Glossary of Water Purification Termsabsolute 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.