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WSSC Water is participating in the U.S. Environmental Protection Agency’s (EPA) fifth round of the Unregulated Contaminant Monitoring Rule (UCMR5).  The Safe Drinking Water Act (SDWA) requires the U.S. Environmental Protection Agency (EPA) to establish criteria for a program to monitor unregulated contaminants in drinking water and to identify contaminants to be monitored every five years. The UCMR dataset is one of the primary sources of information on occurrence and population exposure EPA uses to develop regulatory decisions for contaminants in the public drinking water supply.  Under UCMR5, 10,311 utilities nationwide will monitor unregulated contaminants for a year to help the EPA determine the occurrence of these contaminants in drinking water and whether or not they need to be regulated for protection of public health.  

More information on UCMR5 is available here.

As part of the UCMR5 program, WSSC Water is collecting samples quarterly throughout 2023. Samples will be collected at our finished water taps from both the Patuxent and Potomac water treatment plants.  UCMR5 requires WSSC Water to collect drinking water samples for 29 per- and polyfluoroalkyl substances (PFAS) and lithium.  This data will help to improve EPA’s understanding of the frequency that 29 PFAS (and lithium) are found in the nation’s drinking water systems, and at what levels.  The first set of data collected under UCMR 5 for 29 PFAS and lithium is currently available. This data release represents approximately 7% of the total results that EPA expects to receive until completion of data reporting in 2026.  

We are committed to protecting public health and will continue to monitor and support EPA’s research on these contaminants.

*Parts Per Billion (ppb) = Half of a teaspoon of water in an Olympic-sized swimming pool would be about one part per billion. Also, the equivalent of one minute in 2,000 years, or one penny in $10 million.

Review the latest WSSC Water UCMR5 Test Results


MCL – Maximum Contaminant Level –  “The maximum permissible level of a contaminant in water which is delivered to any user of a public water system."(EPA)
MCLG – Maximum Contaminant Level Goal – “The level of a contaminant in drinking water below which there is no known or expected risk to health.” (EPA)

Last Modified: October 11, 2023, 9:43 am EDT