The U.S. EPA proposed the Sixth Unregulated Contaminant Monitoring Rule, UCMR 6, on July 1, 2026. Under the Safe Drinking Water Act, EPA must issue a list of unregulated contaminants for monitoring once every five years, and UCMR 6 would require public water systems to sample for 30 chemical contaminants between 2028 and 2030. For a small system operator the two questions that matter are simple: would my system be included, and what do I have to do about it now. This article is compliance information, not legal advice. The rule is proposed, not final, and the details below track the proposal as published.

What UCMR is and why it exists

UCMR monitoring is data collection, not a violation check. The contaminants on the list are unregulated, meaning there is no enforceable drinking water standard for them yet. EPA uses the monitoring results to decide which contaminants may need future regulation. It is the same program that produced the national occurrence data behind the 2024 PFAS rule. Participating systems do not fail UCMR sampling the way they fail an MCL test, but the sampling obligation itself is mandatory for the systems the rule covers, and missed samples become reporting violations on the SDWIS record.

See exactly what your system is up against

Search by system name or PWSID and get your EPA violation history, open requirements, and upcoming deadlines in under a minute. Free, no account, no obligation.

Which systems would be included

As proposed, UCMR 6 covers community water systems (CWS) and non-transient non-community water systems (NTNCWS):

  • All systems serving more than 10,000 people.
  • All systems serving 3,300 to 10,000 people. Participation here is subject to the availability of annual appropriations and sufficient laboratory capacity.
  • A representative sample of 800 systems serving fewer than 3,300 people, selected by source type, also subject to appropriations and laboratory capacity.

The practical read for small systems: if you serve 3,300 or more, expect to be included once the rule is final. If you serve fewer than 3,300, you may be randomly selected, and EPA pays the analytical cost either way. Under the proposal, EPA covers all analytical costs for systems serving 10,000 or fewer people; large systems pay their own laboratory costs.

The 30 contaminants and what they signal

The proposed list is a snapshot of what EPA is watching next. Three groups stand out.

Ultrashort organofluorine compounds. Eight of the 30 are short-chain PFAS-family compounds including trifluoroacetic acid (TFA), trifluoromethanesulfonic acid (TFMS), perfluoropropanoic acid (PFPrA), PFMOAA, and related perfluorosulfonic acids. These are the breakdown products and industrial intermediates that have been turning up in water supplies as the older long-chain PFAS are phased out. They are distinct from the four MCL compounds in the 2024 PFAS rule, and occurrence data from UCMR 6 would be the basis for any future standard.

Pesticides and metabolites. The list includes chlorothalonil, DEET, metribuzin, phorate (plus its sulfoxide and sulfone metabolites), trifluralin, dichlorvos, and 1,3-dichloropropene. Several are evaluated at parts-per-trillion-level reporting limits, far below anything a routine pesticide scan would catch.

Solvents and industrial intermediates. The group includes 1,2,3-trichloropropane (1,2,3-TCP), 1,1,1,2- and 1,1,2,2-tetrachloroethane, hexachlorobutadiene, naphthalene, and 2,4- and 2,6-dinitrotoluene. These are the classic dry-cleaning and industrial solvents that show up near contaminated groundwater.

Samples would be taken at the entry point to the distribution system using four EPA analytical methods: 524.3 with enhanced sensitivity, 525.3, 540, and 563.

The timeline

The proposal was published in the Federal Register on July 1, 2026, and EPA held public webinars on August 11 and 12, 2026. A final rule has not been issued. As proposed, sampling would occur during a 12 month period within January 2028 through December 2030, with large systems first and small systems phased in as EPA finalizes its sampling design for each collection year. Until the final rule publishes, no system is required to sample under UCMR 6, and no system should pay a lab to run these methods yet.

What a small system should do now

First, confirm your system classification and population. Whether you are a CWS or NTNCWS, and whether your population is above or below 3,300, decides whether inclusion is certain or random. Second, do not confuse UCMR 6 with the PFAS rule: the April 2024 PFAS MCLs are enforceable today, while UCMR 6 is future data collection. Systems that have not completed PFAS initial monitoring owe that obligation regardless of UCMR 6. Third, when the final rule publishes, the systems selected will be notified through their primacy agency, and the practical burden is scheduling: coordinating with an approved laboratory, sampling at the entry point, and reporting results through the state.

The UCMR 6 story is the same story as every other monitoring obligation: the systems that get caught are the ones that did not know they were in the cycle. A system specific compliance record tells you which rules already apply to you today, so when the next rule lands, it is a schedule change, not a surprise.

Get Your Compliance Roadmap — $199 at orevant.com. See what your system already owes free first: check your water system's record free.

FAQ

Does my small water system have to sample under UCMR 6?

If you serve more than 3,300 people and the rule is finalized as proposed, yes. Systems under 3,300 are sampled only if randomly selected from the 800-system representative sample, subject to appropriations and laboratory capacity.

Is UCMR 6 in effect now?

No. It was proposed July 1, 2026. No system is required to sample until a final rule is published and its sampling period begins.

Who pays for UCMR 6 sampling?

As proposed, EPA pays all analytical costs for systems serving 10,000 or fewer people. Systems serving more than 10,000 pay their own costs.

Are the UCMR 6 PFAS compounds regulated?

No. They are unregulated contaminants under study. The enforceable PFAS MCLs from the April 2024 rule apply to PFOA, PFOS, PFHxS, PFNA, and HFPO-DA, not to the ultrashort compounds on the UCMR 6 list.

Sources: EPA, Proposed Sixth Unregulated Contaminant Monitoring Rule (EPA-HQ-OW-2023-0469); Federal Register, Vol. 91, July 1, 2026, 2026-13263; Safe Drinking Water Act 42 U.S.C. §300j-4. Orevant provides compliance information tooling, not legal advice.