"Standing Guard for Your Water"

Guide to Water Purification Terminology

Unsure of what all those terms mean? Use this page to learn "water purification and filtration speak."


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 of organic matter and certain dissolved gases. Sometimes called "activated charcoal."
The process in which air is brought into intimate contact with water, often by spraying water through air or by bubbling air through water. Aeration may be used for oxidation of matter such as iron, or to cause the release of dissolved gases such as carbon dioxide from the water.
Anion Exchange
An ion exchange process in which anions in solution are exchanged for other anions. Demineralization is an example.
The process in which beds of tiler or ion exchange media are subjected to a flow in the opposite direction to loosen the bed and to flush suspended matter collected on the media.
Unicellular microorganisms which typically reproduce by cell division. Although usually classified as plants, bacteria contain no chlorophyll.
A feature of a carbon filter that is supposed to inhibit the growth of bacteria within the filter - usually by the addition of silver.
The ion exchange or filter media in a column in a tank or operational vessel.
Brackish Water
Water containing more than 1000 mg/L of dissolved solids is generally considered to be brackish.
Brine (RO)
Same as reject water. One of two streams of fluids generated by a reverse osmosis unit. It contains the impurities removed from the feed water.
Brine (Softening)
A strong solution of salt(s), such as sodium chloride, and water used in the regeneration of ion exchange water softeners but also applied to the mixed sodium, calcium and magnesium chloride waste solution from regeneration.
An expression of the quantity of an undesirable material which can be removed by a water conditioner between servicing of the media (ie. 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 pounds of salt used in regeneration. For filters, the capacity may be expressed in the length of time or total gallons delivered between servicing.
Cation Exchange
Ion exchange process in which cations in solution are exchanged for other cations from an ion exchanger.
A material, such as alum, which will form a gelatinous precipitate in water and cause the agglomeration of finely divided particles into larger particles which can then be removed by settling and/or filtration.
Very finely divided solid particles which will not settle out of a solution; intermediate between a true dissolved particle and a suspended solid which will settle out of solution. The removal of colloidal particles usually requires coagulation to form larger particles which may be removed by sedimentation and/or filtration.
Contact Time
The length of time water is in direct contact with activated carbon (RO) or chlorine. This is a major factor in determining how effectively impurities will be removed.
The destructive disintegration of a metal by electrochemical means.
Cycle Time
The amount of time in seconds elapsed between pump start and pump shut-down.
The removal of excess chlorine residual, often after super-chlorination.
Deionization (DI)
The removal of all ionized minerals and salts (both organic and inorganic) from a solution by a two-phase ion exchange procedure. First, positively charged ions are exchanged from a chemically equivalent amount of hydrogen ions. Second, negatively charged ions are removed by an anion exchange resin for a chemically equivalent amount of hydrogen ions. The hydrogen and hydroxide ions introduced in this process unite to form water molecules. The term is often used interchangeably with demineralization.
A process in which pathogenic, disease producing bacteria are killed. May involve disinfecting agents such as chlorine or physical process such as heating.
Dissolved Solids
The weight of matter in true solution in a stated volume of water. Includes both inorganic and organic matter and is usually determined by weighing the residue after evaporation of the water at 105°F or 180°C.
The process in which a liquid, such as water, is converted into its vapour state by heating and the vapour 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.
Feed Pressure
The pressure at which water is supplied to the RO module.
Feed Water
Refers to the water supply that is put into a water treatment system for processing.
The agglomeration of finely divided suspended solids into larger, usually gelatinous, particles. The development of a "floc" after treatment with a coagulant by gentle stirring or mixing.
Flow Control
A device designed to limit the flow of water or regenerant to a predetermined value over a broad range of inlet water pressures.
Flow Rate
The quantity of water or regenerant which passes a given point in a specific unit of time, often expressed in gallons per minute.
The flow rate of water through reverse osmosis membranes, per square foot of surface.
The process in which undesirable foreign matter accumulates in a bed of filter media or ion exchanger, clogging pores and coating surfaces and thus inhibiting or retarding the proper operation of the bed.
Grains per Gallon (gpg)
A common basis for reporting water analyses in the US and Canada. One grain per US gallon equals 17.12 milligrams per liter (mg/L) or parts per million (ppm).
A natural mineral, primarily composed of complex silicates, which can be coated with manganese oxide to form a catalytic absorptive surface. This surface is used to attract ferrous iron and manganese as well as to adsorb dissolved oxygen which is used to oxidize iron, manganese or hydrogen sulfide.
A characteristic of natural water due to the presence of dissolved calcium and magnesium. Water hardness is responsible for most scale formation in pipes and water heaters and forms insoluble "curd" when it reacts with soap. Hardness is usually expressed in grains per gallon (gpg).
The chemical degradation of an RO membrane in water due to certain conditions such as high pH. Cellulose based membranes are quite susceptible to hydrolysis while the TFC type are virtually immune.
An atom, or group of atoms, which function as a unit and have a positive or negative electrical charge due to the gain or lose of one or more electrons.
Ion Exchange
A reversible process in which ions are released from an insoluble permanent material in exchange for other ions in a surrounding solution; the direction of the exchange depends upon the affinities of the ion exchanger for the ions present and the concentrations of the ions in the solution.
Iron Bacteria
Organisms which are capable of utilizing ferrous iron, either from the water or from steel pipe, in their metabolism and precipitating ferric hydroxide in their sheaths and gelatinous deposits. These organisms tend to collect in pipelines and tanks during periods of low flow and to break loose in slugs of turbid water to create staining, taste and odour problems.
Manganese Greensand
Greensand which has been processed in incorporate in its pores and on its surface the higher oxides of manganese. The product has a mild oxidizing power and is often used in the oxidization and precipitation of iron manganese, and/or hydrogen sulfide and their removal from water.
Mechanical Filtration
The process of removing suspended particles from water by a straining action. The finest mechanical filters can remove bacteria as small as 0.2 microns.
Milligrams per Liter (mg/L)
A unit of concentration of matter used in reporting the results of water analyses. The preferred unit of measure.
A micron (m) is a metric unit of length equal to a millionth of a meter, or 0.00003937 inch. A human hair is approximately 75 m in diameter. The smallest particle that can be seen with the naked eye is 40 m across The smallest bacteria is about 0.22 m while a virus is even smaller at 0.01 m.
Micron Rating
The term applied to a filter or filter medium to indicate the particle size above which all suspended solids will be removed throughout the rate capacity.
A process of diffusion of water through a semipermeable membrane, which will transmit the water, but impede most dissolved substances. The normal flow of water is from the dilute solution to the concentrated solution.
Osmotic Pressure
The pressure created by the tendency of water to flow in osmosis. Every 100 PPM of TDS generates about 1 psi of osmotic pressure. This osmotic pressure must first be overcome by the water pressure for the reverse osmosis membrane to be effective.
A chemical process in which electrons are removed from an atom, ion or compound.
Parts per Million (PPM)
Indicates the number of parts by weight of a dissolved or suspended constituent, by weight of water or other solvent. In dilute water, one PPM is practically equal to one mg/L.
A measure of the intensity of the acidity or alkalinity of water on a scale from 0 to 14, with 7 being neutral.
To cause a dissolved substance to form a solid particle which can be removed by settling or filtering such as in the removal of dissolved iron by oxidation, precipitation and filtration. The term is also used to refer to the solid formed and the condensation of water in the atmosphere to form rain or snow.
Alterations of the raw feed water are required to prevent damage to the reverse osmosis membrane.
Product Water
The pure water that has been separated from the feed water stream by the reverse osmosis membrane.
The amount of product water as compared with the total amount of feed water. This will give a measure of the efficiency of operation.
A solution of a chemical used to restore the capacity of an ion exchange or oxidation system.
Includes backwash, brine and fresh water rinse steps necessary to prepare a water softener exchange bed for service after exhaustion.
The percentage of TDS removed from the feed water. Typically greater than 90% rejection is achieved with reverse osmosis.
Residual Chlorine
Chlorine remaining in treated water after a specified period of contact time to provide protection throughout a distribution system.
Synthetic organic ion exchange material such as the high capacity cation exchange resin widely used in water softeners.
Reverse Osmosis (RO)
A process that reverses, by the application of pressure, the flow of water in the process of osmosis so that the water passes from the more concentrated to the more dilute solution through a semi-permeable membrane.
The sum of particles of dirt, clay, silt and vegetation which float or are suspended in water and can be removed by mechanical filtration.
A term which applies to special materials, both natural and synthetic, which allow certain substances, such as water, to pass through (to permeate) while blocking or rejecting the passage of other substances.
Service (Peak) Flow Rate
The greatest amount of water, in gallons per minute, that a particular filter can effectively process.
Soda Ash
The common name for sodium carbonate, a chemical compound used in the lime soda ash water conditioning process.
Spiral Wound
The most common practical configuration for a reverse osmosis membrane in which sheets with large surface area are wrapped in a spiral fashion to fit in a small space.
A substance resulting from the decomposition of lignin in vegetable matter.
Total Dissolved Solids (TDS)
The weight of solids per unit volume of water which are in true solution.
Trihalomethans (THM's)
A group of suspected carcinogenic organic chemicals formed in water when chlorine reacts with naturally occurring organic matter. One of the most common THM's is chloroform.
Suspended biological, inorganic and organic particles in water which may be in sufficient amount to make the water seem cloudy.
Water Softening
The removal of calcium and magnesium, the ions which are the principal cause of hardness, from water.

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Scott M. Gillespie
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