Unregulated Contaminant Monitoring Rule FAQs

The EPA currently has drinking water regulations for more than 90 contaminants.  The 1996 Safe Drinking Water Act (SDWA) amendments require that once every five years the EPA issue a new list of no more than 30 unregulated contaminants to be monitored by public water systems. The UCMR program was developed in response to the 1996 amendment in coordination with the Contaminant Candidate List (CCL). The CCL is a list of contaminants that are not regulated by the National Primary Drinking Water Regulations, but are known or anticipated to occur in public water systems.

The first Unregulated Contaminant Monitoring Rule (UCMR1) was published on September 17, 1999, the second (UCMR2) was published on January 4, 2007, the third (UCMR3) was published on May 2, 2012, the fourth (UCMR4) was published on December 20, 2016, and the fifth (UCMR5) was published on December 27, 2021. This monitoring provides a basis for future regulatory actions to protect public health. While the EPA requires utilities to report results in their annual Water Quality Reports (also known as Consumer Confidence Reports), a Maryland law (effective October 1, 2013) requires WSSC Water to report detected contaminants within 30 days of receiving test results.

EPA reviewed contaminants that had been targeted through existing prioritization processes, including previous UCMR contaminants and the Contaminant Candidate List (CCL). Additional contaminants were identified based on current research on occurrence and health effect risk factors. Pesticides that were not registered for use in the United States, contaminants that did not have an analytical reference standard and contaminants whose analytical methods were not ready for use were removed from the list. EPA further prioritized the remaining contaminants based on more extensive health effects evaluations by the Office of Water’s Office of Science and Technology. These procedures for evaluating health effects were developed to support the ranking of contaminants for future CCLs.

Contaminant monitoring is part of a larger process that EPA, states, tribes, water systems, and other partners use to protect drinking water. Health information is necessary to know whether these contaminants pose a health risk, but it is often incomplete for unregulated contaminants. Some contaminants may be harmful at low levels; others may be harmful only at much higher levels. UCMR examines what is in the drinking water, but additional health information is needed to know whether these contaminants pose a health risk.

UCMR benefits the environment and public health by providing EPA and other interested parties with scientifically valid data on the occurrence of these contaminants in drinking water, permitting assessment of the population being exposed and the levels of exposure. This data set is one of the primary sources of occurrence and exposure information the Agency uses to develop regulatory decisions for emerging contaminants.

If a Public Water System (PWS) monitoring for UCMR finds contaminants in its drinking water, it provides the information to its customers in an annual water quality report (also referred to as the Consumer Confidence Report) available online. This includes both regulated and unregulated contaminants. Most systems mail these reports directly to customers, and many reports are available from EPA’s  website (WSSC Water's annual reports are available here). EPA also makes the results available online via its National Drinking Water Contaminant Occurrence Database.  These results will be posted on an ongoing basis after they have been reviewed for quality.

For general information on UCMR, go to: https://www.epa.gov/dwucmr/fifth-unregulated-contaminant-monitoring-rule or contact the Safe Drinking Water Hotline at (800) 426-4791 or at: water.epa.gov/drink/contact.cfm. Another source for more specific information (including FAQs for specific contaminants included in UCMR) can be found at: https://drinktap.org/Water-Info/Whats-in-My-Water.