Water Quality Standards

A public water system (PWS) is a system for the provision to the public of water for human consumption through pipes or other constructed conveyances, if such system has at least fifteen service connections or regularly serves at least twenty-five individuals.

The public drinking water systems regulated by EPA, and delegated states and tribes, provide drinking water to 90 percent of Americans. These public drinking water systems, which may be publicly- or privately-owned, serve at least 15 service connections or 25 persons. Private, individual household wells, are not regulated by EPA.

Federal Water Quality Standard Regulations

The Water Quality Standards Regulation (40 CFR 131) establishes the requirements for states and tribes to review, revise, and adopt water quality standards. It also establishes the procedures for EPA to review, approve, disapprove, and promulgate water quality standards pursuant to section 303 (c) of the Clean Water Act.

National Primary Drinking Water Regulations

National Primary Drinking Water Regulations (NPDWRs or primary standards) are legally enforceable standards that apply to public water systems. Primary standards protect public health by limiting the levels of contaminants in drinking water.

List of Contaminants & their MCLs

An alphabetical listing with links to fact sheets on the primary drinking water regulations.



Disinfection Byproducts

Inorganic Chemicals

Organic Chemicals


Massachusetts Department of Environmental Protection (DEP)

Water Supply Webpage

Any questions, comments or concerns call the Water Quality Laboratory at 617-349-4780 any time, if no answer leave a message or email us.