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

Aquifer
A natural underground layer, often of sand or gravel, that contains water.

Coliform
A group of related bacteria whose presence in drinking water may indicate contamination by disease-causing microorganisms.

Community Water System (CWS)
A water system that supplies drinking water to 25 people or more year-round in their residences Contaminant Anything found in water (including microorganisms, radionuclides, chemicals, minerals, etc.) which may be harmful to human health.

Cryptosporidium
Microorganism found commonly in lakes and rivers which is highly resistant to disinfection.

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

Distribution System
A network of pipes leading from a treatment plant to customers’ plumbing systems.

Ground Water
Water that is pumped and treated from an aquifer.

Inorganic Contaminants
Mineral-based compounds such as metals, nitrates, and asbestos; naturally occurring in some water, but can also enter water through human activities.

Maximum Contaminant Level
The highest level of a contaminant that EPA allows in drinking water (legally enforceable standard).

Maximum Contaminant Level Goal
The level of a contaminant at which there would be no risk to human health (not a legally enforceable standard).

Microorganisms
Tiny living organisms that can be seen only under a microscope; some can cause acute health problems when consumed in drinking water.

Non-Transient Non-Community Water System
A non-community water system that serves the same people more than six months of the year, but not year-round.

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

Pathogen
Disease-causing organism.

Public Water System (PWS)
A water system which supplies drinking water to at least 25 people, at least 60 days each year.

Sensitive Subpopulation
People who may be more vulnerable to drinking water contamination, such as infants, children, some elderly, and people with severely compromised immune systems.

Septic System
Used to treat sanitary waste; can be a significant threat to water quality due to leaks or runoff.

Source Water
Water in its natural state, prior to any treatment for drinking (i.e., lakes, streams, ground water).

Surface Water
Water that is pumped and treated from sources open to the atmosphere, such as rivers, lakes, and reservoirs.

Transient Non-Community Water System
A non-community water system that serves the public but not the same individuals for more than six months.

Violation
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.

Well
A bored, drilled or driven shaft whose depth is greater than the largest surface dimension, a dug hole whose depth is greater than the largest surface dimension, an improved sinkhole, or a subsurface fluid distribution system.