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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).

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Why was the UCMR program developed?

The SDWA Amendments of 1996 and the amendments by Section 2021 of America’s Water Infrastructure Act of 2018 (AWIA) provide for:

  • Establishing a program to monitor for priority unregulated contaminants in drinking water every five years
  • Monitoring all large systems serving greater than 10,000 people Monitoring all small public water systems serving between 3,300 and 10,000 people, and a representative sample of small public water systems serving fewer than 3,300 people; this expanded scope is conditioned on the availability of appropriations and sufficient laboratory capacity
  • 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.

The UCMR program was developed in coordination with the Contaminant Candidate List (CCL) 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.

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How does EPA select the contaminants for UCMR?

In establishing the proposed list of contaminants for UCMR, EPA evaluates unregulated contaminants in accordance with its statutory authorities.

EPA considers the CCL and other priority contaminants (e.g., those highlighted in the Agency’s PFAS Action Plan). Further, EPA considered the opportunity to use multi-contaminant methods to collect occurrence data in an efficient, cost-effective manner.

EPA evaluates candidate UCMR contaminants using a multi-step prioritization process. The first step includes identifying contaminants that: (1) were not monitored under prior UCMR cycles; (2) may occur in drinking water; and (3) are expected to have a completed, validated drinking water method in time for rule proposal.

The next step is to consider the following: availability of health assessments or other health-effects information (e.g., critical health endpoints suggesting carcinogenicity); public interest (e.g., PFAS); active use (e.g., pesticides that are registered for use); and availability of occurrence data.

During the final step, EPA considers stakeholder input; looks at cost-effectiveness of the potential monitoring approaches; considers implementation factors (e.g., laboratory capacity); and further evaluates health effects, occurrence, and persistence/mobility data to identify the list of proposed UCMR contaminants..

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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.

UCMR data represent one of the primary sources of national occurrence data in drinking water that EPA uses to inform regulatory and other risk management decisions for drinking water contaminant candidates.

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