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What is UCMR 5? EPA's PFAS and lithium testing, explained

Updated · Written from EPA, NSF, CDC and maker documents, each linked at the end · How we decide what to say

Short answer

The Fifth Unregulated Contaminant Monitoring Rule (UCMR 5) is EPA's 2023 to 2025 national screening of 29 PFAS and lithium in public water systems. It shows what is in the water, but it is not a compliance test and a result above a limit is not by itself a violation.

The short version

UCMR means Unregulated Contaminant Monitoring Rule. Every five years, EPA requires public water systems to test for contaminants that are not yet regulated, so EPA can learn how common they are. UCMR 5 covers 29 PFAS and lithium, and the sampling ran from 2023 to 2025. The law behind it (the National Defense Authorization Act for Fiscal Year 2020) directed EPA to include all PFAS for which a drinking water method had been validated.

Who was tested

According to EPA’s documentation, systems serving 3,300 or more people were required to participate, along with a nationally representative random sample of 800 smaller systems. That is why our utility pages cover systems serving at least 3,300 people with a complete PFAS result set, plus any smaller system EPA lists.

How the testing was done

Labs used two EPA methods (Method 533 and Method 537.1) for the PFAS and Method 200.7 for lithium. EPA published the final dataset in August 2026, by water system and sampling point. Each compound has a minimum reporting level (MRL); EPA’s MRLs for the 29 PFAS range from 2 to 20 ppt, and only results at or above the MRL are reported to EPA. A missing result means “not found at or above the MRL”, not zero.

UCMR 5 results are not compliance results

Legal compliance with a drinking water standard is determined from a utility’s own regulatory monitoring, as a running annual average, reported to the state. UCMR 5 results are occurrence data collected for EPA’s national picture. We compare each system’s results to the 2024 PFAS levels as a screening aid and label that clearly on every page (how we compute it). EPA’s 2024 limits for PFOA and PFOS (4 ppt each) remain in force, with a compliance date of 2029 and a proposed extension to 2031; EPA has proposed to rescind the limits for PFHxS, PFNA, GenX and the hazard-index mixture. Check EPA’s PFAS page for the current status.

How to use it

  1. Find your utility (guide).
  2. Open its page and read the compound table: what was detected, and how high.
  3. If detections are close to or above the 4 ppt level for PFOA or PFOS, ask your utility what it plans to do and read about filters certified for PFAS.
  4. If you use a private well, UCMR 5 does not cover you; see test kits compared.

Related guides

Sources

Not medical or legal advice. This guide summarizes public documents so you can ask better questions of your utility, your health department or a certified lab. For health concerns, talk to a clinician; for compliance questions, to your state drinking water program. Pages on this site that name products may earn a commission, as disclosed on the affiliate disclosure page.