On July 1, 2026, the U.S. Environmental Protection Agency published a proposed rule establishing the sixth Unregulated Contaminant Monitoring Rule (UCMR 6). If finalized, the rule would require public water systems to monitor 30 unregulated contaminants, including certain per- and polyfluoroalkyl substances (PFAS), during a three-year sampling window running from 2028 through 2030. The proposal represents the next iteration of EPA's long-standing program to gather occurrence data on contaminants that are not yet subject to national primary drinking water regulations but may warrant future regulatory action.
The proposed rule would apply to all community water systems and non-transient non-community water systems serving 3,300 or more people, along with a representative sample of smaller systems selected by EPA. Covered utilities should begin evaluating laboratory capacity, sampling logistics, and internal data management now, as the compressed monitoring window and expanded analyte list will likely strain existing compliance resources. Systems that have already invested in PFAS testing under UCMR 5 may find some infrastructure transferable, but new analytes and updated methods may require additional vendor coordination.
Notably, EPA declined to include microplastics in UCMR 6, citing the absence of a validated analytical test method. That decision signals that future rulemakings may revisit emerging contaminants as laboratory methods mature, and industry stakeholders should anticipate continued expansion of the monitored analyte universe in subsequent UCMR cycles. Industrial dischargers, product manufacturers, and other upstream sources of contaminants of concern should also be aware that UCMR data frequently informs downstream regulatory action, including maximum contaminant level development, state-level standards, and cost-recovery litigation.
EPA is accepting public comments on the proposed rule through August 31, 2026. The next several weeks therefore represent a critical window for water systems, trade associations, industrial stakeholders, and technology providers to shape the final rule's scope, sampling design, approved methods, and compliance timelines. Comments addressing technical feasibility, laboratory availability, and small system burdens have historically influenced final UCMR provisions and remain the most direct means of engagement.
This update is provided for general informational purposes only and does not constitute legal advice. Clients facing UCMR 6 compliance questions or considering participation in the rulemaking should seek tailored counsel regarding their specific circumstances.