Drinking Water Standard in the United States

Drinking Water Standard in Environmental Law

Limits the amounts of particular contaminants in the public water supply system. The Environmental Protection Agency (EPA) is authorized by the Safe Drinking Water Act to set primary standards for 83 contaminants, most of which have been completed. The standards are stated in terms of maximum contaminant levels (MCLs).

There are two types of standards: the National Primary Drinking Water Regulations and the National Secondary Drinking Water Regulations. The primary regulations are designed to protect the health of the public; the secondary standards address aesthetics such as odor and appearance. Only the primary standards are enforceable, and drinking water standards apply only to public water supply systems. A public water system is one that provides piped water for human use to an average of at least 25 persons or connections to 15 locations.

In establishing the maximum contaminant levels, the EPA first sets goals at a level where no adverse health effects are known or anticipated to occur, allowing an ample margin of safety. For contaminants that do not cause cancer, the goals are based on a reference dose (determined through tests) and assume that an individual will drink two liters of water from the same source every day for seventy years. For carcinogens, the EPA sets the goal at zero.

The primary standards are set as close to the goals as feasible, taking into consideration the best technology and treatment techniques available. The EPA must use field conditions (as opposed to laboratory analysis) as the basis for its determinations, and cost of treatment must be taken into account. If the EPA decides it cannot determine the appropriate maximum contaminant level, it can require specific types of treatment.

Secondary standards are advisory only; states may use them in their own laws if they choose, but the EPA cannot enforce them. An example of a contaminant with a secondary standard is fluoride, which discolors teeth, mottling them or turning them brown. Because fluoride does not actually damage teeth, a primary standard was not necessary to protect the health of the public, so the EPA declined to issue one. This decision was unpopular in many communities.
Based on “Environment and the Law. A Dictionary”.