*These definitions have been formulated to reflect water treatment.*


absolute A term to describe a retention of particles greater than the specified cartridge rating.

absorption The process to take up (like a sponge) a substance into its physical structure by a physical or a chemical action, but without a chemical reaction. This is the term used to describe activated carbon’s abilities.

acidity The quantitative capacity of water to neutralize an alkali or base.

acid rain Atmospheric precipitation that by adsorption of carbon dioxide, nitrogen and sulphur oxides in the air that has a pH below 5.6.

activated carbon A medium made from heating a carbon based substance such as coconut shells, coal or petroleum in a controlled atmosphere such as steam. This process forms a highly porous structure with an electrochemically active and adsorptive surface. Activated carbon is typically used in water treatment for the control of taste and odour issues and for the reduction of chemical contaminants.

adsorption The process whereby one substance adheres to the surface of another substance.

aeration The process of adding air and water for the purpose of oxidation or mixing of a fluid.

air gap A break in the drain path that prevents a reverse flow of water from the sewer to the water system, whether the driving force is a positive pressure in the sewer or a negative pressure in the water line.

algae Single-celled or multi-celled organisms commonly found in surface water that produce their own food through photosynthesis.

algal bloom An unusual or excessive abundance of algae growth.

alkalinity The quantitative capacity of water to neutralize an acid.

ambient temperature The outside air temperature of the temperature of a given piece of equipment that is operated on a continuous basis.

amoeba Small single–celled animal (or protozoan) widely distributed in fresh and salt waters.

anaerobic An action or process conducted in the absence of oxygen (air) such as the anaerobic digestion of organic matter by bacteria in a septic disposal system.

angstrom A unit of length equalling 10-10 meters, 10-4 microns, 10-8 cm or 4 X 10-9 inches. The symbol for angstrom is Å.

anion A negatively charged ion in an aqueous solution.

AO Advanced oxidation; to a set of chemical treatment procedures designed to remove organic and inorganic materials in water by an oxidation process.

aquifer A natural underground formation where groundwater is stored.

asbestos A fibrous silicate material, mainly calcium magnesium silicate (CaMgSi2O6) that is a known lung carcinogen.

APHA American Public Health Association; is the primary voice for public health advocacy, leading the way to protect all Americans and their communities from preventable, serious health threats and striving to assure community-based health promotion and disease prevention activities and preventive health services are universally accessible in the United States. (http://www.apha.org/)

ASME American Society of Mechanical Engineers; a society that promotes the art, science & practice of mechanical & multidisciplinary engineering and allied sciences around the globe. (http://www.asme.org/)

ASTM American Society of Testing Materials; an organization who sets standards for laboratory and electronic water. (http://www.astm.org/)

axial flow Term to describe the longitudinal flow along a UV reactor.


backflow The flow of water in a pipe or line in a direction that is opposite to its normal flow.

backwash The counter-current flow of water through a filter media or ion exchange bed for the purpose of cleaning and reclassifying the bed after a normal service run.

bacteria Microscopic single-celled organisms which lack defined nuclear membranes and other specialized functional cell parts and reproduce be cell division or spores.

bactericide Any substance or agent that kills bacteria (also known as a germicide).

bacteriostatic having the ability to inhibit bacterial growth without destroying the bacteria. Silver-impregnated carbon would be an example of a bacteriostatic device.

ballast The electric power source to fire and operate a UV lamp. The ballast provides the necessary high starting voltage to fire the lamp and then regulates the voltage for continuous operation.

bank One or more UV modules that the entire flow for a given reactor train must pass through.

bar A unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. The bar is widely used in descriptions of pressure because it is only about 1% smaller than "standard" atmospheric pressure, and is legally recognized in countries of the EU.

bed expansion The effect produce during backwashing where the filter medium or ion exchange resin fluidizes and rises in the tank.

bioassay A biological test used to assess the effectiveness of UV disinfection for the inactivation of microorganisms.

biocide Any substance or medium having the energy to treat microorganisms.

biofilm An accumulation of live and dead microorganisms which adhere to wetted surfaces such as pipes and membranes. Biofilm may promote the further growth of microbiological contaminants and can greatly affect the performance of an RO membrane.

bio-remediation The biological degradation treatment of waste sludge and soils to breakdown organic and hydrocarbons to CO2 and H2O through the selective use of microorganism.

birm The trade name of a special manganese-coated pumicite medium used as an oxidizing catalyst in water treatment.

bi-valent Having a valence of two, commonly referred to as divalent.

BOD Biochemical oxygen demand (BOD) is a measure of the amount of oxygen required by bacteria for the biochemical degradation of organic material in a water sample.

booster pump An RO term used to describe a piece of equipment designed to increase product water yield.

brackish water Waters containing a total dissolved solids content in the range of 1,000 to 5,000 ppm.

brine A term used in RO technology to describe the crossflow water exiting the membrane which transports the more concentrated impurities left behind by the permeate water. May also be called the concentrate or the reject.

bridging Term to describe when particles that are being removed create an arch (or bridge) over individual openings in the filter media (or membrane).

BWA - A Boil Water Advisory (BWA) will be issued by your municipal water provider if the municipal water being provided to your home or business is deemed to be unfit for human consumption. This may be the result of a number of circumstances, however the municipality is informing their customers that at this point-in-time, the water is not safe for drinking, unless treated by some other method such as physically boiling the water for a minimum of 1 minute at a rapid boil. Depending on the exact nature of the BWA, other precautions may need to be taking such as avoiding baths or showers (especially in water ingestion is possible). The municipality will advise when the BWA is over and how to ensure your home’s water supply is made safe.


CA Cellulose acetate is one of the common polymers used to make RO membranes.

capillary tube Term used in RO technology to describe tubing with a very small diameter (usually Teflon) used to control (restrict) the flow of concentrate to the drain.

carbonate hardness Hardness in water caused by bicarbonates and carbonates of calcium and magnesium. Also called temporary hardness.

carbon dioxide A naturally occurring gas (CO2) present in the atmosphere and formed by the decay of organic matter.

carboxylic A term describing a specific acidic group (COOH) that contributes cation exchange ability to some resins.

carcinogen A substance or agent which is known to cause cancer.

cartridge Any removable preformed or pre-packaged component containing a filtering medium. May also be called an element.

caustic soda The common name for sodium hydroxide (NaOH) or lye. Generally used as regenerant for the anion resin in a DI process or for pH adjustment.

cation A positively charged ion in an aqueous solution.

CFU Colony forming unit; used in microbiology as the measure of viable bacterial or fungal numbers in a specific unit volume of liquid. Unlike direct microscopic counts where all cells, dead and living, are counted, CFU measures viable cells. For convenience the results are given as CFU/mL (colony-forming units per milliliter) for liquids, and CFU/g (colony-forming units per gram) for solids.

channeling Refers to the non-standard flow of water throw a filter media whereby the water takes the path of least resistance rather than passing uniformly throughout the filter medium.

check valve A simple mechanical device used to prevent the reverse flow of a fluid.

chelating agent An additive that raises the apparent solubility of a compound in solution and retards its precipitation.

chloramines A form of chlorine disinfectant for municipal water supplies formed by the reaction of ammonia and chlorine. Chloramines are typically used because they do not combine with other organic matter that may be present in the water to form disinfection by-products such as trihalomethanes (THM’s).

chlorination The application of chlorine or chlorine compounds to water for the purpose of disinfection. Can also be sued for chemical oxidation and odour control.

chlorine A gas (Cl2) widely used in the disinfection of drinking water as well as an oxidizing agent for organic matter, iron, manganese and hydrogen sulphide.

clarification Any process or combination of processes whose primary purpose is to reduce the concentration of suspended matter in water.

coagulant   Or flocculants is a chemical which will cause coagulation. Alum is a typical example of a water treatment coagulant.

coagulation The process of adding a chemical which will cause agglomeration (gathering into a mass) of finely divided particles suspended in water into larger particles.

coalescing The gathering together of coagulated colloidal liquid particles into a single continuous phase.

COD Chemical oxygen demand (COD) is a measure of the organic content of a sample that can be oxidized by a strong chemical oxidant.

collimated-bean apparatus A device used in bioassay testing to collimate (make parallel) a source of light.

colloidal matter Extremely fine suspended matter in water that will not settle out over time. Tannins are one example of colloidal matter.

compaction Describes ultrafiltration membranes’ undesirable physical compression resulting in lower flux rates.

compound A chemical combination of two or more elements in definite ratios by weight in which the set of each individual characteristics of each is lost.

concentrate A term used in RO technology to describe the cross flow water exiting the membrane which transports the more concentrated impurities left behind by the permeate water. May also be called the brine or the reject.

concentration The relative content in dissolved material in a solution such as water.

conductivity A measure of the capacity for water to conduct electricity. The units are micromhos per centimetre (micromhos/cm). Conductivity is used to determine the amount of dissolved solids in the water.

conductivity meter An electronic instrument that measures of the capacity for water to conduct electricity.

contact time Term given to the time (usually in minutes) that the water is in direct contact with a treatment medium or device.

contaminant Any undesirable chemical, physical, or microbiological substance or matter present in the water.

corona A visible electric discharge. Oxygen in the air passing through this discharge is converted to ozone.

Corosex The trade name for a magnesia (MgO) pH correction medium.

cross connection A condition whereby there is a direct hydraulic route between the potable (drinking) water and the nonpotable (waste) water.

Crenothrixpolyspora A species of filamentous, non-pathogenic, bacteria that utilizes iron found in water in its metabolism. A form of iron bacteria.

Cryptosporidium A waterborne protozoan organism that forms cysts and causes acute gastrointestinal illness in humans. Cryptosporidium is highly resistant to traditional forms of disinfection such as chlorination. They are 3-6 microns in size and are easily destroyed by UV light.

CTA Or cellulose triacetate is one of the common polymers used to make RO membranes.

cyst A capsule or protective sac produced about themselves by many protozoans as preparation for entering a resting or a specialized reproductive stage.


Dalton The basic measurement unit for molecular weight of dissolved substances.

deaeration The process of removing non-condensable gases form water (typically oxygen). Typically used in boiler applications.

dechlorination The intentional reduction or removal of chlorine disinfectants from a water supply.

degasification The removal of dissolved gases such as carbon dioxide from water by establishing equilibrium between the water and the surrounding air.

deionization (DI) The process of removing all ionized substances (minerals, slats, gases) from water.

delivered ultraviolet dose The dose that is assigned to the UV test reactor based on reactor validation testing. The delivered UV dose is equivalent to that measured with the collimated-beam apparatus for the same degree of inactivation of the target microorganism.

demineralization Describes any process that removes minerals from water

desalination The removal of dissolved inorganic salts from a water to produce a liquid free from dissolved salts. Reverse osmosis or distillation are two forms of a desalination process.

design ultraviolet dose The delivered UV dose is required for a specific log inactivation of the target microorganism. The design UV dose is used for sizing UV disinfection systems.

dewpoint The temperature at which water vapour present in the air begins to condense and dew begins to form.

dialysis A physical separation process dependant on different diffusion rates of solutes across a permeable membrane without pressure.

diatomaceous earth A white, yellow, or light gray siliceous natural earth composed predominately of the remains of diatoms that typically accumulate in lakes and swamps. Used as an absorbent in filter mediums.

differential pressure The difference in pressure at any tow given points.

dipole Anything having two equal but opposite electric charges or magnetic poles.

disinfection the process of cleaning something, in order to destroy bacteria 

disinfection byproducts ompounds formed as a result of a series of complex reactions between disinfectant ad organic compounds.

dissolved solids The weight of matter, including both organic and inorganic matter, in true solution in a stated volume of water.

distillate The water product condensed from vapour during the distillation process.

distillation The process where water is converted into a vapour state by heating. The resulting vapour is collected, cooled and condensed to a liquid state for use.

divalent Having a valence of two.

dose UV dose is the product of UV intensity (total UV energy per unit volume) and residence time (total time the water is in contact with the UV light), expressed by the equation D = I x T. Typically UV dose is expressed in the units mJ/cm² but can also be in microWsec/cm². The conversion between the two is, 1 mJ/cm² equals 1,000 microWsec/cm².

DWS Drinking water system


effluent Typically the outflow of water after it has passed through a treatment system.

electrodialysis A process in which ions are transferred through membranes from a less concentrated to a more concentrated solution as a result of the passage of a direct electric current.

endotoxin A heat-resistant pyrogen (lipopolysaccharide) found in the cell walls of certain disease-producing bacteria.

enteric viruses Viruses found in waterways related to human excretions.

eductor Also called and venturi; is a device placed in a water stream that creates a vacuum to draw an ozone/air mixture form an ozone generator into the water.

eol End of life; term given to the point-in-time where an ultraviolet lamp degrades to a point where it does not provide adequate disinfection and must be replaced. Please note that just because the lamp is illuminated, it does not necessarily mean it is providing any disinfection.

EPA U.S. Environmental Protection Agency; an agency of the federal government of the United States charged with protecting human health and the environment by writing and enforcing regulations based on laws passed by the US Congress. (http://www.epa.gov/)

eutrophic lake A lake containing a high concentration of dissolved nutrient levels, often a shallow lake with periods of oxygen deficiency.

evaporation The process by which a substance is changed from the liquid to the vapour state.

exhaustion Describes the state of an ion exchange system that is no longer capable of use due to the depletion of the initial supply of available exchangeable ions.


faecal matter containing or derived from animal or human waste.

Faecal coliform matter containing or derived from animal or human waste containing one or more of the coliform groups of bacteria.

FDA Food and Drug Administration; an agency of the United States Department of Health and Human services responsible for protecting and promoting public health through the regulation and supervision of food safety, tobacco products, dietary supplements, prescription and other drugs, vaccines, blood transfusions, medical devices, veterinary products and cosmetics. (http://www.fda.gov/)

feed water An RO term used to describe the water entering into an RO membrane. Once passed through the membrane the feed water will be separated into the permeate (product) and the concentrate (reject) water.

ferric iron The insoluble, trivalent form of iron (Fe3+). Ferric iron is usually combined as ferric hydroxide (Fe(OH)3). or as ferric oxide (Fe2O3). This form of iron is usually suspended in water and leads to a rusty colour and can be removed by mechanical filtration.

ferrous iron The soluble (also called clear water iron), divalent form of iron (Fe2+). Ferrous iron is usually combined as ferrous bicarbonate (Fe(HCO3)2). Ferrous iron can be oxidized into ferric iron by the introduction of an oxidant (e.g. chlorine, ozone, etc.) and subsequently filtered out. Small amounts of ferrous iron can also be removed by a water softener.

Filter-Ag The trade name for special aluminum silicate (Pumicite) granular product used as a general filtration medium.

filtrate The effluent liquid from a filter system.

fines Extremely small particles of media (e.g. carbon) that ma be formed during the manufacturing or agitation during transportation. These fines are typically released upon start-up of a cartridge and are considered as a nuisance; however they can potentially clog RO membranes.

floc A flocculent mass formed by the aggregation of a number of fine suspended particles.

flocculant Or coagulant is a chemical which will cause coagulation. Alum is a typical example of a water treatment flocculant.

flocculation The process of bringing together the established or coagulated particles to form larger agglomeration or floc.

flowrate The quantity of liquid that is discharged per unit time relative to a fixed reference point.

fouling factor  The reduction in available UV output due to changes in transmittance of the quartz sleeve separating the UV lamp from the liquid. The reduction in available UV output is determined by comparison to a new unused sleeve.

flux An RO term used to describe the rate of permeate (product) water flow per unit of time per unit area (e.g. gallons per day per square foot).

fouling Term used to describe any type of physical accumulation of particulate and/or organic matter that adheres to a surface (e.g. quartz sleeve or RO membrane) and causes a reduction in efficiency and performance.

free chlorine That portion of the total residual chlorine composed of dissolved chlorine gas (Cl2), hypochlorous acid (HOCl) and hypochlorite ion (OCl). Free chlorine = total chlorine – combined chlorine.

FTU Formazine turbidity units; a measure of turbidity performed by a candle turbidimeter.

fulvic acid A water-soluble, natural organic substance of low molecular weight that is derived from humis often found in surface water. They cast a yellow hue to the water.

fungi Simple one-celled organism, without chlorophyll, often filamentous (includes yeasts and moulds)


GAC Granular activated carbon; the granular form of activated carbon used in water treatment applications.

Gallionella ferruginea A genus of stalked, ribbon-like bacteria that utilizes iron found in water in its metabolism. One of the many types of iron bacteria.

germicidal UV The germicidal range of the electromagnetic spectrum (i.e., wavelengths between 200 and 300 nm).

Giardia lamblia A type of cyst found in the intestines of mammals and in water contaminated by mammal droppings. Sometimes called “Beaver Fever” because beaver droppings containing giardia lamblia are often suspected of contaminating streams and causing the disease in humans from consuming the water. Giardia lamblia cysts are easily destroyed by UV radiation.

GPD Gallons per day

GPG Grains per gallon; a common unit of measurement in Canada and the US for measuring water hardness. One grain per gallon is equivalent to 17.1 mg/L or (ppm) when expressed as CaCO3.

ground fault interrupter A device that measures and trips at low leakage electrical current to ground.

groundwater Water in the saturated zone found under hydrostatic pressure. Body of water beneath the surface of the ground, typically stored in an aquifer.


half-life The time required for half of the substance present at the beginning to dissipate or disintegrate.

halogens A family of elements composed of chlorine, iodine, bromine, fluorine and astatine.

halophilic bacteria Salt-tolerant bacteria often found in solar salt that has not been fully kiln dried or in salt that may have been exposed to unsanitary conditions over a long period of time.

hardness Term used to describe the presence of calcium and magnesium compounds in the water.

headloss Loss of energy caused by friction or turbulence induced by appurtenances in pipes and open channels.

heavy metals Metallic elements with high atomic weights (e.g. mercury, chromium, lead and arsenic). They can damage living things at low concentrations and tend to accumulate in the food chain.

heavy water Water that has hydrogen isotopes in the deuterium form.

haemodialysis The process of purifying a kidney patient’s blood by means of a dialysis machine.

high-purity water Highly treated water with attention to microbiological reduction or elimination. Term is commonly used in the pharmaceutical industry.

HPC Heterotrophic plate count is the level of live, generally non-pathogenic, bacteria in water supplies usually expressed in colony forming units (CFU) per metric volume. Heterotrophic bacteria commonly colonize in most POU water treatment systems and are not considered a health risk to the general population.

humic acid A water-soluble organic compound composed of decayed vegetable matter which is leached into a water source by runoff. Case a brownish hue to the water. Humic acid is found mostly is surface water sources.

hydrocarbon An organic compound containing only carbon and hydrogen often occurs in petroleum products, natural gas, coal, and bitumen’s.

hydrogen ion concentration The concentration of hydrogen ions in moles per litre of solution (often expressed as pH).

hydrogen sulphide A corrosive and flammable gas (H2S) easily identified by its “rotten egg” smell. Often referred to as sulphur water.

hydrologic cycle The complete circuit that water takes in nature including its many forms of precipitation, its journey through, over and into the earth’s surface and its eventual evaporation and return to the atmosphere.

hydrophobic The characteristic of a material or mineral to repel water or fail to absorb water.

hydroxide The ion formed by an oxygen and hydrogen atom. The term used to describe the anionic radical (OH-) that is responsible for the alkalinity of solution.

hydroxyl The univalent group of radical (OH-) consisting of one atom of oxygen and one of hydrogen. Hydroxides include sodium hydroxide (NaOH) which is used as a regenerant for anion exchange units.

hypereutrophic lake Are very nutrient-rich lakes characterized by frequent and severe nuisance algal blooms and low transparency. Hypereutrophic lakes are the most biologically productive lakes, and support large amounts of plants, fish and other animals.


illuminance A measure of photometric flux per unit area, or visible flux density. Illuminance is typically expressed in lux (lumens per square metre) or foot-candles (lumens per square foot).

injector A device through which a gaseous mixture (such as an ozone/air mixture) is fed under pressure into a water stream. The injector provides for mixing and the dissolution of the gas (e.g. ozone) in the water.

iodine number A measure of an activated carbon product to adsorb low molecular weight substances. Iodine number is equal to the mgs of iodine that can be adsorbed on one gram of activated carbon.

ion An atom or group of atoms which carries an electrical charge as a result of having gained or lost electrons in the process of its parent compound dissolving in water.

irradiance A measure of radiometric flux per unit are, or flux density. Irradiance is typically expressed in W/cm² (watts per square centimetre) or W/m2 (watts per square metre).

ion exchange The process whereby ions in solution are interchanged by an insoluble reactive material. A typical water softener is an example of the ion exchange process.

ionization The process in which atoms gain or lose electrons and thus become ions with positive and negative charges.

iron bacteria Micro-organism that thrive on iron and are capable of utilizing ferrous iron in their metabolism and precipitating a gelatinous ferric hydroxide in their sheaths. May also be called organic iron and can be found as Crenothrixpolyspora and Gallionella ferruginea. Iron bacteria cannot be treated by UV alone.

isotope One of two or more atoms or elements that have the same atomic number but that differ in other respects such as atomic weight (e.g., carbon-12 and carbon-14)


JTU Jackson turbidity units; a measure of turbidity performed by a candle turbidimeter


laminar flow Fluid flowing in layers without mixing. The form of flow of a fluid in which the flow paths are in smooth, parallel lines with essentially no mixing and no turbulence.

lamp age factor The reduction in available UV output at the end of UV lamp life as compared to a new lamp, after the appropriate burn-in period.

Langelier saturation index A calculated number used to predict the calcium carbonate (CaCO3) stability of a water; that is, whether a water will precipitate, dissolve, or be in equilibrium with, calcium carbonate.

leachate Water that has percolated through soil or a filter material containing solute substances so that it now contains certain amounts of these substances in solution.

Legionella pneumophlia Also known as Legionnaires’ Disease, a bacteria causing pneumonia-like illness caused by inhalation of legionella bacteria from aerosols produced by circulating cooling tower water, humidifiers, spas, and showers. Thrives at 38°C (100°F) but can be destroyed a temperatures of 77°C (170°F).

log kill The term log kill or more aptly log reduction, refers to the level of reduction that the ultraviolet energy has on a specific organisms in a logarithmic ratio.

LP Term given to a low-pressure mercury vapour lamp used in ultraviolet systems. LP lamps typically have an output of 425 mA.

LP-HO Term given to a low-pressure high-output mercury vapour lamp used in ultraviolet systems. LP-HO lamps typically have an output between 800-1000 mA.


MCL Maximum contaminant level; the highest permissible level of a regulated contaminant allowed under federal law in water delivered to a public water system’s customer (homeowners tap).

membrane An RO term to describe a thin sheet or surface film with semipermeable and microporus characteristics. These two properties will allow water molecules to readily pass through while blocking most dissolved solids, microorganisms, larger organic molecules and virtually all particulate and colloidal matter.

mesotrophic lake Are lakes with an intermediate level of productivity, greater than oligotrophic lakes, but less than eutrophic lakes. These lakes are commonly clear water lakes and ponds with beds of submerged aquatic plants and medium levels of nutrients.

mg/L milligrams per litre; a common measure of concentration of a dissolved substance in water. For practical purposes this unit is interchangeable with parts per million (ppm).

microfiltration (MF) The separation or removal of particulates of more than 0.02μm or less than 10.0 μm in size from liquids or form particulates of other sizes.

micron A metric unit of length defined as one-millionth of a meter (1/25,000 of an inch) Used in water treatment to express the size of waterborne particles ad microorganisms.

microorganism A microscopic animal or vegetable organism not visible to the naked eye.

microwatt An expression of intensity of an ultraviolet system equal to one millionth of a watt.

microwatt-seconds per square centimetre A unit of measurement given to UV dose, expressed as intensity vs. time. The unit, microWsec/cm², has since been replaced with the units millijoules per square centimetre (1 mJ/cm² equals 1,000 microWsec/cm²).

millijoules per square centimetre A unit of measurement given to UV dose, expressed as intensity vs. time. The unit is mJ/cm². 1 mJ/cm² is equivalent to 1,000 microWsec/cm².

mineral salts Common term used to refer to dissolved solids in water.

mixed-bed The term given to the intermix of two or more filter or ion exchange medias in the same pressure vessel during a service run.

module An RO term used to describe an RO element inside a pressure vessel.

mole The molecular weight of a chemical compound expressed in grams.

molecule The smallest particle of an element or compound that retains all of the characteristics of the element or compound. A molecule is made up of one or more atoms.

molecular weight The sum of the atomic weights of the atom in a molecule.

monovalent Having a valence of one.

most probable number Term indicates the number of organism that, according to statistical theory, would be most likely to produce the results observed in certain bacteriological tests.


nanofiltration A membrane treatment process that falls between RO and ultrafiltration and is capable of removing particles in the 300 to 1,000 molecular weight range.

nanometer A unit of length in the metric system equal to one billionth (10-9); one millimicron or 10Å units.

nematode Any roundworm of the phylum Nematoda, having unsegmented thread-like bodies.

nephelometer A device used to measure turbidity units with results expressed in Nephelometric Turbidity Units (NTU).

NIST-traceable Refers to an independent laboratory, national Institute of Standards and Technology in Gaithersburg, MD (http://www.nist.gov/index.html) who independently test and certify the optical properties of a radiometer that is used to calibrate ultraviolet sensors used in UV systems.

nominal A filter rating indicating the approximate minimum size particle capable of being retained to some specific percentage by the filter.

non-carbonate hardness Hardness caused by chlorides, sulphates, and nitrates of calcium and magnesium. Evaporation of waters containing these ions makes the water highly corrosive.

non-pathogenic A substance that does not contain disease causing organisms.

not detectable A term used in water analysis to mean that the substance being tested cannot be detected by the equipment or by the method being used.

NSF NSF International; an independent non-governmental organization who sets a variety of standards, including many for water treatment systems. (http://www.nsf.org/)

NTU Nephelometric turbidity unit; the standard unit of measurement for turbidity in water analysis


off-gas Term given to the undissolved ozonated air given off by an ozone system

oligotrophic lake Are lakes with low primary productivity, the result of a low nutrient content. These lakes have a low algal production, are very clear, and typically have a high drinking water quality. The bottoms of these lakes are extremely rich in oxygen.

operational UV dose The UV dose that is established based on the results of the equipment validation testing. The operational UV dose can be used to make most efficient use of the UV disinfection system while maintaining the design UV dose.

operating pressure The manufacturer’s specified range of pressure for the safe operation of a treatment device.

organics Any compound whose chemical structure is based on carbon.

osmosis The process of diffusion of a solvent through a semi-permeable membrane from a solution of a lower concentration to one of a higher concentration.

osmotic pressure The potential energy of a solution due to dissolved solids (as ions) expressed as pressure (psi).

oxidant Any chemical substance capable of promoting oxidation.

oxidation Any chemical reaction in which electrons are transferred.

oxidize To increase a molecule or ion in positive valence; to lose electrons to an oxidizing agent.

ozone Oxygen in a molecular form with three atoms of oxygen forming each molecule. Ozone (O3) is typically used for disinfection and/or oxidation purposes.


pasteurization A process for the killing of pathogenic microorganism in a liquid by heat applied for a critical period of time.

pathogen Any microorganism or virus that is disease-producing.

pathogenic The capability of causing disease.

particulate matter, exclusive of gases, existing in the non-liquid state that is dispersed in water to give a heterogeneous mixture.

% recovery An RO term used to indicate the percentage of feedwater that passes through the RO membrane as permeate (product water).

% rejection An RO term used to indicate the percentage of feedwater TDS that is prevented from passing through the membrane with the permeate. Percent rejection = (Feed TDS – Permeate TDS)/Feed TDS.

performance validation protocol A procedure whereby the performance of UV equipment is validated.

permeability The ability to pass a liquid under pressure (e.g., RO) or the ability of an ion exchange membrane to pass ions under the influence of an electric current.

permeate An RO term used to describe the portion of the feedwater that passes through the membrane. Also known as product water.

pH An expression of the hydrogen ion concentration designed to measure the acidity or basicidity of an aqueous solution. Specifically it is the reciprocal of the logarithm of the hydrogen ion concentration. The pH scale runs from 0 to 14 where 7 is considered neutral (equal concentrations of both free hydrogen and hydroxide ions). pH values below 7 are considered acidic while ph values above 7 indicate increasing base concentrations.

photodiode A type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation. Photodiodes are used in UV sensors to detect the amount of UV energy given off by the UV light source.

POE Point-of-entry; describes the location a piece of water treatment will typically be installed. POE systems are installed on the main cold water line coming into the house and feed the entire house, including the hot water. POE systems are typically larger than their point-of-use (POU) counterparts.

polymer A chain of organic molecules produced by the joining of primary units called monomers.

pore On opening in a membrane or filter matrix.

porus Material that allows water to pass through.

potable Water fit for human consumption.

POU Point-of-use; describes the location a piece of water treatment will typically be installed. POU systems are installed on a single tap such as the kitchen sink. POU systems are typically smaller than their point-of-entry (POE) counterparts.

ppb Parts per billion, 1 ppb denotes one part per 1,000,000,000 parts, one part in 109, and a value of 1 × 10–9. This is equivalent to one drop of water diluted into 250 chemical drums (50 m³), or about three seconds out of a century.

ppm Parts per million, 1 ppm denotes one part per 1,000,000 parts, one part in 106, and a value of 1 × 10–6. This is equivalent to one drop of water diluted into 50 liters (roughly the fuel tank capacity of a compact car), or about thirty seconds out of a year.

ppt Parts per trillion, 1 ppt denotes one part per 1,000,000,000,000 parts, one part in 1012, and a value of 1 × 10–12. This is equivalent to one drop of water diluted into 20 Olympic-size swimming pools (50,000 m³), or about three seconds out of every hundred thousand years.

precipitate Solid matter separated from a solution or suspension.

precursors Compounds that lead to other compounds.

pressure differential The difference in the pressure between two points in a water system.

pressure drop A decrease in water pressure resulting from the friction of flowing water in pipes and resistance to water flowing through pipes or other water treatment equipment.

primary contaminants A list of heath related contaminants specified by the USEPA with enforceable limits called maximum contaminant level (MCL’s).

protozoan Large, microscopic, single cell organism, higher on the food chain than the bacteria they consume.

psi Pound per square inch or, more accurately, pound-force per square inch (lbf/in2 or lbf/in2) is a unit of pressure or of stress. It is the pressure resulting from a force of one pound-force applied to an area of one square inch. 1 psi approximately equals 6,894.757 Pa, where pascal (Pa) is the SI unit of pressure.

psig Pounds-force per square inch gauge is the pressure relative to the surrounding atmosphere.

pyrogen Organic compounds that cause elevation of body temperature above normal when they get into the bloodstream.


quartz sleeve An outer jacket of quartz glass used to protect a UV lamp.

quartz sleeve fouling The formation of material on the quartz sleeve which causes a reduction in the UV intensity emitted from the quartz sleeve. Typically caused by iron or hardness in the water.

quartz sleeve scaling The formation of a scale on the quartz sleeve that causes a reduction in the UV intensity emitted from inside the quartz sleeve. Scaling is typically caused by the multivalent metallic ions in solution.


radiance A measure of the flux density per unit solid viewing angle, expressed in W/cm²/sr. Radiance is independent of distance for an extended area source, because the sampled are increases with distance, cancelling inverse square losses.

radiant intensity A measure of radiometric power per unit solid angle, expressed in watts per steradian.

radiometer A device for measuring the radiant flux (power) of electromagnetic radiation.

reactor Term given to the chamber (usually stainless steel) of an ultraviolet disinfection system.

regeneration The displacement from the ion exchanger or catalyst medium of the ions removed during the service run and the restoration of the capacity for reuse.

reject A term used in RO technology to describe the crossflow water exiting the membrane which transports the more concentrated impurities left behind by the permeate water. May also be called the concentrate or the brine.

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

resistivity The property of a substance to resist the flow of electricity; the measurement of that resistance.

retenate The concentrate stream discharge from an ultrafiltration system.

reverse osmosis (RO) Is a desalination process for the reduction of dissolved ions from water in which pressure is employed to force water through a semi-permeable membrane, which will transmit the water but reject most other dissolved material.


sanitation A 2-log reduction which translates into a 50-99% reduction in the level of microorganisms in the water (a reduction of 1 out of 100).

scaling The precipitation of dissolved solids (minerals) that are deposited on a surface. Scaling is typically caused by calcium and magnesium due to their limited solubility.

SDI Silt Density Index, a test used to measure the level of suspended solids in feed water for an RO system.

semi-permeable membrane A very thin sheet of fine fibre of specially fabricated material with exceedingly small pore size allowing for the selective passage of substances through its pores. These membranes allow the passage of some substances, but not all.

seprolator A spiral-wound membrane cartridge or element in crossflow membrane systems.

sequestration A chemical reaction in which certain ions are bound into stable, water soluble compound, thus preventing undesirable actions by the ions such as the oxidation of iron.

solarisation The photo-chemical aging of a UV lamp caused by the UV radiation emitted. The intensity of the lamp diminishes with the amount of time the UV lamp is emitting energy.

solutes Matter dissolved in a solvent.

sterilization A 6-log reduction which translates into a 99.9999% reduction in the level of microorganisms in the water (a reduction of 1 out of 1,000,000).

suspended solids The solid particles in water that are not in solution> a measure of undissolved matter determined gravimetrically.


target pathogen The microorganism that is of concern with respect to the protection of public health.

TDS Total dissolved solids; the total weight of solid substances that are dissolved in a unit volume of water most commonly expressed in mg per litre (mg/L) or parts per million (ppm).

TDS creep An RO term describing the natural diffusion of TDS ions through the membrane form the feed side to the permeate side when the feed pressure is shut off.

TFC An abbreviation for Thin Film Composite, a class of membranes fabricated with different materials in the separation and support layers.

thermocouple A junction between two different metals that produces a voltage related to a temperature difference. Thermocouples are a widely used type of temperature sensor and are typically incorporated into UV designs.

THMs Trihalomethanes are a group of suspected carcinogenic organic chemicals formed in water when chlorine, used as a disinfectant, reacts with naturally occurring organic matter such as decayed vegetation (humic acids). Chloroform is one of the most common THM’s formed in this type of reaction.

TOC Total organic carbon; the amount of carbon bound in organic compounds in a water sample as determined by a standard laboratory test.

total chlorine The total concentration of chlorine in water, including both free (e.g., hypochlorous acid) and combined (e.g., chloramines) chlorine

traceability the stringent record keeping on the use and origin of component materials.

TS Total solids; the sum of total dissolved solids and total suspended solids.

TSS Total suspended solids; the residual matter which can be removed from a solution by filtration.

turbidity The amount of small suspended inorganic and/or organic particles measured by the amount of scattering and absorption of light caused by particles. In water treatment, the nephelometric (NTU) is the most common unit and potable waters should not exceed 0.5 NTU.

turbidity units Measurement of the relative ability of a solution to allow a light beam to pass through it


ultrafiltration the separation of one component of a solution from another component by means of pressure and flow exerted on a semi-permeable membrane, with membrane pore sizes ranging from 10Å to 0.2 micron.

ultrapure water Highly treated water of high resistivity and no organics; usually used in the semiconductor and pharmaceutical industries.

ultraviolet absorbance The absorption of UV light is defined by the Beer-Lambert law as when a parallel beam of mono-chromatic radiation, such as 254 nm, passes through a non-diffusing absorbing medium such as water a constant fraction of the radiation is absorbed in each unit distance of the medium traversed.

ultraviolet absorber Substances that absorb radiant energy in the wavelength of ultraviolet.

ultraviolet demand The amount of ultraviolet rays exposure required to inactivate certain microorganisms.

ultraviolet radiation A band of nonionizing electromagnetic radiation having wavelengths from 5 to 400 nm (wavelengths that are effective for microorganism inactivation are in the range from 200 to 300 nm. The most effective range is between 250 and 275, with the optimum being between 260 and 265 nm).

ultraviolet transmittance of fluid (UVT) The ability of a fluid to transmit ultraviolet radiation. Factors known to affect ultraviolet transmittance of a fluid include dissolved organics, dissolved iron, colour, and turbidity. Ultraviolet transmittance is quantified by spectrophometric measurement at a wavelength of 253.7 nm using a 1-cm path length.

ultraviolet 254 absorbance The absorbance of electromagnetic radiation at a wavelength 254 nm buy a liquid through a 1-cm path length.

USP United States Pharmacopeia; is a non-governmental, official public standards-setting authority for the pharmaceutical industry, including water used in pharmaceutical production. (http://www.usp.org/)

UV-A Ultraviolet energy in the 315-400 nanometer wavelength. UV-A is the least harmful and most common found type of UV light because it has the least energy.

UV-B Ultraviolet energy in the 280-315 nanometer wavelength. UV-B is typically the most destructive form of UV light because it has enough energy to damage biological tissues yet not quite enough to be completely absorbed by the atmosphere.

UV-C Ultraviolet energy in the 100-280 nanometer wavelength. UV-C has the shortest wavelength and is almost completely absorbed in air and as a result is almost never observed in nature. It is in this wavelength that the low-pressure mercury vapour lamp emits its spectral output (253.7 nm) and used for disinfection.

UVT UV transmittance is the measurement of a fluids ability to transmit UV light. UVT testing, performed with a spectrophotometer, is required to determine how effective a UV system will be against different types of water.


valence A number indicating the electrical charge of ions. These charges can be both positive (Na+) and negative (Cl-) and can be either monovalent (single charge like Ca+) or divalent (double charge like Fe2+)

validation The mandating of specific testing and record keeping procedures to ensure compliance not only with a specific quality but with a specific means to achieve that quality.

vaporize The process of converting a liquid to a vapour state.

venturi Also called and eductor, is a device placed in a water stream that creates a vacuum to draw an ozone/air mixture form an ozone generator into the water.

virus A parasitic infectious microbe, composed almost entirely of protein and nucleic acids, which can cause disease in humans.

VOC Volatile organic chemical (or compound): organic chemicals that readily vaporize at room temperature and have been detected in public waters as a result of chemical disposal and pollution.

volatile A substance capable of being readily vaporized at relatively low temperatures.


waterborne Supported by or carried by water.

waterborne disease A disease caused by a bacterium or organism able to live in or be carried by water.

water hammer The shock wave or series of waves produced by the abrupt acceleration or deceleration of water flow through a water piping system, caused by inertia.

WFI Water for injection

WHO World Health Organization; is a specialized agency of the United Nations (UN) that acts as a coordinating authority on international public health. (http://www.who.int/en/)