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. MCLGs are non-enforceable health goals.

(microorganisms) Tiny living organisms that can only be seen with the aid of a microscope. Some microbes can cause acute health problems when consumed (see pathogens).

Testing that water systems must perform to detect and measure contaminants. A water system that does not follow US EPA’s monitoring methodology or schedule is in violation, and may be subject to legal action.

Legally enforceable standards that apply to public water systems. These standards protect drinking water quality by limiting the levels of specific contaminants that can adversely affect public health and which are known or anticipated to occur in public water supplies.

A public 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…

Carbon-based chemicals, such as solvents and pesticides, which can get into water through runoff from cropland or discharge from factories. US EPA has set legal limits on 56 organic contaminants.

Disease-causing organisms, such as some bacteria, viruses, or protozoa.

Primary enforcement authority for the drinking water program. Under the Safe Drinking Water Act, states, U.S. territories, and Indian tribes that meet certain requirements, including setting regulations that are at least as stringent as US EPA’s, may apply for, and…

An advisory that US EPA or the state requires a water system to distribute to affected consumers when the system has violated Maximum Contaminant Levels or other regulations. The notice advises consumers what precautions, if any, they should take to…

Any water system which provides water to at least 15 service connections or 25 people for at least 60 days annually. There are more than 170,000 PWSs providing water from wells, rivers, and other sources to about 250 million Americans.…