Under the 1996 amendments to the federal Safe Drinking Water Act, the U.S. Environmental Protection Agency is required once every five years to issue a new list of up to 30 unregulated contaminants for which public water systems must monitor. The intent of this rule is to provide baseline occurrence data that the EPA can combine with toxicological research to make decisions about potential future drinking water regulations.
The most recent UCMR, the Fourth Unregulated Contaminant Monitoring Rule
(UCMR4), was signed by former EPA Administrator Gina McCarthy on Dec. 20, 2016. The EPA, the states, laboratories and public water systems participate in the testing for UCMR4 in various ways. The testing occurs between January 2018 and December 2020.