On October 29, 2026, H.R. 10947 (the Monitor Microplastics Now Act) was introduced in the U.S. House of Representatives. If enacted, the bill would require the U.S. Environmental Protection Agency (EPA) to include nanoplastics and microplastics in the Sixth Unregulated Contaminant Monitoring Rule (UCMR 6) under the Safe Drinking Water Act (SDWA) and would provide that their inclusion does not count toward the statutory limit of 30 unregulated contaminants. If EPA promulgates a final rule for UCMR 6 before the bill’s enactment, the bill would require EPA to reissue the final rule with nanoplastics and microplastics included. The bill defines “nanoplastic” as “a plastic fragment or particle less than 1,000 nanometers in diameter” and “microplastic” as “a plastic fragment or particle less than 5 millimeters in diameter.”

As previously explained, EPA declined to add microplastics to UCMR 6 when it released the proposed rule on July 1, 2026 (91 Fed. Reg. 39952), despite two petitions urging their inclusion. One was a November 26, 2025 petition from the Governors of New Jersey, Delaware, Illinois, Maryland, Michigan, Wisconsin, and Connecticut, submitted under SDWA section 1445(a)(2)(B)(ii), which requires EPA to include a contaminant recommended by seven or more governors unless doing so would prevent the listing of other contaminants of a higher public health concern. EPA concluded that there is currently no validated EPA or consensus drinking water analytical method for microplastics with the quality control, accuracy, and precision needed for UCMR 6, and that developing one within the statutory timeframe is not feasible. EPA said it will continue evaluating existing procedures and techniques (ASTM D8332-20 and D8333-20) to develop validated methods and adequate laboratory capacity to support national monitoring in a future UCMR. The bill would exempt nanoplastics and microplastics from the 30-contaminant limit, but EPA’s feasibility concerns would remain.

Comments on the proposed rule, including on EPA’s decision not to include microplastics, were due August 31, 2026. EPA is expected to finalize UCMR 6 around December 27, 2026.

In place of UCMR 6 inclusion, EPA is treating its April 2026 addition of microplastics as a group on the draft Sixth Contaminant Candidate List (CCL 6) as a first step toward defining and better understanding the potential public health risks of exposure through drinking water. As we discussed when CCL 6 was announced, that listing would channel greater federal focus and resources toward understanding the potential health impacts of microplastics in drinking water and could serve as a predicate to eventual regulation, though any such regulation is unlikely to come soon, and is unlikely before microplastics are monitored under a UCMR.

If the bill is enacted, EPA would have to add nanoplastics and microplastics to UCMR 6 notwithstanding its stated feasibility concerns. The bill does not address analytical methods or set a deadline for reissuing a final rule, which leaves open what method water systems would be required to use and when a reissued rule would take effect. Adding microplastics to UCMR 6, rather than to a later UCMR, could shorten the path to regulation, because SDWA requires EPA to consider UCMR occurrence data when it evaluates whether to regulate a contaminant. Regulation requires findings on adverse human health effects, occurrence in public water systems at a frequency and levels of public health concern, and a meaningful opportunity for health risk reduction. Earlier monitoring would accelerate development of the factual record needed to support those findings.