Action Level

The level of lead or copper which, if exceeded in over 10% of the homes tested, triggers treatment or other requirements that a water system must follow.

Acute Health Effect

An immediate (i.e., within hours or days) adverse health effect that may result from exposure to certain drinking water contaminants (e.g., pathogens).

Best Available Technology

The water treatment(s) that the US EPA certifies 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 Maximum Contaminant Level.

Community Water System

A public water system which supplies drinking water to 25 or more of the same people year-round in their residences.


The act of meeting all state and federal drinking water regulations


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


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 are likely to have more severe and more persistent symptoms than healthy individuals.


A chemical (commonly chlorine, chloramine, or ozone) or physical process (e.g., ultraviolet light) that kills microorganisms such as bacteria, viruses, and protozoa.

Disinfectant Byproducts

Disinfectant Byproducts are chemicals that may form when disinfectants (such as chlorine), react with plant matter and other naturally occurring materials in the water. These byproducts may pose health risks in drinking water.