Glossary of Water Treatment Terminology

Action Level: The level of lead or copper which, if exceeded, triggers treatment or other requirements that a water system must follow.

Activated Carbon: A water treatment medium, found in block, granulated, or powdered form, which is produced by heating carbonaceous materials, such as coal, wood, or coconut shells, in the absence of air, creating a highly porous adsorbent material. Activated carbon is commonly used for dechlorination, organic chemical reduction and radon reduction, and is recognized by the US EPA as the best available technology for reduction of organic chemicals from drinking water.

Acute Health Effect: An immediate (i.e. within hours or days) effect that may result from exposure to certain drinking water contaminants (e.g., pathogens).

Aquifer: A natural underground layer, often of sand or gravel, that contains water.

Alkalinity: The quantitative capacity of water to neutralize an acid; that is, the measure of how much acid can be added to a liquid without causing a significant change in pH. Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have high alkalinity. In the water industry, alkalinity is expressed in mg/l of equivalent calcium carbonate. There are three kinds of alkalinity: carbonate, bicarbonate, and hydroxide alkalinity. Total alkalinity is the sum of all three kinds of alkalinity. Different tests are used to determine the quantity of the different kinds of alkalinities present in water.

Amoeba: A single celled protozoan that is widely found in fresh and salt water. Some types of amoebas cause diseases such as amoebic dysentery.

Automatic water softener (or Automatic Filter): A water softener (or filter) that is equipped with a clock timer, meter, or sensor which automatically initiates the backwash and/or regeneration process at the preset intervals of time. A predetermined number of gallons of water usage or as determined by a sensor. All operations, including bypass of treated or untreated water (depending upon design), backwashing, brining, rinsing, and returning the unit to service are performed automatically.

Bacteria: Unicellular microorganisms which typically reproduce by cell division. Although usually classed as plants, bacteria contain no chlorophyll. Many different types of bacterial organisms are often found in drinking water.

Barrier Layer: This refers to the active layer of membrane material that actually separates the impurities from the product stream or permeate. This barrier layer is supported by a micro-porous support layer, usually made from polysulfone, which is cast on a non-woven support material.

Best Available Technology: The water treatment(s) that EPA certifies to be the most effective for removing a contaminant.

Brine: A strong solution of salt(s), such as the sodium chloride or potassium 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.

Brine Tank: A tank which sits beside the softening unit and acts as a salt storage and brine supply.

Cartridge Filter: Cartridge filters are a widely used and have been utilized for water treatment for many decades. Cartridges are usually rated in microns. 40 microns is considered the largest particle visible to the human eye. Typical prefiltration requirements for reverse osmosis systems are around 5 microns.

Chemical Feeder: A mechanical device designed to introduce chemicals into a water system, more or less accurately in proportion to water flow.

Chlorinator: A mechanical device specifically designed to feed chlorine gas or pellets, or solutions such as hypochlorides, into a water supply in proportion to the flow of water.

Chronic Health Effect: The possible result of exposure over many years to a drinking water contaminant at levels above its MCL.

Coliform Bacteria: A group of related bacteria whose presence in drinking water may indicate contamination by disease-causing microorganisms.

Community Water System: A water system which supplies drinking water to 25 or more of the same people year-round in their residences.

Contaminant: Anything found in water (including microorganisms, minerals, chemicals, radionuclides, etc.) which may be harmful to human health.

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

Cryptosporidium: A microorganism commonly found in lakes and rivers which is highly resistant to disinfection. Cryptosporidium has caused several large outbreaks of gastrointestinal illness, with symptoms that include diarrhea, nausea, and/or stomach cramps. People with severely weakened immune systems (that is, severely immuno-compromised) are likely to have more severe and more persistent symptoms than healthy individuals.

Cycle: A complete course of ion exchange operation. For instance, a complete cycle of cation exchange would involve: regeneration of the resin, rinse to remove excess regenerant, exhaustion, backwash, and finally regeneration again.

Dealkalization: A process for the reduction of alkalinity in a water supply. It is generally accomplished by a chemical feed processor combined cation and anion exchange systems.

Dechlorination: The removal of excess or free chlorine from a water supply by adsorption with activated carbon or by catalytic type filter media.

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).

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.

Disinfectant: A chemical (commonly chlorine, chloramine, or ozone) or physical process (e.g., ultraviolet light) that kills microorganisms such as bacteria, viruses, and protozoa.

Distribution System: A network of pipes leading from a treatment plant to customers’ plumbing systems.

Feed Water: This refers to the incoming water of a water treatment system that has not yet been treated. Also called raw water or source water.

Filter: A device used to clean water by removing iron, silt, taste, odor, color, etc., before it is fed into the softener or supply lines of the consumer. Includes mechanical, adsorptive, oxidizing and neutralizing filters. Available as media beds in tanks or as cartridge type devices.

Filtration: The process of passing water through a porous substance to remove solids in suspension. Available as media beds in tanks or as cartridge type devices.

Flow Rate: The volume of solution which passes through a given quantity of resin within a given time. Flow rate is usually expressed in terms of gallons per minute per cubic foot of resin, or as milliliters per minute per milliliter of resin. If the flow rate is greater than it should be, the water will not be completely softened or filtered.

Giardia lamblia: A common protozoan found in water and is derived from animal droppings. It can cause contagious waterborne disease characterized by acute diarrhea. It is resistant to disinfectants such as chlorine, iodine, or ultraviolet light. Giardia can be removed by filters of four micron rating. (Click for information about reverse osmosis)

Greensand: A natural mineral, primarily composed of complex silicates, which possess ion exchange properties. Greensand was the original material used in domestic and commercial water softeners and is the base product in the production of manganese greensand.

Ground Water: The water that systems pump and treat from aquifers (natural reservoirs below the earth’s surface). The term describing all subsurface water and the source of well water. It can be found in aquifers as deep as several miles.

Hardness: 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 soaps. Hardness is usually expressed in grains per gallon, parts per million, or milligrams per liter, all as calcium carbonate equivalent. Temporary hardness, caused by the presence of magnesium of calcium bicarbonate, is so called because it may be removed by boiling the water to convert the bicarbonates to the insoluble carbonates. Calcium sulfate, magnesium sulfate, and the chlorides of these two metals cause permanent hardness.

Hard Water: Water with a total hardness of one grain per gallon or more, as calcium carbonate equivalent.

Influent: The water entering a water treatment device.

Inorganic Contaminants: Mineral-based compounds such as metals, nitrates, and asbestos. These contaminants are naturally-occurring in some water, but can also get into water through farming, chemical manufacturing, and other human activities. EPA has set legal limits on 15 inorganic contaminants.

Inorganic Matter: Matter which is not derived from living organisms and contains no organically produced carbon; includes rocks, minerals and metals.

Ion: An atom, or group of atoms in a solution which function as a unit, and has a positive or negative electrical charge, due to the gain or loss of one or more electrons. It is smaller than a colloid.

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 concentration of the ions in the solution. The ion exchanger media is an insoluble permanent solid medium. for a product offering.

Ionization: The dissociation of molecules into simpler, electronically charged particles. It is related to the gaining or losing of electrons causing the atoms to become electronically charged.

Lime: The common name for calcium oxide (CaO); hydrated lime is calcium hydroxide, Ca(OH)2.

Lime Scale: Hard water scale containing a high percentage of calcium carbonate. Insoluble scale is commonly formed when water containing calcium carbonate is heated. It also forms in cold water but precipitates at a higher pH.

Manganese: A element sometimes found dissolved in ground water, usually with dissolved iron but in lower concentrations. It causes black stains in laundry and plumbing fixtures at concentrations higher than 0.05 mg/l. It is removed the same way as iron, by ion-exchange or oxidation and filtration.

Maximum Contaminant Level (MCL): The highest level of a contaminant that EPA allows in drinking water. MCLs ensure that drinking water does not pose either a short-term or long-term health risk. EPA sets MCLs at levels that are economically and technologically feasible.

Maximum Contaminant Level Goal (MCLG): The level of a contaminant at which there would be no risk to human health. This goal is not always economically or technologically feasible, and the goal is not legally enforceable.

Mechanical Filter: A filter primarily designed for the removal of suspended solid particles, as opposed to filters that remove contaminants by chemical means.

Media (or Multi-Media) Filter: Also called depth filters. A variety of media types may be employed in this type of filtration device, depending on the objective of this part of the water treatment system. Sand has been employed in this type of filter for many decades. Media type filters are recommended for applications where large quantities of suspended particles need to be removed economically. Usually the media is permanent, so maintenance costs are very low. The device is typically designed with graded media beds, arranged according to size. The spaces between the particles of sand or other media determine the size of particles that will be removed. The depth of the filter base is also a critical design criteria. Water flows downward through a distributor, through the graded media beds, and is collected by another set of distributors installed in the bottom of the tank. The particles are left behind in the media beds. Cleaning is accomplished by backwashing, or reversing the flow. This flow lifts the media beds and dislodges the particles trapped there. These are then washed away with the backwash fluid and discharged. Media filters are often employed as one of the first parts of the pretreatment system in membrane type water treatment systems. Usually, additional filtration afterwards is also required, as the particle size removed by media filters is not small enough to provide good membrane protection.

Membrane: The term membrane generally refers, not only to the barrier layer described above that is technically the membrane, but also to the entire engineered membrane separation device, including the micro-porous support, the non-woven support material, the carriers, product tube, anti-telescoping device, and the construction of the element. The most commonly used membrane element type is a spiral wound membrane element.

Micro-Filtration: This is also a membrane based fluid treatment technology, employing all the parameters of other membrane technologies, but with a larger pore size. Operating parameters are similar to those for U/F, but pore sizes are larger.

Micron: A linear measure equal to one millionth of a meter, or .00003937 inch. The symbol for the micron is the Greek letter “ƒÊ”. The smallest particle visible to the human eye is 40 microns. Most types of bacteria range from 0.05 to 10.0 microns in size.

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 rated capacity. As used in industry standards, this is an “absolute”, not “nominal” rating.

Microorganisms: Tiny living organisms that can be seen only with the aid of a microscope. Some microorganisms can cause acute health problems when consumed in drinking water. Also known as microbes.

Mineral: A term applied to inorganic substances, such as rocks and similar matter found in the earth’s strata, as opposed to organic substances such as plant and animal matter. Minerals normally have definite chemical composition and crystal structure. The term is also applied to matter derived from minerals, such as the inorganic ions found in water. The term has been incorrectly applied to ion exchangers, even though most of the modern materials are organic ion exchange resins.

Nano-Filtration (N/F): Nano-Filtration is a membrane based treatment method with lower rejection rates than R/O. Nano-Filtration is often employed as a water softening device because it typically rejects larger molecules (such as those that cause scaling and water hardness) very well, but smaller molecules are usually allowed to pass. Nano-Filtration systems thus usually operate at a lower pressure than similar reverse osmosis systems, and reject less of the dissolved solids. This technology is frequently employed in waste water treatment systems. Nano-Filtration systems can often operate at higher recovery rates than R/O systems.

Operating Pressure: The range of pressure, usually expressed in pounds per square inch, over which a water conditioning device or water system is designed to function. Usually 30-100 psi.

Organic Contaminants: Carbon-based chemicals, such as solvents and pesticides, which can get into water through runoff from cropland or discharge from factories. EPA has set legal limits on 56 organic contaminants.

Osmosis: A process of diffusion of a solvent such as water through a semi-permeable membrane which will transmit the solvent but impede most dissolved substances. The normal flow of solvent is from the dilute solution to the concentrated solution. Osmosis causes the stronger solution to become more diluted and tends to equalize the opposing solutions.

Osmotic Pressure: This is the pressure differential that develops as a result of a solution containing water and a particular concentration of dissolved solids, including minerals and salts. The osmotic pressure must be exceeded to produce purified water by means of reverse osmosis. Tap water may have an osmotic pressure of about 10 PSI (1 Bar), while seawater may have an osmotic pressure of around 376 PSI (27 Bar) or more. To produce a suitable quantity of product water, reverse osmosis systems typically operate at more than double the osmotic pressure.

Oxidizing Filter: A type of filter used to change the valence state of dissolved molecules, making them insoluble and therefore filterable. For example, a filter that oxidizes ferrous iron, manganous manganese, and/or anionic sulfur by use of a catalytic media such as manganese oxide and then filters the oxidized precipitant out of the water.

Particulate: A term used to describe visible sediment particles, used as both singular and plural.

Parts per Billion / ppb: A basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of a dissolved or suspended constituent, per billion parts by weight of water or other solvent. One part per billion is equal to one microgram per liter, the preferred unit.

Parts per Million / ppm: A common basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of water or other solvent. In dilute water solutions, one part per million is practically equal to one milligram per liter, which is the preferred unit. 17.l ppm equals one grain per US gallon. One ppm equals one pound per million pounds of water.

Pathogen: A disease-causing organism.

Permeate: This is a term used to refer to the water produced by a membrane process. The permeate is the water that permeates or penetrates through the membrane as product water.

pH (potential of Hydrogen): An expression of the acidity of a solution; the negative logarithm of the hydrogen ion concentration (pH 1 very acidic; pH 14, very basic; pH 7, neutral). e.g., pH 5 is 10 times the acidity of 6 and 100 times the acidity of 7. pH is a measure of intensity and not capacity. It is the logarithm of the reciprocal of the hydrogen ion concentration of a solution. The neutral point of 7 indicates the presence of equal concentrations of free hydrogen and free hydroxide ions.

Point of Entry: A water treatment device which installs at the main inlet to a building and acts as centralized treatment.

Point of Use: A water treatment system designed to connect at the actual point-of-use for water; countertop or under-sink treatment systems.

PPM (Parts per Million): This measurement is a means of specifying the concentration of any constituent in a solution of water. This is the same as mg/l or milligrams per liter.

Pressure Vessel: Membrane elements must be installed in a pressure vessel to provide the means to supply feed water, remove the reject or concentrate stream, delivery product water, and contain the pressure at which membrane systems much operate.

Pre-Treatment: Membrane type water treatment systems require good pretreatment to ensure optimum system performance and acceptable membrane life. Pretreatment always includes one or more types of prefiltration.

Product Water: This is the term used to describe the treated or purified water produced by a water treatment system, including reverse osmosis systems and others. Also known as Permeate.

Protozoa: Any of a large group of mostly microscopic, one celled animals living chiefly in water. Many protozoa’s are parasitic and are higher on the food chain than the bacteria they eat.

Radionuclides: Any man-made or natural element that emits radiation and that may cause cancer after many years of exposure through drinking water.

Raw Water: Water in its natural state, prior to any treatment for drinking. Untreated water from wells or from surface sources or any water before it reaches a water treatment device or process.

Regeneration: The process of returning the sodium ions to the mineral after it has exchanged all its sodium ions for calcium and magnesium from hard water. This is accomplished by first back-washing the mineral bed to free it of all foreign matter, them passing salt brine through the mineral. The sodium ions attach themselves to the mineral, and the calcium and magnesium combine with the chloride from the brine to form calcium and magnesium chlorides, which are rinsed down the drain. All water softeners using the ion-exchange process are regenerated with these basic steps. In similar fashion cation and anion components of a demineralizer as well as manganese greensand are recharged with comparable sequences.

Reject: The reject stream is the water that does not pass through the membrane. Since minerals are left behind from the departed permeate or product water, the reject stream is more concentrated than the source or feed water. Hence it is also called the concentrate.

Rejection Rate: This figure, typically 80% to 99.5%, indicates the percentage of dissolved solids that will be rejected, or prevented from passing through with the product water, using the reverse osmosis drinking water systems.

Resin: Synthetic organic ion exchange material, such as the high capacity cation exchange resin widely used in water softeners. Technical name- sulfonated co-polymer of styrene and divinyl benzene.

Reverse Osmosis (R/O): A water treatment process utilizing a membrane to remove dissolved minerals. The process of osmosis occurs in nature, when a pure solution is separated from a saline solution by a semi-permeable membrane. The pure solution passes through the membrane until a pressure differential is reached called the Osmotic Pressure. At this pressure differential, determined by the constituents and concentrations in the saline solution, osmosis stops. Reverse Osmosis reverses this process by applying pressure in excess of the osmotic pressure to the saline solution, forcing water through the membrane. As this occurs, most dissolved solids remain behind and are carried out with the reject stream. The purified water can then be utilized as needed.

Softened Water: Any water that is treated to reduce hardness minerals to 1.0 GPG (17.1 mg/L) or less, expressed as calcium carbonate.

Sole Source Aquifer: An aquifer that supplies 50 percent or more of the drinking water of an area.

Solvent: The liquid, such as water, in which other materials (solutes) are dissolved.

Source Water: Water in its natural state, prior to any treatment for drinking.

Sub-Micronic Filtration: Sub-micronic filtration technology is usually applied using more conventional filtration media, but with very small pore sizes. Membranes are usually not used for this technology. Rather, cartridge filters are employed.

Surface Water: The water that systems pump and treat from sources open to the atmosphere, such as rivers, lakes, and reservoirs.

TDS (Total Dissolved Solids): This is a measure, usually given in PPM (Parts Per Million) or in milligrams per liter (mg/l) that is used to specify the concentration of all minerals dissolved in a water solution. This measurement is a principle factor in determining the Osmotic Pressure of a solution and hence the operating pressure necessary for a system to produce a reasonable amount of product water.

Total Hardness: The sum of all hardness components in a water, expressed as their equivalent concentration of calcium carbonate. Primarily due to calcium and magnesium in solution, but may include small amounts of metals such as iron which can act like calcium and magnesium in certain reactions. These minerals are scale forming, affect taste and color of certain foods and react with soap to form insoluble soap curds.

Treatment: A required process intended to reduce the level of a contaminant in drinking water.

Turbidity: The cloudy appearance of water caused by the presence of tiny particles. High levels of turbidity may interfere with proper water treatment and monitoring. A measure of the amount of finely divided suspended matter in water, which causes the scattering and adsorption of light rays. Turbidity is usually reported in arbitrary nephalometric turbidity units (NTU) determined by measurements of light scattering. NTU should not exceed 0.5 in potable water. Turbidity can protect bacteria from sterilization.

Ultra-Filtration (U/F): Ultra-Filtration is another membrane based treatment system which does not usually reject molecules except for very large ones, but rejects virtually all particles. This technology is often used to remove suspended solids from feed streams before feeding the water or other fluid to the reverse osmosis or nano-filtration membranes. This can be very effective when the suspended solids load is unusually heavy or when oil or grease is present. Ultra-Filtration can also be effectively employed as a means to remove bacteria. U/F systems can usually achieve high recovery rates, as no dissolved solids are rejected. U/F can be very effective in oil removal or concentration.

Watershed: The land area from which water drains into a stream, river, or reservoir.

Wellhead Protection Area: The area surrounding a drinking water well or well field which is protected to prevent contamination of the well(s).

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