Glossary of Water Purification Terms

absolute filter rating - Refers to the smallest particle size that a filter will trap 100 percent. For example, a 5-micron absolute filter will trap all particles 5 microns and larger. See nominal filter rating

activated carbon - Carbon that has been specially treated to enhance its ability to trap certain chemicals.

adsorption - The process by which carbon filters trap chemicals.

aeration - The process of exposing water to large amounts of oxygen in order to remove certain kinds of chemicals.

aggressive water - Water that, because of its purity, aggressively reacts (chemically) with materials it contacts.

aquifier - A naturally occurring underground reservoir.

backwashing - Reversing the flow of water through a filter in order to cleanse it of accumulated particulate matter.

CA membrane - Cellulose acetate membrane. A type of membrane used in reverse osmosis.

carcinogen - A substance that causes or contributes to the onset of cancer.

chloramine - A combination of chlorine and ammonia used to disinfect water.

chlorine - a chemical used to disinfect water.

colloid - A tiny particle that remains in suspension in a liquid.

condensate - Water that has been vaporized and then returned to liquid form. Same as distillate.

contact time - The amount of time that water contacts a filter medium while flowing through a filter.

contaminate - A substance in water that is harmful or otherwise undesirable. Same as pollutant.

corrosion - A chemical process by which water attacks metal surfaces and weakens or destroys them.

de-ionization (DI) - A process that removes minerals from water by ion exchange.

disinfection - The process of killing bacteria and other microorganisms in water.

dissolved solids - Particles that have dissolved in water and are in solution. See total dissolved solids.

distillate - Water that has been vaporized by boiling and then returned to liquid form. Same as condensate.

distillation - The process of boiling water, capturing the steam, and cooling it so that purified water is produced.

effluent - The water flow that exits from a device or system.

feed, feedwater - A solution that enters a device or system for a specific purpose, as in a chlorine feeder.

filtrate - In a treatment device, the water flow after it has passed through a filter or membrane.

finished water - Water that has been improved by a water treatment plant and is ready to be delivered to customers.

flocculent - A substance that is added to water to make particles clump together in order to achieve better filtration.

giardia - A microorganism that occurs in water in the form of cysts; a cause of gastrointestinal disorders.

gpm, gph, gpd - The rate of water flow in gallons per minute, per hour, or per day.

ground water - Water whose source is underground.

hardness - The amount of calcium and magnesium in water, which causes it to clean inefficiently.

heavy metals - The toxic metals in water, such as cadium, lead, and mercury.

hydrogen sulfide - A toxic gas in water that smells like rotten eggs.

influent - The water flow input to a device or a system.

ion - An electrically charged atom.

ion exchange - A process by which undesirable ions in water are exchanged for more beneficial ones.

MCL - Maximum contaminant level; the maximum level recommended by federal law for a particular water pollutant.

membrane - A thin material that is porous enough to reject pollutants while allowing pure water to pass through.

mg/1 - Milligrams per liter. A measure of the amount of a substance in water. The equivalent to parts per million.

micron - A shortened term for one micrometer. One millionth of a meter.

mutagen - A substance that causes or contributes to generic mutation.

NDWR - National Drinking Water Regulations, as established by the Safe Drinking Water Act of 1974.

NOC - Naturally occurring organic chemical.

nominal filter rating - Refers to the smallest particle size that a filter will trap most of. For example, a 5-micron nominal filter might trap 95 percent of all particles 5 microns or larger. See absolute filter rating.

oxidizing filter - A filter that removes pollutants from water by chemical reaction.

ozone - A toxic form of oxygen that is used to disinfect water.

particulate - Particles in water.

permeate - That portion of the water that passes through an RO membrane.

pH - The measure of alkalinity/acidity in water. A pH of 1 to 7 is acidic, 7 to 14 is alkaline, and exactly 7 is neutral.

pollutant - A substance in water that is harmful or otherwise undesirable. Same as contaminant.

pore size - This refers to the smallest substance that an RO membrane will reject most of. For example, a .001-micron membrane might reject approximately 90 percent of all substances .001 microns and larger.

PPB - Parts per billion. A measure of the amount of a substance in water. One part per billion is equivalent to one billionth of a gram per liter.

PPM - Parts per million. A measure of the amount of a substance in water. Equivalent to milligrams per liter.

Primary Regulations - National Drinking Water Regulations that pertain to harmful water pollutants.

psi - Pounds per square inch of water pressure.

recovery rate - The ratio of pure water produced to total water used in the process of reverse osmosis.

regeneration - A process by which a filter medium is cleansed of accumulated pollutants, such as by reversing the flow of water through it.

rejection - The process whereby certain substances cannot pass through a membrane and are drained off.

resin - A specially prepared mineral that is used in de-ionization and in some kind of filters.

reverse osmosis (RO) - A process by which contaminants are rejected by a membrane while pure water is allowed to pass through.

scale - A hard, whitish buildup of mineral deposits on surfaces that contact water, such as the inside of water pipes or the boiling chamber of a distiller.

Secondary Regulations - National Drinking Water Regulations that pertain to the aesthetic and convenience qualities of water.

SOC - Synthetic organic chemical.

softness - The quality of water, desirable for efficient cleaning and minimal corrosion, that results from very low amounts of calcium and magnesium.

teratogen - A substance that causes or contributes to birth defects.

TDS - Total dissolved solids. The standard measure of minerals dissolved in water.

TFC membrane - Thin film composite membrane. A type of membrane used in reverse osmosis.

THM - Trihalomethane. A type of toxic chemical, commonly formed when organic chemicals in water combine with chlorine.

turbidity - A measure of the opacity, or cloudiness of water that is caused by particulates.

ultraviolet disinfection (UV) - A process by which intense ultraviolet light is used to kill bacteria and other microorganisms.

VOC - Volatile organic chemical. A class of chemicals that evaporate easily and which can be absorbed through the skin.


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