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About SPU
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Water System
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Water Quality & Treatment
Glossary of Drinking Water Terms
ammonia
A chemical that can be used with chlorine to disinfect water. Not currently used by Seattle Public Utilities.
aquifer
An underground geologic formation capable of storing water. Seattle Public Utilities uses an aquifer know as Highline wellfield to supplement summer demands when necessary.
bacteria
Single-celled micro-organisms that have the potential to cause disease in humans.
chloramination
Treating drinking water by applying chlorine before or after applying ammonia. Not currently used by Seattle Public Utilities.
chlorine
A chemical which destroys small organisms in water. Currently Seattle Public Utilities' secondary disinfectant.
chloroform
A volatile organic compound. One of the four compounds constituting trihalomethanes. See “disinfection by products,” below.
coliform
A group of bacteria commonly found in the environment. They are an indicator of potential contamination of water. Adequate and appropriate disinfection effectively destroys coliform bacteria.
contaminant
Any natural or man-made physical, chemical, biological, or radiological substance or matter in water, which is at a level that may have an adverse effect on public health, and which is known or anticipated to occur in public water systems.
Cryptosporidium
A disease-causing parasite, resistant to chlorine disinfection. Refer to Cryptosporidium page for more information.
disinfection by-products (DBPs)
A group of chemicals that can form in drinking water when chlorine or other disinfectant reacts with the naturally occurring organic matter. Examples of DBPs are haloacetic acids and trihalomethanes.
distribution system
The network of pipes, pumps, and storage facilities used to deliver drinking water the residential and business customers.
E. coli
Escherichia coli is a bacterium commonly found in the human intestine. For water quality analyses purposes, it is considered an indicator organism. These are considered evidence of water contamination. Indicator organisms may be accompanied by pathogens, but do not necessarily cause disease themselves.
enterovirus
A virus whose presence may indicate contaminated water; a virus which may infect the gastrointestinal tract of humans.
fecal coliform
A group of bacteria that may indicate the presence of human or animal fecal matter in water.
filtration
A series of processes that physically removes particles from water.
Seattle Public Utilities constructed a filtration facility on the South Fork Tolt River supply in 2000.
finished water
Treated drinking water that meets state and federal drinking water regulations.
Giardia lamblia
A microscopic protozoan which, when ingested, can cause giardiasis.
giardiasis
A gastro-intestinal disease manifested by diarrhea, fatigue, and cramps.
headworks
The facility at the "head" of the water source where water is first treated and routed into the distribution system.
haloacetic acids (HAAs)
A group of disinfection by products. The major haloacetic acids are: mono-, di-, and trihaloacetic acids, and mono- and dibromoacetic acids.
hardness
The sum of polyvalent cations present in water, expressed as an equivalent quantity of calcium carbonate (CaCO3). The most common such cations are calcium and magnesium.
heterotrophic plate count bacteria
A broad group of bacteria including non-pathogens, pathogens, and opportunistic pathogens; they may be an indicator of poor general biological quality of drinking water.
maximum contaminant level (MCL)
The highest level of a contaminant that is allowed in drinking water by federal or state regulations. If the MCL is exceeded, the water system must treat the water so that it meets the MCL.
maximum contaminant level goal (MCLG)
The level of a contaminant in drinking water below which there is no know or expected risk to human health.
microbe, microbial
Any minute, simple, single-celled form of life, especially one that causes disease.
mg/L, milligrams per liter.
1 mg/L is equal to 1000 micrograms per liter (ug/L). For aqueous (water) samples 1 mg/L is equal to 1 part per million (ppm).
mL
Milliliter, equal to one thousandth of a liter.
nitrates
A dissolved form of nitrogen found in fertilizers and sewage by-products which may leach into groundwater and other water sources.
Nitrates may also occur naturally in some waters. Over time, nitrates can accumulate in aquifers and contaminate groundwater.
NTU (nephelometric turbidity unit)
A measure of the clarity of water.
ozone
A very powerful oxidant which destroys small organisms in water, including Cryptosporidium. Seattle Public Utilities has constructed a filtration and ozonation facility on the South Fork Tolt River supply. Seattle Public Utilities is constructing an ozonation and ultraviolet disinfection facility on the Cedar River supply (expected to be operational in 2004).
pathogens; disease-causing pathogens; waterborne pathogens
A pathogen is a bacterium, virus or parasite that causes or is capable of causing disease. Pathogens may contaminate water and cause waterborne disease.
ppm, part per million.
One ppm is equal to 1000 ppb.
pCi/L, picocuries per liter
A curie is the amount of radiation released by a set amount of a certain compound. A picocurie is one quadrillionth of a curie.
pH
A measure of the acidity or alkalinity of water.
potable water
Water that is safe to drink.
primacy agency
The agency authorized by law to enforce drinking water regulations.
In Washington, the U.S. Environmental Protection Agency has delegated enforcement authority to the Washington State Department of Health, Division of Drinking Water (see links below).
raw water
Water that has not been treated in any way; it is generally considered to be unsafe to drink.
reservoir
An impoundment used to store water. Seattle Public Utilities' water system has six open distribution reservoirs currently in service. Two more open reservoirs are out of service for covering. Seattle has an open reservoir covering program approved by the Washington State Department of Health.
standpipe
A water tank that is taller than it is wide.
surface water
Water which is open to the atmosphere and subject to surface runoff; generally, lakes, streams, rivers. Seattle Public Utilities' surface water supplies are the Tolt and Cedar Rivers.
treated water
Disinfected and/or filtered water served to water system customers. It must meet or surpass all drinking water standards to be considered safe to drink.
Trihalomethanes (THMs)
A group of disinfection-by-products consisting of four separate compounds: chloroform, dichlorobromomethane, dibromochloromethane, and bromoform. The MCL for trihalomethanes is based on a continuous averaging of four quarters of sampling.
turbidity
A measure of the cloudiness of water caused by suspended particles. Measured in Nephelometric Turbidity Units (NTU).
µg/L Micrograms per liter.
For aqueous (water) samples 1 µg/L is equal to one part per billion (ppb).
ultraviolet disinfection
A water treatment process that uses a photochemical reaction to alter the molecular structure of microorganisms in the water, resulting in their injury or death.
valve
A device that opens and closes to regulate the flow of liquids. Faucets include valves.
watershed
An area which drains all of its water to a particular water course or body of water. See the link below for information on Seattle Public Utilities' watersheds.
water works
All of the pipes, pumps, reservoirs, dams and buildings that make up a water system.
Related links
Water Quality Laboratory
Water Quality Planning and Engineering
Water Quality Annual Reports
Water Quality Analyses
Cryptosporidium
Giardia
Water Sources & Treatment
Links to other sites
U.S. Environmental Protection Agency
Washington State Department of Health, Division of Drinking Water
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