water supply.

SALT PASSAGE RATE: A measurement of the passage of salts through a reverse osmosis membrane. Salt passage is related to rejection by: % Salt passage = 100 - % Rejection.

SCALING: Usually used in reference to distillation or reverse osmosis equipment, scaling is the precipitation of sparingly soluble salts, such as calcium carbonate, onto the surface of a distiller boiler or reverse osmosis membrane. Scaling is associated with decreased flux and reduced reverse osmosis rejection rates. Scaling also effects to a slight degree the efficiency of distillation processes.

SEDIMENTATION: The process by which solids are separated from water by gravity and deposited on the bottom of a container or basin.

SEMIPERMEABLE: Descriptive of a material, such as a reverse osmosis or ultrafiltration membrane, which allows the passage of some molecules and prevents the passage of others.

SILT DENSITY INDEX: A measurement of the rate at which a 0.45 ~m filter disc is plugged under standardized test conditions. Silt density index (SDI) determinations are used to estimate the rate at which various water supplies will cause fouling or pluggage of reverse osmosis or ultrafiltration membranes.

SOFT WATER: Water containing less than 1 grain per gallon dissolved calcium and magnesium salts. Definition of where "softness” starts may vary depending on individual viewpoints

SOLUTE: Dissolved particles in a solvent

SORBENT: See adsorption.

SPIRAL WOUND MEMBRANE: The most common practical configuration of membranes for RO systems.

STERILIZATION: A physical or chemical process that reduces the number of organisms to a safe predetermined level (see also disinfection).

SUPERFICIAL VELOCITY: A quantitative expression of the rate of linear motion with which water passes through a vessel used to house particles, such as ion exchange resin or carbon media.

SURGE TANK: A type of pressurized water storage vessel. Surge tanks typically have large areas of stagnation that offer opportunistic bacteria a favorable environment for multiplication. Commonly found in reverse osmosis systems. Requires periodic sanitation to ensure control of bacterial growth.

SUSPENDED SOLIDS: Includes settleable particles less than one micron in diameter.

TANNIN: Any of a group of water soluble, natural organic phenolic compounds that are produced by metabolism in trees and plants and are part of the degradation-resistant fulvic acid materials formed during the decomposition of vegetation.

Tannins occur in water or in almost any location where large quantities of vegetation have decayed. Tannins can impart a faintly yellowish to brown color to water. Tannin molecules tend to form anions in water above pH 6 and can be treated with anion exchange resins. Below pH 5, tannins are better treated with activated carbon.

THIN FILM COMPOSITE: A membrane made with a polyamide based polymer consisting of three layers: a polyester support web, a micro porous polysulfonic inter layer, and an ultrathin barrier coating on the top surface.

TITRATABLE ALKALINITY: The quantity of hydrogen ions (H+) which must be added to a sample of alkaline water in order to establish a condition of neutrality.

TOTAL DISSOLVED SOLIDS: The sum of all ions in a solution, often approximated by means of electrical conductivity or resistivity measurements. Total dissolved solids (TDS) measurements are commonly used to assess distiller and reverse osmosis unit performance.

It is important to note that a test measuring the electrical conductivity of the water sample provides only an estimate of the TDS present, as conductivity is not precisely proportional to the weight of an ion and nonconductive substances cannot be measured by electrical tests.

TOTAL ORGANIC CARBON: A measurement of the total mass of dissolved carbon in a water sample, excluding that originating from carbon dioxide and carbonates.

TOTAL SUSPENDED SOLIDS: The particles which can be removed from a solution by filtration, usually specified as the matter which will not pass through a 0.45 micron pore-diameter filter.

TURBIDITY: A measurement of the amount of suspended solids (colloids) in a solution. Caused by stirred-up sediment, silt, clay, etc. Turbidity blocks light rays and makes the water opaque. Turbidity is measured in nephelometric turbidity units(NTU).

Potable water should not exceed 0.3 NTU. Turbidity cannot be directly equated to suspended solids because white particles reflect more light than dark-colored particles and many small particles will reflect more light than an equivalent large particle.

ULTRA FILTERS: A membrane based filtration system in which the pore sizes range from 0.002 to 0.1 microns.

ULTRAVIOLET(UV) LIGHT: Radiation(light) having a wavelength shorter than 3900 angstroms, the wavelength of visible light and longer than 100 angstroms, the wavelengths of x-rays. This wvelength puts ultraviolet light at the invisible violet end of the light spectrum. UV light is used as a disinfectant. Water treated by ultraviolet light should be free from particulate materials or turbidity so as to prevent micro-organisms from being shielded from the incident UV radiation.

VIRUS: The smallest infectious microorganism, made of RNA or DNA in a protein shell and which grow only in other, living cells. They are 0.004 to 0.1 microns in size and about 100 times smaller than bacteria.

WATER HAMMER: The shock wave or series of waves caused by the resistance of inertia to an abrupt change of water flow through a water piping system. Water hammer may produce an instantaneous pressure many times greater than the normal pressure. For this reason, many building codes now require the installation of a "water hammer arrestor" or accumulation device to absorb shock waves and prevent damage to appliances such as washing machines as well as water treatment components such as reverse osmosis membranes.

WATER SOFTENER: A pressurized water treatment device in which hard water is passed through a bed of cation exchange media for the purpose of exchanging calcium and magnesium ions for sodium or potassium ions, thus producing a "softened" water which is more desirable for laundering, bathing and dish washing. This cation exchange process was originally called zeolite water softening or the Permutit Process. Most modern water softeners use a sulfonated bead form of styrene/divinylbenzene (DVB) cation resin.