A – E | F – J | K – O | P – T | U – Z

Absolute Filter Rating
Filter rating meaning that 99.9 % of the particles larger than a specified micron rating will be trapped on or within the filter.

Absorption
The process in which one substance penetrates into the body of another substance.

Acid
A substance that releases hydrogen ions when dissolved in water. Most acids will dissolve the common metals, and will react with a base to form a neutral salt and water.

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

Activated Carbon
A granular material usually produced by the roasting of cellulose base substances, such as wood or coconut shells, in the absence of air. It has a very porous structure and is used in water conditioning as an adsorbent for organic matter and certain dissolved gases.

Adsorption
The process in which matter adheres to the surface of an adsorbent.

Algae
Plant life (green scum) containing chlorophyll is usually found in stagnant surface water.

Alkalinity
The quantitative capacity of a water or water solution to neutralize an acid. It is usually measured by titration with a standard acid solution of sulfuric acid, and expressed in terms of its calcium carbonate equivalent.

Anion
A negatively charged ion in solution, such as bicarbonate, chloride or sulfate.

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

Aquifer
A layer or zone below the surface of the earth that is capable of yielding a significant volume of water.

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

Backwash
The process in which beds of filter or ion exchange media are subjected to flow opposite to the service flow direction to loosen the bed and to flush suspended matter, collected during the service run, to waste.

Bacteria
Unicellular microorganisms that typically reproduce by cell division. Although usually classed as plants, bacteria contain no chlorophyll.

Base
A substance that releases hydroxyl ions when dissolved in water. Bases react with acids to form a neutral salt and water.

Bed
The exchange or filter media in a column or other tank or operational vessel.

Bed Depth
The height of the ion exchange or filter media in the vessel after preparation for service.

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

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

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

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

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

Calcium
One of the principal elements making up the earth’s crust, the compounds of which when dissolved make the water hard. The presence of calcium in water is a factor contributing to the formation of scale and insoluble soap curd that are a means of clearly identifying hard water.

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

Capacity
An expression of the quantity of an undesirable material that can be removed by a water conditioner between cleaning regeneration or replacement, as determined under standard test conditions. For ion exchange water softeners, the capacity is expressed in grains of hardness removal between successive regenerations and is related to the pound of salt used in regeneration. For filters, the capacity may be expressed in the length of time or total gallons delivered between servicing.

Carbon Dioxide
A gas present in the atmosphere and formed by the decay of organic matter; the gas in carbonated beverages; in water it forms carbonic acid.

Cation
An ion with a positive electrical charge, such as calcium, magnesium and sodium.

Cation Exchange
Ion exchange process in which cations in solution are exchanged for other cations from an ion exchanger.

Caustic
Any substance capable of burning or destroying animal flesh or tissue.

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

Cellulose Acetate
A synthetic polymer derived from naturally occurring cellulose and widely used in the fabrication of membranes. The polymers used for water purification membranes may be diacetate, triacetate or blends of these materials.

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

Chloramines
Chemicals used to disinfect municipal water. They are formed by reacting ammonia and free chlorine and may occur naturally when free chlorine combines with ammonia arising from the breakdown of vegetation. Chloramines are strong oxidants.

Chlorine
A gas, Cl₂, widely used in the disinfection of water and an oxidizing agent for organic matter, iron, etc.

Coagulant
A material, such as alum, which will form a gelatinous precipitate in water, and cause the agglomeration of finely divided particles into larger particles that, can then be removed by settling and/or filtration.

Compaction
The undesirable physical compression of a reverse osmosis or ultra filtration membrane that results in reduced flux rates. The phenomenon is accelerated at higher temperatures and pressures.

concentrate
A term used in distillation, electrodialysis, reverse osmosis, and ultrafiltration to describe that portion of the incoming feed water that has passed across the membrane but has not been converted to product water and is being sent to the drain.

Condensate
Water that has liquefied from steam.

Conductive
A measure of the ability of a solution to carry electricity; the reciprocal of the electrical resistance.

Conductivity
The quality or power to carry electrical current; in water, the conductivity is related to the concentration of ions capable of carrying electrical current. Conductivity is a quantitative measure that describes this ability. Solutions of inorganic ions are relatively good conductors (and exhibit high conductivity), whereas solutions of organic molecules are rather poor conductors (and exhibit low conductivity). Highly purified water is also a poor conductor. Conductivity is expressed in units of Siemens/cm (also known as mhos/cm).

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

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

Corrosion
The destructive disintegration of a metal by electrochemical means.

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

CTA
Cellulose triacetate. Used to manufacture reverse osmosis membranes.

Cycle
A series of events or steps that ultimately lead back to the starting point, such as the exhaustion. Example: regeneration cycle of an ion exchange system; sometimes incorrectly used in reference to a single step of a complete cycle.

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

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

Delta (∆) p
The pressure drop or loss in PSI between the inlet and the outlet of a water conditioner as the water flows.

Demineralization
The removal of ionized inorganic minerals and salts (not organic materials) from a solution by a two-phase ion exchange procedure; similar to deionization, and the two terms are often used interchangeably.

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

D.I. or DI
Abbreviation for “deionization”.

Disinfection
A process in which pathogens (disease producing bacteria) are killed; may involve disinfecting agents such as chlorine, or physical processes such as heating.

Dissolved Solids
The weight of matter in true solution in a stated volume of water; includes both inorganic and organic matter; usually determined by weighing the residue after evaporation of the water at 105 or 180 C.

Distillation
The process in which a liquid, such as water, is converted into its vapor state by heating and the vapor cooled and condensed to the liquid state and collected; used to remove solids and other impurities from water, multiple distillations are required for extreme purity.

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

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

Empty Bed Contact Time (EBCT)
The empty bed contact time is used to measure of how much contact occurs between particles, such as activated carbon, and water as the water flows through a bed of the particles. As the EBCT increases, the time available for the particles to adsorb solutes from the water also increases, as does the amount of solute removed from the water during its transit through the bed.

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

Equivalent Per Million
A unit of concentration used in chemical calculations, calculated by dividing the concentration in ppm or mg/1 by the equivalent weight.

Exhaustion
The state of an ion exchange material in which it is no longer capable of effective function due to the depletion of the initial supply of exchangeable ions; the exhaustion point may be defined in terms of a limiting concentration of matter in the effluent, or in the case of demineralization, in terms of electrical conductivity.