The micron rating of a filter. It indicates that any particle larger than a specific size will be trapped within the filter.



When a solid takes up molecules into its structure.


Acid aerosol

Very small liquid or solid particles that are acidic and are small enough to become airborne.


Acidic water

Acid neutralizing capacity.

Measure of the buffering capacity of water; the ability of water to resist changes in pH.


Acid rain

Rain that has a flamboyantly low pH, due to contact with atmospheric pollutants such as sulphuric oxides.



The quantitative capacity of water to neutralize a base, expressed in ppm or mg/L calcium carbonate equivalent. The number of hydrogen atoms that are present determines this. It is usually measured by titration with a standard solution of sodium hydroxide.


Activated coal

This is the most commonly used adsorption medium, produced by heating carbonaceous substances or cellulose bases in the absence of air. It has a very porous structure and is commonly used to remove organic matter and dissolved gases from water. Its appearance is similar to coal or peat. Available in granular, powder or block form; in powder form it has the highest adsorption capacity.


Activated sludge

Oxygen dependent biological process that serves to convert soluble organic matter to solid biomass, that is removable by gravity or filtration.


Active groups

Really fixed ions bolted on to the matrix of an ion exchanger. Each active group must always have a counter-ion of opposite charge near itself.



Separation of liquids, gases, colloids or suspended matter from a medium by adherence to the surface or pores of a solid. Contaminant reduction by carbon is through adherence (adsorption) of the contaminant and not through absorption.


Advanced oxidation process

One of several combination oxidation processes. Advanced chemical oxidation processes use (chemical) oxidants to reduce COD/BOD levels, and to remove both organic and oxidisable inorganic components. The processes can completely oxidise organic materials to carbon dioxide and water, although it is often not necessary to operate the processes to this level of treatment.


A wide variety of advanced oxidation processes are available:

- Chemical oxidation process using hydrogen peroxide, ozone, combined ozone & peroxide, hypochlorite, Fenton's reagent, etc.

- Ultra-violet (UV) enhanced oxidation such as UV/ ozone, UV/ hydrogen, UV/air

- Wet air oxidation and catalytic wet air oxidation (where air is used as the oxidant)


Advanced Wastewater Treatment

Any treatment of sewage water that includes the removal of nutrients such as phosphorus and nitrogen and a high percentage of suspended solids.



Technique that is used with water treatment that demands oxygen supply, commonly known as aerobic biological water purification. Either water is brought into contact with water droplets by spraying or air is brought into contact with water by means of aeration facilities. Air is pressed through a body of water by bubbling and the water is supplied with oxygen.


Aeration tank

A tank that is used to inject air into water.



A process that takes place in the presence of oxygen, such as the digestion of organic matter by bacteria in an oxidation pond.



Very small liquid or solid particles dispersed in air.



The keenness with which an ion exchanger takes up and holds on to a counter-ion. Affinities are very much affected by the concentration of the electrolyte surrounding the ion exchanger.



A process of bringing smaller particles together to form a larger mass.


Aggressive water

Water that is soft and acidic and can corrode plumbing, pipes and appliances.



Single- or multi-celled organisms that are commonly found in surface water, such as duckweed. They produce their own food through photosynthesis. The algae population is divided up into green algae and blue algae, of which the blue algae are very damageable to human health. Excessive algae growth may cause the water to have undesirable odors or tastes. Decay of algae diminishes oxygen supplies in the water.


Algal blooms

Periods of enlarged algal growths that affect water quality. Algal blooms indicate potentially hazardous changes in the chemistry of water.



Alkalinity means the buffering capacity of water; the capacity of the water to neutralize itself. It prevents the water pH levels from becoming too basic or acid. It also adds carbon to water. Alkalinity stabilizes water at pH levels around 7. However, when the acidity is high in water the alkalinity decreases, which can cause harmful conditions for aquatic life.

In water chemistry alkalinity is expressed in ppm or mg/L of equivalent calcium carbonate. Total alkalinity of water is the sum of all three sorts of alkalinity; carbonate, bicarbonate and hydroxide alkalinity.



Sediments deposited by erosion processes, usually by streams.



A process that takes place in the absence of oxygen, such as the digestion of organic matter by bacteria in a UASB-reactor.



A negatively charged ion that results from the dissociation of salts, acids or alkali's in solution.



A site in electrolysis where metal goes into solution as a cation leaving behind an equivalent of electrons to be transferred to an opposite electrode, called a cathode.



Growing in water, living in water, or frequenting water.



Something made up of water.

Aqueous solubility

The maximum concentration of a chemical that dissolves in a given amount of water.



A layer in the soil that is capable of transporting a significant volume of groundwater.



The ability of water to purify itself of pollutants.


Assimilative Capacity

The capacity of natural water to receive wastewaters or toxic materials without negative effects and without damage to aquatic life or humans who consume the water.



The smallest unit of matter that is unique to a particular element. They are the ultimate building blocks for all matter.


Atomic number

A specific number that differs for each element, equal to the number of protons in the nucleus of each of its atoms.



The process of reduction of a compound's concentration over time. This can be through absorption, adsorption, degradation, dilution or transformation.



The action of one particle rubbing against the other in a filter media or ion exchange bed that can in time cause breakdown of the particles.


Available chlorine

A measure of the amount of chlorine available in chlorinated lime, hypochlorite compounds, and other materials.





The flow of water in a medium in a direction opposite to normal flow. Flow is often returned into the system by backflow, if the wastewater in a purification system is severely contaminated.


Back Pressure

Pressure that can cause water to backflow into the water supply when a user's waste water system is at a higher pressure than the public system.


Back siphonage

Reverse seepage of water in a distribution system.



Reversing the flow of water back through the filter media to remove entrapped solids.



Microscopically small single-cell organisms, that reproduce by fission of spores.


Bacterial water contamination

The introduction of unwanted bacteria into a water body.



An alkaline substance that has a pH that exceeds 7,5.


Bed Load

Sediment particles resting on or near the channel bottom that are pushed or rolled along by the flow of water.



Salts containing the anion HCO3-. When acid is added, this ion breaks into H2O and CO2, and acts as a buffer.



Chemicals that hold short fibers together in a cartridge filter.



The increase in concentration of a substance in living organisms, as they take in contaminated air, water, or food, due to slow metabolization and excretion.


Biochemical Oxygen Demand (BOD)

The amount of oxygen (measured in mg/L) that is required for the decomposition of organic matter by single-cell organisms, under test conditions. It is used to measure the amount of organic pollution in wastewater.



A chemical that is toxic to microrganisms. Biocides are often used to eliminate bacteria and other single-cell organisms from water.


Biodegradable pollutants

Pollutants that are capable of decomposing under natural conditions.



Population of various microrganisms, trapped in a layer of slime and excretion products, attached to a surface.


Biological contaminants

Living organisms such as viruses, bacteria, fungi, and mammal and bird antigens that can cause harmful health effects to humans.


Biologically activated carbon

Activated carbon that supports active microbial growth, in order to aid in the degradation of organics that have been absorbed on its surface and in its pores.


Biological oxidation

Decomposition of complex organic materials by microrganisms through oxidation.



The use of living organisms to test the suitability of effluents for discharge into receiving waters and to test the quality of such waters downstream from the discharge.



The biological treatment of wastewater and sludge, by inducing the breakdown of organics and hydrocarbons to carbon dioxide and water.



Water that contains waste of humans, animals or food.


Blind spots

Any place on a filter medium where fluids cannot flow through.



A build-up of particles in a filter medium, that prevents fluids from flowing through.


Boiling point

The temperature at which the vapor pressure of a liquid equals the pressure of its surface. The liquid will than vaporize If the pressure of the liquid varies, the actual boiling point varies. For water the boiling point is 212 degrees Fahrenheit (100 degrees Celsius).


Bottled water

Water that is sold in plastic containers for drinking water and/ or domestic use.


Brackish water

Water that is neither falls in the category of salt water, nor in the category of fresh water. It holds the middle between either one of the categories.


Breakpoint chlorination

Addition of chlorine to water until there is enough chlorine present for disinfection of water.



Crack or break in a filter bed that allows the passage of floc or particulate matter through a filter.



Highly salty and heavily mineralized water, containing heavy metal and organic contaminants.



A substance that reacts with hydrogen or hydroxyl ions in a solution, in order to prevent a change in pH.





Solid dewatered residue on a filter media after filtration.


Calcium hypo chlorite

A chemical that is widely used for water disinfection, for instance in swimming pools or water purification plants. It is especially useful because it is a stable dry powder and can be made into tablets.


Candle filter

A relatively coarse aperture filter, designed to retain a coat of filter medium on an extended surface.


Capillary action

Water that at some point rises higher than that portion of its surface, not in contact with the solid surface. This is due to adhesion, cohesion and surface tension where later touches a solid.


Capillary membranes

Membranes about the thickness of a human hair, used for Reverse Osmosis, nanofiltration, ultrafiltration and microfiltrtion.


Capillary zone

Soil area above the water table where water can rise up slightly through the cohesive force of capillary action.



Any dissolved pollutant that can induce cancer.


Cartridge filter

Disposable filter device that has a filter range of 0.1 micron to 100 microns.



Chemical compounds related to carbon dioxide.


Carbonate hardness

Hardness of water caused by carbonate and bicarbonate by-products of calcium and magnesium.



Chemical that increases the rate of a reaction but does not take a direct part in the reaction, so that it is still intact after the reaction has taken place.



A site in electrolysis where cations in solution are neutralized by electrons that plate out on the surface or produce a secondary reaction with water.



A negatively charged ion, resulting from dissociation of molecules in solution.



A separation process, which uses the action of centrifugal force to promote accelerated settling of particles in a solid-liquid mixture.



Colony Forming Units. This is a measure that indicates the number of microrganisms in water.


Check valve

A valve that allows water to stream in one direction and will then close to prevent development of a back-flow.


Chelating agents

Organic compounds that have the ability to draw ion from their water solutions into soluble complexes.


Chemical Oxygen Demand (COD)

The amount of oxygen (measured in mg/L) that is consumed in the oxidation of organic and oxidasable inorganic matter, under test conditions. It is used to measure the total amount of organic and inorganic pollution in wastewater. Contrary to BOD, with COD practically all compounds are fully oxidized.


Chemical pollution

Introduction of chemical contaminants into a water body.


Chemical weathering

Dissolving of rock by exposure to rainwater, surface water, oxygen, and other gases in the atmosphere, and compounds secreted by organisms.



A chemical complex that consists of chlorine and ammonia. It serves as a water disinfectant in public water supplies in place of chlorine because chlorine can combine with organics to form dangerous reaction products. In which forms chloramines exist depends on the physical/ chemical properties of the water source.


Chlorinated hydrocarbons

Hydrocarbons that contain chlorine. These include a class of persistent insecticides that accumulate in the aquatic food chain. Among them are DDT, aldrin, dieldrin, heptachlor, chlordane, lindane, endrin, Mirex, hexachloride, and toxaphene.


Chlorinated solvent

An organic solvent containing chlorine atoms that is often used as aerosol spray container, in highway paint, and dry cleaning fluids.



A water purification process in which chlorine is added to water for disinfection, for the control of present microrganisms. It is also used in the oxidation of compound impurities in water.


Chlorine-contact chamber

The part of a water treatment plant where effluent is disinfected by chlorine.



The clearness of a liquid.



Destabilisation of colloid particles by addition of a reactive chemical, called a coagulant. This happens through neutralization of the charges.



Liquid particles in suspension that unite to create particles of a greater volume.


Coastal zone

Lands and waters near the coast, whose uses and ecology are affected by the sea.


Coliform bacteria

Bacteria that serve as indicators of pollution and pathogens when found in water. These are usually found in the intestinal tract of humans and other warm-blooded animals.


Coliform index

A rating of the purity of water based on a count of coliform bacteria.


Collector sewers

Pipes to collect and carry wastewater from individual sources to an interceptor sewer that will carry it to a treatment facility.



Matter of very small particle size, in the range of 10-5 to 10-7 in diameter.


Combined sewer

A sewer system that carries both sewage and rain water runoff.


Composite sample

A series of water samples taken over a given period of time and weighted by flow rate.



Two or more different elements held together in fixed proportions by attractive forces called chemical bonds.



The totality of different substances that are left behind in a filter medium after filtration.



The amount of material dissolved in a unit of solution, expressed in mg/L.


Concentration process

The process of increasing the number of particles per unit volume of a solution, usually by evaporating the liquid.



Water obtained by condensation of water vapor.



The change of state from a gas to a liquid.



The amount of electricity the water can conduct. It is expressed in a chemical magnitude. Please use also our information about TDS and conductivity.



A natural or artificial channel through which fluids may be transported.


Consumptive water use

Water removed from available supplies without return to a water resources system; water used in manufacturing, agriculture, and food preparation.


Contact time

The length of time a substance is in contact with a liquid, before it is removed by filtration or the occurrence of a chemical change.



Any foreign component in a substance, for example in water.


Conventional sewer systems

Systems that were traditionally used to collect municipal wastewater in gravity sewers and convey it to a central primary or secondary treatment plant, before discharge on receiving surface waters.


Conveyance loss

Water loss in pipes and channels by leakage or evaporation.


Cooling tower

Large tower used to transfer the heat in cooling water from a power or industrial plant to the atmosphere either by direct evaporation or by convection and conduction.



Ability of water to dissolve or break down certain substances, particularly metals.


Cross flow filtration

A process that uses opposite flows across a membrane surface to minimize particle build-up.



A microorganism in water that causes gastrointestinal illness in humans. It is commonly found in untreated surface water and can be removed by filtration. It is resistant to disinfectants such as chlorine.


Cultural eutrophication

Decline of the oxygen rate in water, which has serious consequences for aquatic life, caused by humans.



The portion of a stream or body of water, which is moving much faster than the rest of the water. The progress of the water is principally concentrated in the current.



The length of time a filter can be used before it needs cleaning, usually including cleaning time.





Any process that serves to reduce the alkalinity of water.



The process of removing carbon dioxide from water, using contact towers or air scrubbers.



The breakdown of organic matter by bacteria and fungi, to change the chemical structure and physical appearance of matter.



The removal of fluoride from drinking water to prevent teeth damage.


Defoaming agents

Chemicals that are added to wastewater discharges to prevent the water from foaming when it is discharged into a receiving water body.



The process of removing dissolved gasses from water, using vacuum or heat.



Process that serves to remove all ionized substances from a solution. Most commonly is the exchange process where cations and anions are removed independently of each other.



Processes to remove minerals from water, usually the term is restricted to ion exchange processes.



Demineralised water. Water that is treated to be contaminant-, mineral- and salt free.



Removal of nitrate and nitrate product from water to produce a quality that answers common water standards.



The weight of a certain amount of water. It is usually expressed in kilograms per cubic meter.


Depth filtration

Treatment process in which the entire filter bed is used to trap insoluble and suspended particles in its voids as water flows through it.



The removal of salt from seawater or brackish water to produce drinking water, using various techniques.



The opposite of adsorption; the release of matter from the adsorption medium, usually to recover material.



A water-soluble cleansing agent, other than soap.



The separation of water from sludge, to produce a solid cake.



A component of the ozone contacting system in an ozone generator that allows diffusion of an ozone containing gas.



The movement of gas molecules or aerosols into liquids, caused by a concentration gradient.


Diluting water

Distilled water that has been stabilized, buffered, and aerated. It is often applied in the BOD tests.


Direct run-off

Water that flows from the ground surface directly into streams, rivers, and lakes.



Flow of surface water in a stream or canal.



Fluids or gasses to disinfect filters, pipelines, systems, etc.



The decontamination of fluids and surfaces. To disinfect a fluid or surface a variety of techniques are used, such as ozone disinfection. Often disinfection means eliminating the present microrganisms with a biocide.



The process during which solid particles mix molecule by molecule with a liquid and appear to become part of the liquid.


Dissolved oxygen

The amount of oxygen dissolved in water at a certain time, expressed in ppm mg/L.


Dissolved solids

Solids material that totally dissolves in water and can be removed by means of filtration.



Water treatment method where water is boiled to steam and condensed in a separate reservoir. Contaminants with higher boiling points than water do not vaporize and remain in the boiling flask.



Cleaning, deepening, or widening of a waterway, using a machine (dredge) that removes materials by means of a scoop or a suction device.



Term applied to periods of less than average precipitation over a certain period of time.





The outlet or outflow of any system that deals with water flows, for an oxidation pond for biological water purification. It is the product water of the given system.



A device used to inject a chemical solution into wastewater during water treatment.


Electrical charge

The charge on an ion, declared by its number of electrons. A Cl- ion is in fact a Cl atom which has acquired an electron, and a Ca++ ion is a Ca atom, which has lost two electrons.



Substance that dissociates into ions when it dissolves in water.



A process that uses electrical currents, applied to permeable membranes, to remove minerals from water.



Process where electrical energy will change in chemical energy. The process happens in an electrolyte, a watery solution or a salt melting which gives the ions a possibility to transfer between two electrodes. The electrolyte is the connection between the two electrodes, which are also connected to a direct current. If you apply an electrical current, the positive ions migrate to the cathode while the negative ions will migrate to the anode. At the electrodes, the cations will be reduced, and the anions will be oxidated.



Negatively charged building blocks of an atom that circle around the nucleus.



The distinctive building blocks of matter that make up every material substance.



A chemical that helps suspending one liquid in another.



Dispersion of one liquid in another liquid, occurs when a liquid in insoluble.


End-of-pipe techniques

Techniques for water purification that serve the reduction pollutants after they have formed.



When the addition of nutrients, such as nitrogen and phosphorus, from sewage effluent or agricultural runoff to surface water, greatly increases algal growth.



The wearing away of the land surface by wind, water, ice or other geological agents. Erosion occurs naturally from weather or runoff but is often intensified by human land use practices.


Eschericha coli (E. coli)

Coliform bacterium that is often associated with human and animal waste and is found in the intestinal court. It is used by health departments and private laboratories to measure the purity of water.



Region of interaction between rivers and near-shore ocean waters, where tidal action and river flow mix fresh and salt water. Therefore, estuaries mainly consist of brackish water.



Referring to water that is rich in nutrients such as nitrogen and phosphorous.



Enrichment of water, which causes excessive growth of aquatic plants and increasing activity of anaerobic microrganisms. As a result the oxygen levels in the water quickly decline and the water chokes, making life impossible for aerobic water organisms.



The process of the passage of water from liquid to vapor.


Evaporation ponds

Areas where sewage sludge is dumped and dried.



The loss of water from the soil through vaporizing, both by direct evaporation and by transpiration from plants.




Facultative bacteria

Bacteria that can live under aerobic or anaerobic conditions.



The conversion of organic matter to methane, carbon dioxide and other molecules by anaerobic bacteria.


Filter medium

The permeable material that separates solids from liquids passing through it.



A liquid that has passed through the filter medium.



Separation of a solid and a liquid by using a porous substance that only lets the liquid pass through.


First draw

The water that comes out when a tap is first opened. It is likely that is has the highest level of lead contamination from weathering of pipelines.



Reproduction of microrganisms by means of cell division.



A flocculent mass that is formed in the accumulation of suspended particles. It can occur naturally but is usually induced in order to be able to remove certain particles from wastewater.



The accumulation of destabilized particles and micro flakes, and subsequently the formation of sizeable flakes. One must add another chemical called flocculent in order to facilitate the formation of flakes called flocs.



A solids-liquid or liquid-liquid separation procedure, which is applied to particles of which the density is lower than that of the liquid they are in. there are three types: natural, aided and induces flotation.



The discharge rate of a resource, expressed in volume during a certain period of time.


Flow augmentation

The addition of water to meet flow needs.



The rate at which a Reverse Osmosis Membrane allows water to pass through it.



The deposition of organic matter on the membrane surface, which causes inefficiencies.



The subdivision of a solid in fragments. The fragments will then adhere to the nearest surface.



The change of a liquid into a solid as temperature decreases. For water, the freezing point is 0 degrees Celsius.



Water containing less than 1 mg/l of dissolved solids of any type.





A unit that is now almost entirely out of date. It is equivalent to 3.785 liters.



A microrganism that is commonly found in untreated surface water and can be removed by filtration. It is resistant to disinfectants such as chlorine.


Granular activated carbon

The heating of carbon to encourage active sites to absorb pollutants.


Gray Water

Domestic wastewater composed of wash water from kitchen, bathroom, and laundry sinks and from tubs, and washers.



Water that can be found in the saturated zone of the soil; a zone that consists merely of water. It slowly moves from places with high elevation and pressure to places with low elevation and pressure, such as rivers and lakes.


Groundwater discharge

Ground water entering coastal waters, which has been contaminated by land-fill leachates, deep well injection of hazardous wastes and septic tanks.


Groundwater hydrology

The branch of hydrology that deals with the occurrence, movements, replenishment and depletion, properties and methods of investigation and utilization of groundwater.



A deeply eroded channel created by the concentrated flow of water.





The time required for a pollutant to lose one-half of its original concentration.


Hard water

Water that contains a great number of positive ions. The hardness is determined by the number of calcium and magnesium atoms present. Soap usually dissolves badly in hard water.


Heat exchanger

A component that is utilized to remove heat from or ad heat to a liquid.


Heavy metals

Metals that have a density of 5.0 or higher and a high elemental weight. Most are toxic to humans, even in low concentrations.


Heavy water

Water in which all the hydrogen atoms have been replaced by deuterium.


Henry's Law

A way of calculating the solubility of a gas in a liquid, based on temperature and partial pressure, by means of constants.


Homeowner water system

A water system that supplies piped water to a single residence.



The addition of water vapor to air.


Hydraulic conductivity

The rate at which water can move through a permeable medium.


Hydraulic gradient

In general, the direction of groundwater flow due to changes in the depth of the water table.



Organic compounds that are built of carbon and hydrogen atoms and are often used in petroleum industries.


Hydroelectric power water use

The use of water in the generation of electricity at plants where the turbine generators are driven by falling water.


Hydrogen sulfide (H2S)

A gas emitted during organic decomposition by a select group of bacteria, which strongly smells like rotten eggs.



The science of chemistry and movement of groundwater.



A chart that measures the amount of water flowing past a point as a function of time.



The decomposition of organic compounds by interaction with water.


Hydrologic cycle

The natural cycle of water passing through the environment, including evaporation, condensation, retention and run-off.



Having an affinity for water.



Having an aversion for water.



Region that includes all the earth's liquid water, frozen water, floating ice, frozen upper layer of soil, and the small amounts of water vapor in the atmosphere.


Hypo chlorite

An anion that forms products such as calcium and sodium hypo chlorite. These products are often used for disinfection and bleaching.


Hypoxic waters

Waters with dissolved oxygen concentrations of less than 2 mg/L, the level generally accepted as the minimum required for life and reproduction of aquatic organisms.





The solid form of water.


Imhoff cone

A clear, cone-shaped container used to measure the volume of settle able solids in a specific volume of water.



The inability of two or more solids or liquids to readily dissolve into one another.



Not easily penetrated by water.



Particles or other objects that cause water to be unclear.



Any biological entity or process, or community whose characteristics show the presence of specific environmental conditions or pollutants.


Indicator organisms

Microrganisms, such as coliforms, whose presence is indicative for pollution or for the presence more harmful microrganisms.


Indicator tests

Tests for a specific contaminant, group of contaminants, or constituent which signals the presence of something else.


Indirect discharge

Introduction of pollutants from a non-domestic source into a publicly owned wastewater treatment system. Indirect dischargers can be commercial or industrial facilities whose wastes enter local sewers.



Penetration of water into a medium, for instance the soil.



The stream of water that enters any system or treatment unit.



chemical that interferes with a chemical reaction, such as precipitation.



The introduction of a chemical or medium into the process water to alter its chemistry or filter specific compounds.



An atom in a solution that is charged, either positively (cations) or negatively (anions).


Ion exchange

The replacement of undesirable ions with a certain charge by desirable ions of the same charge in a solution, by an ion-permeable absorbent.


Inorganic chemicals

Chemical substances of mineral origin, not of basically carbon structure.



Applying water or wastewater to land areas to supply the water and nutrient needs of plants.




Jar test

A laboratory test procedure with differing chemical doses, mix speeds, and settling times, to estimate the minimum or ideal coagulant dose required to achieve water quality goals.




Kinetic Energy

Energy possessed by moving water.


Kinetic rate coefficient

A number that describes the rate at which a water constituent such as a biochemical oxygen demand or dissolved oxygen rises or falls.




Laboratory water

Purified water used in the laboratory as a basis to create solutions or making dilutions. It contains no interfering substances.



A shallow pond where sunlight, bacterial action, and oxygen work to purify wastewater.



An inland body of water, usually fresh water, formed by glaciers, river drainage, etc. It is usually larger than a pool or pond.


Laminar flow

A flow in which rapid fluctuations are absent.


Land Application

Discharge of wastewater onto the ground for treatment or reuse.


Langelier Index (LI)

An index reflecting the equilibrium pH of a water with respect to calcium and alkalinity; used in stabilizing water to control both corrosion and scale deposition.


Large water system

A water system that services more than 50,000 customers.



Water that contains solute substances, so that it contains certain substances in solution after percolation through a filter or soil.



The process by which soluble constituents are dissolved and filtered through the soil by a percolating fluid.



A species of ions in the feed of an ion exchanger present in the effluent.


Light absorption

The amount of light a certain amount of water can absorb over time.



Common water treatment chemical. Lime can be deposed on walls of showers and bathrooms, after lime has reacted with calcium to form limestone.



The study of the physical, chemical, hydrological, and biological aspects of fresh water.



A state of matter, neither gas nor solid, that flows and takes the shape of its container.




Maximum Contaminant Level (MCL)

The maximum level of a contaminant allowed in water by federal law. Based on health effects and currently available treatment methods.


Mechanical aeration

Use of mechanical energy to inject air into water to cause a waste stream to absorb oxygen.


Mechanical flotation

A term used in the mineral industry to describe the use of dispersed air to produce bubbles that measure 0.2 to 2 mm in diameter.



Materials that form a barrier to the passage of certain suspended solids or dissolved liquids in filters.


Medium-size water system

A water system that serves 3,300 to 50,000 customers.



The change of a solid into a liquid.



A thin barrier that allows some compounds or liquids to pass through, and troubles others. It is a semi-permeable skin of which the pass-through is determined by size or special nature of the particles. Membranes are commonly used to separate substances.



Reservoirs and lakes which contain moderate quantities of nutrients and are moderately productive in terms of aquatic animal and plant life.



Conversion of food, for instance soluble organic matter, to cellular matter and gaseous by-products through a biological process.



Micro Filtration System, it serves full automatic solid/ liquid separation.


Microbial growth

The multiplication of microrganisms such as bacteria, algae, diatoms, plankton, and fungi.



A unit to describe a measure of length, equal to one millionth of a meter.



Organisms that are so small that they can only be observed through a microscope, for instance bacteria, fungi or yeasts.


Mineral Water

Contains large amounts of dissolved minerals such as calcium, sodium, magnesium, and iron. Some tap waters contain as many or more minerals than some commercial mineral waters. There is no scientific evidence that either high or low mineral content water is beneficial to humans.



The ability of two liquids to mix.



Liquid particles measuring 40 to 500 micrometers, are formed by condensation of vapor. By comparison, fog particles are smaller than 40 micrometers.



Various elements, compounds or both, that are mixed.



Combinations of two or more atoms of the same or different elements held together by chemical bonds.


Municipal discharge

Discharge of effluent from wastewater treatment plants, which receive wastewater from households, commercial establishments, and industries in the coastal drainage basin.


Municipal sewage

Liquid wastes, originating from a community. They may have been composed of domestic wastewaters or industrial discharges.


Municipal Sludge

Semi liquid residue that remains from the treatment of municipal water and wastewater.





The addition of substances to neutralize water, so that it is neither acid, nor basic. Neutralization does not specifically mean a pH of 7.0, it just means the equivalent point of an acid-base reaction.



Uncharged building blocks of an atom that play a part in radio-activity. They can be found in the nucleus.



A biological process, during which nitrifying bacteria convert toxic ammonia to less harmful nitrate. It is commonly used to remove nitrogen substances from wastewater, but in lakes and ponds it occurs naturally.


Non-point sources

Diffuse water pollution sources without a specific point of origin. The pollutants are generally carried off the land by storm water. Common non-point sources are agriculture and atmospheric disposal.



Water that is unsafe or unpalatable to drink because it contains pollutants, contaminants, minerals or infective agents.



The center of an atom, that contains protons and neutrons and carries a positive charge.


Nuisance Contaminant

Constituents in water, which are not normally harmful to health but may cause offensive taste, odor, color, corrosion, foaming, or staining.



Any substance that promotes growth with living organisms. The term is generally applied to nitrogen and phosphorus in wastewater but is also applied to other essential and trace elements.


Nutrient Pollution

Contamination of water resources by excessive inputs of nutrients. In surface waters, excess algal production is a major concern.




Oligotrophic lakes

Deep clear lakes with few nutrients, little organic matter and a high dissolved-oxygen level.


Organic matter

Substances of (dead) plant or animal matter, with a carbon-hydrogen structure.



Water molecules passing through membranes naturally, to the side with the highest concentration of dissolved impurities.



The place where a wastewater treatment plant discharges treated water into the environment.


Overflow rate

One of the guidelines for design of the settling tanks and clarifiers in a treatment plant to determine if tanks and clarifiers are used enough.



A chemical reaction in which ions are transferring electrons, to increase positive valence.


Oxidation pond

A man-made body of water in which waste is consumed by bacteria.


Oxidation-reduction potential

The electric potential required to transfer electrons from the oxidant to the reductant, used as a qualitative measure of the state of oxidation in water treatment systems.


Oxygen depletion

The reduction of the dissolved oxygen level in a water body.



An unstable oxidizing agent, that consists of three oxygen atoms and can be found in the ozone layer in the atmosphere. It is produced by electrical discharge through oxygen or by specifically designed UV-lamps.


Ozone generator

A device that generates ozone by passing a voltage through a chamber that contains oxygen. It is often used as a disinfection system.





A variable, measurable property whose value is a determinant of the characteristics of a system such as water. Temperature, pressure, and density are examples of parameters.


Partial pressure

That pressure of a gas in a liquid, which is in equilibrium with the solution. In a mixture of gases, the partial pressure of any one gas is the total pressure times the fraction of the gas in the mixture (by volume or number of molecules).


Particle size

The sizes of a particle, determined by the smallest dimension, for instance a diameter. It is usually expressed in micron measurements.


Particulate loading

The mass of particulates per unit volume of water.


Parts per billion

Expressed as ppb; a unit of concentration equivalent to the µg/l.


Parts per million

Expressed as ppm; a measure of concentration. One ppm is one-unit weight of solute per million unit weights of solution. In water analysis the ppm is equivalent to mg/l.



The elimination of microrganisms by heat applies for a certain period of time.



Disease-producing microrganisms.


Percent saturation

The amount of a substance that is dissolved in a solution compared to the amount that could be dissolved in it.


Percolating water

Water that passes through rocks or soil under the force of gravity.


Periodic chart

Arrangement of elements in order of increasing atomic numbers, created by a scientist called Mendelejef.



The ability of a medium to pass a fluid under pressure.



Refers to the length of time a compound stays in the environment, once introduced.



The value that determines if a substance is acid, neutral or basic, calculated from the number of hydrogen ions present. It is measured on a scale from 0 to 14, on which 7 means the substance is neutral. pH values below 7 indicate that a substance is acidic and pH values above 7 indicate that it is basic.



A state of matter. This can be solid, liquid or gaseous.



The process of conversion of water and carbon dioxide to carbohydrates. It takes place in the presence of chlorophyll and is activated by sunlight. During the process oxygen is released. Only plants and a limited number of microrganisms can perform photosynthesis.


Physical and chemical treatment

Processes generally used in wastewater treatment facilities. Physical processes are for instance filtration. Chemical treatment can be coagulation, chlorination, or ozone treatment.


Physical weathering

Breaking down of rock into bits and pieces by exposure to temperature and changes and the physical action of moving ice and water, growing roots, and human activities such as farming and construction.



Free-floating, mostly microscopic aquatic plants.


Pilot tests

The testing of a cleanup technology under actual site conditions in a laboratory in order to identify potential problems before implementation.



Point-Of-Entry treatment. Total water treatment at the inlet to an entire building or facility.



An opening in a membrane or medium that allows water to pass through.


Point source

A stationary location from which pollutants are discharged. It is a single identifiable source of pollution, such as a pipeline or a factory.


Polar substance

A substance that carries a positive or negative charge, for instance water.



A contaminant at a concentration high enough to endanger the life of organisms.



Persistent Organic Pollutants, complex compounds that are very persistent and difficultly biologically degradable.


Potable water

Water that is safe for drinking and cooking.



The ability of one chemical to increase the effect of another chemical.


Potentiometric surface

The surface to which water in an aquifer can rise by hydrostatic pressure.



Point-Of-Use treatment. Water treatment at a limited number of outlets in a building, for less than the whole building.



An insoluble reaction product in an aqueous chemical reaction.


Precipitation process

The altering of dissolved compounds to insoluble or badly soluble compounds, in order to be able to remove the compounds by means of filtration.


Pressure sewers

A system of pipes in which water, wastewater, or other liquid is pumped to a higher elevation.



Processes used to reduce or eliminate wastewater pollutants from before they are discharged.


Primary wastewater treatment

The removal of suspended, floating and precipitated solids from untreated wastewater.


Process water

Water that serves in any level of the manufacturing process of certain products.


Product water

Water that has passed through a water treatment plant and is ready to be delivered to consumers.



Positively charged building blocks of an atom that are centered in the nucleus.



Large microrganisms, which consume bacteria.


Public water system

A system that provides piped water for human consumption to at least 15 service connections or regularly serves 25 individuals.



Biological decomposition of organic matter; associated with anaerobic conditions.



Substance that is produces by bacteria and it fairly stable. It causes fever in mammals.




Qualitative water assessment

Analyses of water used to describe the visible or aesthetic characteristics of water.


Quantitative water assessment

Use of analyses of water properties and concentrations of compounds and contaminants in order to define water quality.


Quicksilver water

A solution of mercury nitrate used in gilding.





Having the property of releasing radiation.


Raw sewage

Untreated wastewater and its contents.


Raw water

Intake water before any treatment or use.



Renewing air supplies in the lower layers of a reservoir in order to raise oxygen levels.



Process in which carbon dioxide is bubbled into treatment water in order to lower the pH.


Receiving waters

A river, lake, ocean, stream or other watercourse into which wastewater or treated effluent is discharged.


Recharge Area

An area where rainwater soaks through the ground to reach an aquifer.



Recycling water after it is used. Often it has to pass a wastewater purification system before it can be reused.



Shortened term for reduction/ oxidation reactions. Redox reactions are a series of reactions of substances in which electron transfer takes place. The substance that gains electrons is called oxidizing agent.



A chemical reaction in which ions gain electrons to reduce their positive valence.



Putting the desired counter-ion back on the ion exchanger, by displacing an ion of higher affinity with one of lower affinity.


Reserve Capacity

Extra treatment capacity built into wastewater treatment plants and sewers to be able to catch up with future flow increases due to population growth.



A natural or artificial holding area used to store water.



The dry solids remaining after the evaporation of a sample of water or sludge.



The breaking of an emulsion into its individual components.


Reverse Osmosis process

The Reversed Osmosis (RO) process uses a semi-permeable membrane to separate and remove dissolved solids, organics, pyrogens, submicron colloidal matter, viruses, and bacteria from water. The process is called 'reverse' osmosis since it requires pressure to force pure water across a membrane, leaving the impurities behind.



The part of precipitation water that runs off the land into streams or another surface water.



Safe water

Water that does not contain harmful bacteria, toxic materials, or chemicals, and is considered safe for drinking.


Safe yield

The annual amount of water that can be taken from a source of supply over a period of years without depleting that source beyond its ability to be naturally refilled.



The presence of soluble minerals in water.


Sand filtration

Sand filtration is a frequently used and very robust method to remove suspended solids from water. The filtration medium consists of a multiple layer of sand with a variety in size and specific gravity. Sand filters can be supplied in different sizes and materials both hand operated and fully automatically.


Saturated zone

The area below the water table where all open spaces are filled with water.



The condition of a liquid when it has taken into solution the maximum possible quantity of a given substance.



The precipitate that forms on surfaces in contact with water as the result of a physical or chemical change.



Use of screens to remove coarse floating and suspended solids from sewage.


Secondary treatment

The removal or reduction of contaminants and BOD of effluent from primary wastewater treatment.



Settling of solid particles in a liquid system due to gravity.



Soil, sand, and minerals washed from land into water, usually after rain.


Semi-confined aquifer

An aquifer partially confined by soil layers of low permeability through which recharge and discharge can still occur.



A medium that allows water to pass through, but rejects dissolved solids, so that it can be used to separate solids from water.


Separate sewer

A sewer system that carries only sanitary sewage; no storm-water runoff. When a sewer is constructed this way, wastewater treatment plants can be sized to treat sanitary wastes only and all of the water entering the plant receives complete treatment at all times.



The isolation of the various compounds in a mixture.


Septic tank

An underground storage tank for wastes from homes not connected to a sewer line. Waste goes directly from the home to the tank.


Settleable solids

Those suspended solids in wastewater that will settle over a certain period of time and are removed in that way.



The process of sinking of a substance sinking in water. This occurs when the substance does not dissolve in water and its density is larger than that of water.



Waste fluid in a sewer system.


Sewage contamination

The introduction of untreated sewage into a water body.


Sewage sludge

Sludge produced in a public sewer.



The entire system of sewage collection, treatment, and disposal.



A semi-solid residue, containing microoroganisms and their products, from any water treatment process.



The removal of calcium and magnesium from water to reduce hardness.


Soft water

Any water that does not contain large concentrations of the dissolved minerals calcium or magnesium.



Removal of wastewater from a waste or changing it chemically to make it less permeable and susceptible to transport by water.



The amount of mass of a compound that will dissolve in a unit volume of water.



Matter dissolved in a liquid, such as water.



Substance (usually liquid) capable of dissolving one or more other substances.



A device that introduces compressed air into a liquid.



Injection of air below the water table to strip dissolved volatile organic compounds and to facilitate aerobic biodegradation of organic compounds.


Specific conductance

Method to estimate the dissolved solid content of a water supply by testing its conductivity.



Ground water seeping out of the earth where the water table exceeds the ground surface.


Stoke's Law

A method to calculate the rate of fall of particles through a fluid, based on density, viscosity and particle size.



The transitions of water directly from the solid state to the gaseous state, without passing through the liquid state.


Surface tension

The elastic-like force in a body, especially a liquid, tending to minimize, or constrict, the area of the surface.


Surface water

All water naturally open to the atmosphere, concerning rivers, lakes, reservoirs, ponds, streams, impoundments, seas, estuaries and wetlands.


Suspended solids

Solid organic or inorganic particles that are held in suspension in a solution.



The combined action of several chemicals, which produces a total effect greater than the effects of the chemicals separately.




Tertiary treatment

Advanced cleaning of wastewater that goes beyond the secondary or biological stage, removing nutrients such as phosphorus, nitrogen, and most BOD and suspended solids.


Thermal pollution

Discharge of heated water from industrial processes in receiving surface water, causing death or injury of aquatic organisms.



An analytical technique to determine how much of a substance is present in a water sample by adding another substance and measuring how much of that substance must be added to produce a reaction.



Total Dissolved Solids. The weight per unit volume of water of suspended solids in a filter media after filtration or evaporation. Please use also our information about TDS and conductivity.



Total Hardness. The sum of calcium and magnesium hardness, expressed as a calcium carbonate equivalent.



Total Solids. The weight of all present solids per unit volume of water. It is usually determined by evaporation. The total weight concerns both dissolved and suspended organic and inorganic matter.


Total Suspended Solids

All the solids in wastewater or sewage water, including suspended solids and filterable solids.


Toxic water pollutants

Compounds that are not naturally found in water at the given concentrations and that cause death, disease, or birth defects in organisms that ingest or absorb them.


Transmission lines

Pipelines that transport raw water from its source to a water treatment plant.



The ability of an aquifer to transmit water.



The process by which water vapor is released into the atmosphere after transpiring of living plants.


Treatment plant

A structure built to treat wastewater before discharging it into the environment.


Trickling filter

A wastewater treatment unit that contains medium material with bacteria. The stream of wastewater is trickled over the medium and the bacteria break down the organic wastes. Bacteria are collected on the filter medium.



Trihalomethanes. Toxic chemical substances that consist of a methane molecule and one of the halogen elements fluorine, bromine, chlorine and iodine attached to three positions of the molecule. They usually have carcinogenic properties.


Tube settler

Device using bundles of tubes to let solids in water settle to the bottom for removal by sludge.



A measure of non-transparency of water due to the presence of suspended matter.


Turbulent flow

A flow that contains may rapid fluctuations.




Ultra-violet oxidation

A process using extremely short wave-length light that can kill micro-organisms (disinfection) or cleave organic molecules (photo oxidation) rendering them polarized or ionized and thus more easily removed from the water.



The release of the contaminant that was captured by a filter medium.


Unsaturated Zone

The area above the water table where soil pores are not fully saturated with water.



An upward flow of water.



Ultra pure water creation demands a specialized way of working. A number of techniques are used amongst others; membrane filtration, ion exchanges, sub-micron filters, ultra-violette and ozone systems. The produced water is extremely pure and contains none to very low concentrations of salts, organic/ pyrogene components, oxygen, suspended solids and bacteria.


Urban run-off

Water from city streets domestic properties that carries pollutants into the sewer systems and receiving waters.



Ultra Violet. Radiation that has a wavelength shorter than visible light. It is often used to kill bacteria and destroy ozone.





The gaseous phase of substances such as water.



Conversion of a liquid into vapor.



A channel that serves the measurement of water flows.



The smallest life forms known, that are not cellular in nature. They live inside the cells of animals, plants and bacteria and often cause disease. They are made up of a chromosome surrounded by a protein shell.



The syrupiness of water and it determines the mobility of the water. When the temperature rises, the viscosity degrades; this means that water will be more mobile at higher temperatures.



Volatile Organic Compound. Synthetic organic compounds which easily vaporize and are often carcinogenic.





The spent or used water from a home, community, farm, or industry that contains dissolved or suspended matter.


Wastewater infrastructure

The plan or network for the collection, treatment, and disposal of sewage in a community.


Water monitoring

The process of constant control of a body of water by means of sampling and analyses.


Water pollution

The presence in water of enough harmful or objectionable material to damage water quality.


Water quality

The condition of water with respect to the amount of impurities in it.


Water recycling

Using water again for the same or another process step, after a small form of purification is applied.



A land area from which water drains to a particular water body.


Water solubility

The maximum possible concentration of a chemical compound dissolved in water.


Water storage pond

An impound for liquid wastes designed to accomplish some degree of biochemical treatment.


Water supply system

The collection, treatment, storage, and distribution of water from source to consumer.


Water system

A river and all its branches.


Water table

The surface of groundwater in the soil.



A spill over device used to measure or control water flows.



A deep hole with the purpose to reach underground water supplies.



An area that is saturated by surface water or groundwater, with vegetation adapted for life under those soil conditions.



The relative degree to which a fluid will spread into solid surface in the presence of other immiscible fluids.





Any biological substance, displaced from its normal habitat; a chemical foreign to a biological system.





The rate of production of cake from a dewatering device.



Zero discharge water

The principle of “zero discharge” is recycling of all industrial wastewater. This means that wastewater will be treated and used again in the process. Because of the water reuse wastewater will not be released on the sewer system or surface water.


Zeta potential

An electrokinetic measurement which can be used for the control of coagulation processes.


Zone of saturation

The space in the soil below the water table in which all the pores are filled with water. The water in the zone of saturation is groundwater.



Tiny aquatic animals eaten by fish.


Zwitter ions

Act as cations or as anions according to the environment in which they find themselves. In water technology they are usually organic macromolecules.