Fact Sheet - Drinking Water Glossary

6. Drinking Water Terms
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These definitions are not intended to be complete or to have legal force, but rather to help consumers quickly understand drinking water-related terms in the context of their daily lives.

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

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.

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

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

Coliform: 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.

Compliance: The act of meeting all state and federal drinking water regulations.

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

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.

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.

Finished Water: Water that has been treated and is ready to be delivered to customers.

Giardia lamblia: A microorganism frequently found in rivers and lakes, which, if not treated properly, may cause diarrhea, fatigue, and cramps after ingestion.

Ground Water: The water that systems pump and treat from aquifers (natural reservoirs below the earth's surface).

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.

Maximum Contaminant Level (MCL): The highest level of a contaminant that should be allowed in drinking water. MCLs ensure that drinking water does not pose either a short-term or long-term health risk.

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.

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.

Monitoring: Testing that water systems must perform to detect and measure contaminants.

Non-Transient, Non-Community Water System: A water system which supplies water to 25 or more of the same people at least six months per year in places other than their residences. Some examples are schools, factories, office buildings, and hospitals which have their own water systems.

Organic Contaminants: Carbon-based chemicals, such as solvents and pesticides, which can get into water through runoff from cropland or discharge from factories.

Pathogen: A disease-causing organism.

Public Notification: An advisory that a water system may distribute to affected consumers when the system has violated MCLs or other regulations. The notice advises consumers what precautions, if any, they should take to protect their health.

Public Water System (PWS): Typically, any water system which provides water to at least 25 people for at least 60 days annually.

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.

Sample: The water that is analyzed for the presence drinking water contaminants. Agencies may take samples from source water, from water leaving the treatment facility, or from the taps of selected consumers.

Sanitary Survey: An on-site review of the water sources, facilities, equipment, operation, and maintenance of a public water systems for the purpose of evaluating the adequacy of the facilities for producing and distributing safe drinking water.

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

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

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

Transient, Non-Community Water System: A water system which provides water in a place such as a gas station or campground where people do not remain for long periods of time. These systems do not have to test or treat their water for contaminants which pose long-term health risks because fewer than 25 people drink the water over a long period. They still must test their water for microbes and several chemicals.

Treatment Technique: 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.

Violation: A failure to meet any state or federal drinking water regulation.

Vulnerability Assessment: An evaluation of drinking water source quality and its vulnerability to contamination by pathogens and toxic chemicals.

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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Adapted From:
EPA 815-K-97-002
Water On Tap
July 1997

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