Definitions You Need to Know


Action Level (AL)
The concentration of a contaminant which, if exceeded, triggers a treatment or other requirement which a water system must follow.

Department of Environmental Quality (DEQ)
State agency charged with creating and enforcing drinking water standards. Visit their web site at: http://www2.state.id.us/deq/.

Environmental Protection Agency (EPA)
Federal agency charged with creating and enforcing drinking water standards. Visit their web site at: http://www.epa.gov/.   

Inorganic Chemicals
Chemical substances of mineral origin, such as lead and copper.

Maximum Contaminant Level (MCL)
The highest level of a contaminant that is allowed in drinking water. MCL’s are set as close to the MCLG’s as feasible using the best available treatment technology.

Maximum Contaminant Level Goal (MCLG)
The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLG’s allow for a margin of safety.

Million fibers per liter (MFL)
Measure of the presence of asbestos fibers that are longer than 10 micrometers.

Millirems per year (mrem/yr)
Measure of radiation absorbed by the body.

Nephelometric Turbidity Unit (NTU)
Nephelometric turbidity unit is a measure of the clarity of water. Turbidity in excess of 5 NTU is just noticeable to the average person.

Non-Detects (ND)
Not detected in the water at the testing limits, i.e. laboratory analysis indicates that the constituent is not present.

Organic Chemicals
Naturally occurring or synthetic substances containing mainly carbon, hydrogen, nitrogen, and oxygen. This includes most pesticides and industrial chemicals.

Parts per million (ppm), or milligrams per liter (mg/l)
Indicates the amount of a contaminant found in a million parts of water. This corresponds to one penny in $10,000.

Parts per billion (ppb), or micrograms per liter (ug/l)
Indicates the amount of a contaminant found in a billion parts of water. This corresponds to one penny in $10,000,000.

Parts per trillion (ppt), or nanograms per liter (nanograms/l)
One part per trillion corresponds to one minute in 2,000,000 years, or a single penny in $10,000,000,000.

Parts per quadrillion (ppq), or picograms per liter (picograms/l)
One part per trillion corresponds to one minute in 2,000,000,000 years, or a single penny in $10,000,000,000,000.

Picocuries per liter (pCi/L)
Measure of radioactivity in water.

Treatment Technique (TT)
A treatment technique is a required process intended to reduce the level of a contaminant in drinking water.

Variances & Exemptions (V&E)
State or EPA permission not to meet an MCL or a treatment technique under certain conditions.