UCMR 6: EPA Sidesteps Microplastics, For Now

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.

EPA Declined to Include Microplastics

As we reported in our May 2026 client alert, this spring, EPA placed microplastics on its draft CCL 6 as a first step toward defining and better understanding potential public health risks from exposure via drinking water. At that time, EPA was being pressured by several parties — including 15 attorneys general, seven governors, and more than 170 organizations — to also include microplastics on its draft UCMR 6.

EPA declined to include microplastics in the UCMR 6 proposal because the agency stated there is no consensus drinking water analytical method for PWS to use to successfully monitor for microplastics.

But the agency did not close the door on monitoring microplastics in the future. EPA plans to collaborate with other federal agencies to evaluate risks and exposures of microplastics to enable future monitoring for those microplastics that present potential health risks. This approach will also enable the EPA “to list microplastics on a future UCMR” when national monitoring is scientifically feasible through the availability of a validated drinking water analytical method.

Industry Takeaways

Companies operating in the water and chemical sectors should take note of the following:

• No Near-Term Microplastics Monitoring Mandate, but EPA Will Continue to Investigate Microplastics. EPA’s exclusion of microplastics from UCMR 6 means that drinking water systems will not be required to monitor for microplastics under this rule cycle, which runs through 2030. But EPA has not closed the door on including microplastics in a future UCMR. For now, the agency is learning more about microplastics via its listing of the contaminants on the draft CCL 6.
• Regulatory Risk Remains. Although EPA is moving cautiously, the breadth and political diversity of stakeholders pushing for microplastics regulation — including environmental advocates, state attorneys general, and governors — signals sustained pressure on EPA that could accelerate future rulemaking. As we have mentioned in prior alerts, several states have recently introduced bills or regulations targeting microplastics in drinking water, consumer products, and washing machines. Companies should monitor state-level developments closely, as state obligations may emerge independent of any federal action.
• Litigation Risk. EPA’s continued focus on microplastics — and its acknowledgement that it could list microplastics in a future UCMR — will continue to draw attention from the plaintiffs’ bar. Plaintiffs’ lawyers could use EPA’s statements in the draft and final UCMR 6, and the developing administrative record, to support foreseeability and causation claims in tort and public nuisance litigation against relevant companies. Given EPA’s interest, companies that manufacture, use, or release microplastics should continue to evaluate and assess their potential litigation risks.
• PFAS Compliance Remains Active. The proposed UCMR 6 will require PWS to collect occurrence data on additional PFAS chemicals, which could lead to new regulations for these chemicals in the future. Historical UCMR data on PFAS compounds has directly informed EPA's subsequent regulatory determinations for those substances, including the 2024 National Primary Drinking Water Regulation for PFOA and PFOS. The UCMR 6 occurrence data for this new cohort of compounds is therefore likely to serve as the evidentiary foundation for future regulatory action. Companies should continue to monitor PFAS developments closely.

EPA will host two webinars, on August 11 and 12, 2026, respectively, to discuss the proposed monitoring requirements, contaminant selection and rationale, drinking water analytical methods, and the laboratory approval process. Comments on the proposed UCMR 6 must be received on or before August 31, 2026.

Crowell & Moring has been closely monitoring updates to microplastics rules and legislation on both the federal and state levels, and we will continue to provide updates as this area of law develops.