UCMR 6: EPA sidesteps microplastics, for now

Crowell | July 9, 2026

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"Summary

On July 1, 2026, EPA proposed the sixth Unregulated Contaminant Monitoring Rule (UCMR 6), which will require public water systems (PWS) to monitor 30 unregulated contaminants — including certain PFAS chemicals — but not microplastics. For now, EPA is using other tools, such as the Contaminant Candidate List (CCL), to learn more about microplastics before requiring PWSs to monitor for them.

UCMR 6

What UCMR 6 Would Require

Under the Safe Drinking Water Act (SDWA), Congress established a multi-step, risk-based approach for determining which contaminants would become subject to drinking water standards. Step one is the CCL, a list of contaminants not subject to any proposed or promulgated drinking water standards, that are known or anticipated to occur in PWS and may require future action under SDWA. Step two is the UCMR program, which mandates monitoring every five years of a subset of unregulated contaminants on the CCL to determine their frequency and level of occurrence in drinking water systems. Step three is the regulatory determination process, where the U.S. Environmental Protection Agency (EPA) must determine every five years whether to regulate at least five contaminants from the CCL.

The proposed UCMR 6 rule (the sixth to be issued under the program) covers 30 contaminants drawn from the CCL that are organized in four groups: (1) seven ultrashort organofluorine compounds, (2) three pesticide metabolites, (3) 13 semivolatile organic compounds, and (4) seven purgeable organic compounds. The seven ultrashort organofluorine compounds include four per- and polyfluoroalkyl substance (PFAS) compounds (PFMOAA, PFPrA, PFPrS, and PFEtS) that have been less thoroughly studied than more commonly known PFAS compounds (such as PFOA and PFOS) but are a concern due to their increased global production and use. EPA now has a testing method, identified in the UCMR 6 proposal, that PWS can use to determine their occurrence in drinking water. EPA will utilize the data collected under UCMR 6 to determine whether to regulate any of the listed contaminants through a separate regulatory determinations process."