An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Monitoring Unregulated Drinking Water Contaminants

Learn About the Unregulated Contaminant Monitoring Rule

EPA uses the Unregulated Contaminant Monitoring Rule (UCMR) to collect data for contaminants that are suspected to be present in drinking water and do not have health-based standards set under the Safe Drinking Water Act (SDWA).

On this page:

Why was the UCMR program developed?

The SDWA Amendments of 1996 provide for:

  • Monitoring no more than 30 contaminants every five years
  • Monitoring large systems and a representative sample of small public water systems serving less than or equal to 10,000 people
  • Storing analytical results in a National Contaminant Occurrence Database (NCOD)

Occurrence data are collected through UCMR to support the Administrator's determination of whether to regulate particular contaminants in the interest of protecting public health.

EPA’s selection of contaminants for a particular UCMR cycle is largely based on a review of the Contaminant Candidate List (CCL). The UCMR program was developed in coordination with the CCL.

The CCL is a list of contaminants that:

  • Are not regulated by the National Primary Drinking Water Regulations
  • Are known or anticipated to occur at public water systems
  • May warrant regulation under the SDWA

EPA pays for the analysis of all samples from systems serving 10,000 or fewer people. EPA coordinates an approval program for laboratories that wish to analyze public water system samples.

Top of Page

How does EPA select the contaminants for UCMR?

EPA reviews contaminants that have been evaluated through existing prioritization processes, including previous UCMR contaminants and the CCL. Additional contaminants may be identified based on current research on occurrence and health effect risk factors.

Chemicals that are not registered for use in the United States, do not have an analytical reference standard, or do not have an analytical method ready for use are generally removed from consideration.

EPA further prioritizes remaining contaminants based on more extensive health effects evaluations, typically performed by the Office of Water’s Office of Science and Technology. The procedures for evaluating health effects were developed to support the ranking of contaminants for future CCLs.

Top of Page

What are the public health benefits of UCMR?

UCMR provides EPA and others with scientifically valid data on the occurrence of these contaminants in drinking water. This permits 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.

Top of Page