Action Level – The concentration of a contaminant, which, if exceeded, triggers treatment or other requirements that a water system must follow.

Maximum Contaminant Level – The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to the MCLGs as feasible using the best available treatment technology.

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

Inorganic Contaminants – Salts and metals, which can be naturally-occurring or result from urban storm water runoff, industrial or domestic discharges, oil and gas production, mining or farming.

Organic Chemical Contaminants – Synthetic and volatile organic chemicals that are byproducts of industrial processes and petroleum production. Organic chemical contaminants can also come from gas stations, urban storm water runoff and septic systems.

Radioactive Contaminants – Can be naturally occurring or the result of oil and gas production and mining activities.

Microbial Contaminants – Viruses and bacteria that come from sewage treatment plants, septic systems, agricultural livestock operations and wildlife.

Pesticides and Herbicides – Come from a variety of sources such as agriculture, urban storm water runoff and residential uses.

MCLGs allow for a margin of safety.

Nephelometric Turbidity Units – A measure of water clarity. Generally stated as NTU.

Picoruries Per Liter – A measure of radioactivity. Generally stated as pCi/l.

PPB – Stands for parts per billion or micrograms per Liter (up/L). One part per billion equals about one second in 32 years or one inch in 16,000 miles.

Treatment Technique – A required process intended to reduce the level of a contaminant in drinking water.

Maximum Residual Disinfectant Level – The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.

Maximum Residual Disinfectant Level Goal – The level of drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contamination.