What is the Unregulated Contaminant Monitoring Rule?

The 1996 amendments to the Safe Drinking Water Act (SDWA) require that once every five years, the USEPA issue a list of no more than 30 unregulated contaminants to be monitored by public water systems (PWSs). The Unregulated Contaminant Monitoring Rule (UCMR) provides EPA and other interested parties with scientifically valid data on the occurrence of contaminants in drinking water. This data serves as a primary source of occurrence and exposure information that the agency uses to develop regulatory decisions.

More information about the Unregulated Contaminant Monitoring Program is available at: www.epa.gov/dwucmr

What does this information mean to me?

Contaminant monitoring is part of a larger process that USEPA, 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. We are required to collect samples from the finished drinking water and report the substances detected along with the average and range of results.

Unregulated Contaminant Monitoring Rule 3 (UCMR3) Sampling Results

The following unregulated substances were detected during UCMR3 sampling in 2015:

* Laboratory Minimum Reporting Level (MRL) is the lowest concentration that can be detected by laboratory equipment.

Unregulated Contaminant Monitoring Rule 4 (UCMR4) Sampling Results

The following unregulated substances were detected during UCMR4 sampling in 2018 and 2019:

* Laboratory Minimum Reporting Level (MRL) is the lowest concentration that can be detected by laboratory equipment.

Additional information on UCRM4 sampling is available on the EPA’s website at the following location:
https://www.epa.gov/dwucmr/fact-sheets-about-fourth-unregulated-contaminant-monitoring-rule-ucmr-4

Unregulated Contaminant Monitoring Rule 5 (UCMR5) Sampling Results

The following unregulated substances were detected during UCMR5 sampling in 2024 and 2025:

* Laboratory Minimum Reporting Level (MRL) is the lowest concentration that can be detected by laboratory equipment.

Additional information on UCRM5 sampling is available on the EPA’s website at the following location:
https://www.epa.gov/system/files/documents/2023-08/ucmr5-data-summary_0.pdf