Glossary of Water Terms: A Helpful Guide to Water Terminology

A close up of water droplets on a blue surface.

Glossary of water terms

Here’s a comprehensive, non-technical glossary of water terms to help you better understand water treatment and terminology concerning water related issues. We’ve tried to break things down to make them as easy to understand as possible. If you need help finding the best water treatment solution for you, please give us a call on (760) 282-4668.

Glossary of water terms, A to Z

Absolute / Absolute Filter Rating. Refers to the micron rating of water filter cartridges. It’s the exact size of particles that will be trapped on or within the water filter cartridge. For example, a one micron absolute filter will trap all particles larger than one micron.

Absorption. The process in which one substance absorbs or is absorbed by another. An example of absorption in water treatment is when undesirable contaminants are removed by absorption into or on the filter medium.

Acid. A substance which releases hydrogen ions when dissolved in water, has a pH rating lower than 7.0 (it will turn litmus paper red, and tastes sour), and is the opposite of an alkali.

Acidity. The level of acid in water.

Activated Carbon. The best available technology (according to the EPA) to remove tastes, odor, chlorine, chloramines and some organics from water. Activated carbon can be in block, granulated, or powdered form. It’s a highly porous, adsorbent material so is commonly used to filter harmful contaminants from contaminated water.

Aeration. The process of adding air (or oxygen) to a water supply for the purpose of oxidation. Aeration is frequently used to remove iron, carbon dioxide, and hydrogen sulphide from water.

Air Gap. A plumbing device designed to provide a siphon break for the drain line of an under sink reverse osmosis unit. It prevents the reverse flow of water from the wastewater into the water supply system. Without an air gap, there is an increase in the pressure in the wastewater system causing a creation of a negative pressure in the water supply line and reverse flow of water. It is recommended that the air gap be twice the diameter of the inlet (minimum width of 1 1/2 inches).

Aggressive Water. Water containing acid or oxygen which speeds up corrosion (rusting). It is recommended to use a water filter with corrosion and scale inhibitor product such as Siliphos (Premiere Sales is the only water treatment company to provide this triple-style method of water filtration for preventing corrosion).

Algae. Plant-like organisms which grow in water (green scum).

Alkali. A substance which has a pH greater than 7.0 (it will turn red litmus paper blue) and is the opposite of an acid. It creates a bitter taste, has a slippery feel when dissolved in water, and highly alkaline water causes dry skin. Alkalis may include the soluble hydroxide, carbonate, and bicarbonate salts of calcium, magnesium, potassium, and sodium.

Acid. A substance which releases hydrogen ions when dissolved in water, has a pH rating lower than 7.0 (it will turn litmus paper red, and tastes sour), and is the opposite of an alkali.
Alkalinity . The level of alkalis in water.

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

ANSI. Abbreviation for American National Standards Institute.

Aquifer. An underground geological formation containing water that supplies water for wells and springs such as water-bearing permeable rock, rock fractures, or unconsolidated materials.

Automatic Water Softener / Automatic Filter. A water softener or filter with a clock timer, meter, or sensor which automatically starts the backwash and/or regeneration process at predetermined intervals of time.

Backflow. When water in a pipe or line flows in the opposite direction opposite to normal. This is often due to back siphonage or the flow of contaminated water into a potable water system.

Backwash. Reverse solution flow through a system. Backwashing cleans and resettles the filter bed.

Bacteria. Unicellular microorganisms. Some bacteria are helpful, others harmful. There are many different types of bacteria found in drinking water.

Bactericide. A substance or agent that kills bacteria.

Balanced Water. Water that has a pH of zero and is neither corrosive nor scaling.

Bed. A mass of ion exchange resin particles or filter media contained in the column of a water filter or membrane.

Binders. Chemicals used to hold, or bind, short fibers together in a water filter cartridge.

Blinding. The fouling or plugging of pores in a water filter membrane.

Brackish Water. Water that has more salinity than fresh water, but not quite as much as seawater. Brackish water typically contains more bacteria (anything between 1.000 and 15,000 ppm of dissolved solids).

Brine. Water with a high concentration of salt.

Bromine. Chemical sanitizer that kills bacteria and algae.

Buffer. Chemical that resists pH change.

Bypass. A connection or a valve system that allows untreated water to flow to a water system while a water softener or filter regenerates, backwashes, or is being serviced. It can also refer to a special water line installed to provide untreated water to a particular tap (i.e., a sill cock).

Calcium Hardness. A measure of the calcium salts dissolved in water.

Chemical Feeder. A mechanical pump used to meter chemicals such as chlorine or polyphosphate into a water system.

Chloramine. A combination of chlorine and ammonia that is used to disinfect many municipal water supplies. It is more difficult to remove from water than free chlorine.

Chlorine . A very toxic biocide that is widely used in the disinfection of water to kill bacteria and algae.

Coliform Bacteria. A group of organisms primarily found in human and animal intestines and wastes that can end up in water and cause disease.

Colloid. Material of very fine particle size, typically between 0.1 and 0.001 microns in diameter.

Compaction. Decline in flux (the rate at which water permeates a reverse osmosis membrane) as a result of applied pressure compressing a reverse osmosis or ultrafiltration membrane.

Concentrate. The rinse water from a reverse osmosis unit.

Contact Time (or Retention Time). In reference to a water treatment system, the time that water remains in contact with an oxidizer, regenerant, or water conditioner. Contact time determines the effectiveness of a water treatment system.

Contaminant. Any physical, chemical, biological or radiological substance in water which reduces the quality of the water.

Corrosion. The destructive disintegration of metals by contaminants in the water.

Dechlorination. The removal of chlorine from a water supply by adsorption with activated carbon or other filter media.

Deionization (DI). Uses ion exchange resin to remove salts from water.

Demineralization. The process of removing minerals from water. Deionization, reverse osmosis and distillation are water treatment processes that remove minerals from water.

Disinfection. Destroying bacteria in a water supply.

Distilled Water. A type of purified water in which water has been boiled into steam and condensed back into liquid in a separate container. Contaminants in the original water that do not boil remain in the original container resulting in pure, distilled water.

Drain Line. A pipe from a water treatment system used to carry backwash water, regeneration wastes and/or rinse water to a drain or waste system.

Drinking Water Standards. As established by the U.S. Environmental Protection Agency (EPA), drinking water must be ‘wholesome’ and  there are maximum contaminant levels (MCL’s) for regulated substances in drinking water.

DWV. Abbreviation for Drainage, Waste, and Vent in reference to pipes.

Effluent. The outflow of a water treatment device. May also refer to the product water from a water conditioning system.

Exhaustion. When a water filter cartridge is no longer capable of the removal of a specific pollutant.

Feed. The input solution to a system.

Filter. A device used to clean water by removing contaminants.

Filtration. The process of passing water through a porous device to remove solids including contaminants.

Fines. Particles smaller than the specified size of filtration materials. An excess of fines can create undesirable pressure drop in the system. It’s not uncommon for carbon fines, for example, to be present in a new GAC filter when it is first installed (the carbon fines are small gray or black suspended solids).

Fixture Count. The total number of plumbing fixtures in a building. It’s used to estimate flow rates and sizes for water filtration equipment.

Flow Rate. The volume of liquid which passes through a given filter within a given time. Flow rate is usually expressed in terms of gallons per minute. If the flow rate is greater than it should be, the water may not be completely filtered.

Flux. The rate at which water goes through a reverse osmosis membrane. It is usually expressed in volume per unit time, such as “GPD”.

GPD. Gallons per day.

GAC. Granular activated carbon. A water filtration option that removes certain chemicals, particularly organic chemicals, from water as well as offensive odors or tastes and chlorine.

GPG. Grains per gallon. A common measurement for water hardness. Equal to 17.1 parts per million.

Ground Water. The term describing all subsurface water. Well water, in other words. It can be found in aquifers as deep as several miles.

Hardness. The concentration of calcium and magnesium salts in the water. Water hardness is responsible for most scale formation in pipes and water heaters. Hardness is usually expressed in grains per gallon, parts per million, or milligrams per liter, all as calcium carbonate equivalent.

Hard Water. Hard water is water that has high mineral content (one grain per gallon or more, as calcium carbonate equivalent). Hard water is formed when water goes through deposits of limestone and chalk which has a high level of calcium and magnesium carbonates.

Heavy Metals. Metals having a high density or specific gravity. A generic term used to classify contaminants such as cadmium, lead and mercury.

Hydrogen Sulfide. A corrosive and flammable gas produced from decaying organic matter, that is detectable by a strong “rotten egg” odor.

Influent. The water entering a water treatment system.

In-parallel Flow. When pipes are arranged so that there are separate streams going through two or more water treatment units. There is  equal flow to each device. The inlets of two or more units are connected together, and the outlets are connected together producing a simultaneous flow through each unit.

In-series Flow. When pipes are arranged so that the output flow of one unit in a water treatment system is fed to a second unit. The purpose of this is to filter out more contaminants than a single unit alone.

Ion Exchange. A chemical reaction in which ions are exchanged in solution. Deionization and a water softener are common examples of ion exchange.

Iron Fouling. When too much iron accumulates in a filter bed resulting in a reduced capacity of the media.

Langelier Index. A mathematically-derived factor indicator of the degree of saturation of calcium carbonate in water. It takes into consideration calcium hardness, total alkalinity, and pH at a given temperature. A Langelier Index of zero indicates perfect water balance- that is, water that is neither corroding nor scaling.

Lime. A white caustic alkaline substance consisting of calcium oxide.

Lime Scale. Hard water scale containing a high percentage of calcium carbonate. It’s a hard, off-white, chalky deposit.

Magnesium Hardness. A measure of the magnesium salts dissolved in water. It is not considered in regards to water balance.

MCL. Maximum Contaminant Level. The maximum amount of a contaminant allowed in drinking water – it’s a drinking water standard.

Membrane. Thin sheets of material that are able to separate contaminants based on properties such as size or charge. A semipermeable membrane is used in such water filtration processes as reverse osmosis, ultrafiltration and microfiltration.

Micron. A linear measure equal to one millionth of a meter and the most common measurement of filter size.

Micron Rating. Indicates the particle size above which all suspended solids will be removed.

Mineral. A term applied to inorganic substances and ions found in water.

Module. In regards to a water filtration membrane, the membrane element and membrane element housing.

Nanofiltration. A type of water filtration that can remove particles in the 300 to 1,000 molecular weight range. It is used most often for water with low total dissolved solids (such as surface water and fresh groundwater), with the purpose of softening and removing natural and synthetic organic matter.

Nephelometric Turbidity Unit (NTU).The standard unit of measurement used to measure turbidity in water. Turbidity is the cloudiness of water caused by large numbers of individual particles. NTU uses a light scattering effect of fine suspended particles in a light beam. How much light reflects for a given amount of particulates is dependent upon properties of the particles like their shape, color, and reflectivity. The NTU has replaced the Jackson Turbidity Unit (JTU) as the standard of measurement.

Nominal / Nominal Filter Rating. Refers to the micron rating of water filter cartridges. It’s the approximate size particles that will be trapped on or within the water filter cartridge. For example, a nominal one micron filter is one that gets most of the particles larger than one micron. See also Absolute.

NSF. Abbreviation for National Sanitation Foundation which tests and certifies products to standardized sanitation and food safety requirements.

Operating Pressure. The range of pressure that a water system is designed to function (usually 30-100 psi). Expressed as pounds per square inch (PSI).

Osmosis. The spontaneous flow of water from a less concentrated solution to a more concentrated solution through a semipermeable membrane. Osmosis causes the stronger solution to become more diluted.

Osmotic Pressure. Measurement of the potential energy difference between the solutions on either side of a semipermeable membrane.

Oxidizing Filters. Filters that use a catalytic media to change the valence state of dissolved molecules, making them insoluble and therefore able to be filtered.

Ozone. A form of oxygen used to disinfect water.

Particulate. Small, visible particles.

Permeable. Allowing some material to pass through.

Permeate. The portion of the feed stream that passes through the membrane. For example, in regards to a reverse osmosis unit, “product water” (the finished water that you drink) is a permeate.

pH (Potential of Hydrogen). A measure of the acidity of water. The pH scale runs from 0 to 14 with pH 0 = very acidic; pH 7 = neutral; pH 14= very basic (alkaline).

Pharmaceutical Grade Water The definition of six grades of water by the U.S. Pharmacopoeia is as follows: 1.) Purified water 2.) Water for injection 3.) Bacteriostatic water for injection 4.) Sterile water for inhalation 5.) Sterile water for injection 6.) Sterile water for irrigation.

POE. Point of entry. A water treatment system installed at the main inlet to a building and acts as centralized water treatment.

Pore. An opening in a membrane which allows certain components to pass through, but not others.

Porous. A material which allows certain substances to pass through its pores.

POU. Point of use. A water treatment system designed to connect at the actual point-of-use for water such as a countertop or undersink water treatment system.

PPB. Parts per billion.

PPM. Parts per million.

Pressure Drop. A decrease in water pressure during its flow. This may be due to internal friction between molecules of water, and external friction due to irregularities or roughness in surfaces past which the water flows.

PSI. Pounds per square inch (pressure).

Raw Water. Unfiltered, unsterilized, untreated water from wells or other sources. Raw water can be extremely dangerous, please read about raw water.

Rejection. Material not being allowed to pass through a membrane. For example, in a reverse osmosis unit, it “rejects” contaminants and does not allow them to enter the permeate, or product water.

Resin. Synthetic organic ion exchange material used to remove dissolved salts from water.

Reverse Osmosis. A process for the removal of dissolved solids from water, in which pressure is used to force the water through a semi-permeable membrane, which will accept the water but reject any other contaminants and dissolved materials. It is called reverse osmosis because mechanical pressure is used to force the water to flow in the direction that is the reverse of natural osmosis. Reverse osmosis is a popular and effective drinking water treatment that purifies water.

RO.The abbreviation for reverse osmosis.

Scale. Crust of calcium carbonate. Scale can build-up in pipes or the interior of appliances like hot water heaters.

Semipermeable. Allowing certain size material to pass through a membrane while rejecting other size material. A reverse osmosis unit uses a semipermeable membrane.

Soft Water. Any water that is treated to reduce hardness minerals to less than 17 PPM, expressed as calcium carbonate.

Solute. Dissolved particles in a solvent.

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

Superchorination. Administering large amounts of chlorine to destroy build-up of undesirable compounds in water.

Suspended Solids. Small, solid particles which are suspended in water. It is used as an indicator of water quality.

Thin-film Composite Membrane (TFC). A reverse osmosis membrane resistant to bacteria and can withstand a wide pH range. Do not use with chlorine.

Total Dissolved Solids. The accumulated total of all solids that might be dissolved in water.

Turbidity. Turbidity is the cloudiness of water caused by a large numbers of individual particles. It can look like mud,stirred-up sediment, silt, clay, etc.

Ultrafiltration. A membrane type system that removes very small particles in size range between 0.002 to 0.1 microns.

Ultraviolet Disinfection. The use of ultraviolet light to destroy bacteria.