EPA’s proposed Sixth Unregulated Contaminant Monitoring Rule (UCMR 6) would, if finalized as drafted, require community water systems nationwide to test for microplastics for the first time. The agency submitted the proposal to the White House Office of Management and Budget on March 27, 2026, with final rule publication expected later in 2026 and monitoring tentatively scheduled for 2027-2029. The resulting dataset would be the first federal occurrence record for microplastics in US drinking water.
What UCMR 6 Proposes
The UCMR program operates under Safe Drinking Water Act Section 1445(a)(2), which directs EPA to require monitoring for up to 30 unregulated contaminants every five years. The data is collected, reviewed, and used to inform future regulatory decisions — it does not itself set any enforceable limit.
The prior cycle, UCMR 5 (2023-2025), required community water systems to test for 29 PFAS compounds plus lithium using EPA methods 533 and 537.1. Results from that program, detailed in our UCMR 5 PFAS monitoring results coverage, have already influenced federal PFAS rulemaking.
UCMR 6, based on the proposal submitted to OMB, is expected to include:
- Microplastics — likely reported by polymer class, count, or mass depending on method availability
- Expanded PFAS coverage beyond the UCMR 5 list
- Selected pharmaceutical metabolites
- Certain pesticides and pesticide degradates
The rule would cover all community water systems serving more than 10,000 people on a mandatory basis, plus a nationally representative sample of smaller systems (typically those serving 3,300-10,000 people). Results are published through EPA’s National Contaminant Occurrence Database (NCOD), which is queryable at the utility level. That data feeds into Contaminant Candidate List (CCL) updates and eventual regulatory determinations — the pipeline described in our EPA CCL 6 microplastics news coverage.
Inclusion of microplastics follows a November 2025 petition from governors of seven states, which under SDWA Section 1445 obligates EPA to consider adding a contaminant to the UCMR unless doing so would displace higher-priority candidates.
Why Microplastics Are Difficult to Monitor
No EPA-approved analytical method for microplastics in drinking water exists as of April 2026. That gap is the single largest technical obstacle to nationwide monitoring.
California’s State Water Resources Control Board approved the first standardized methods in May 2022 — two standard operating procedures for particle extraction and measurement, one using infrared (IR) spectroscopy and one using Raman spectroscopy. Both were validated through a 22-laboratory interlaboratory study. Other research groups use pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) to measure microplastics by mass, which is a fundamentally different output than the particle counts produced by spectroscopic methods.
The counts-versus-mass divide matters. A utility reporting “particles per liter” and one reporting “micrograms per liter” are measuring related but non-interchangeable quantities. Inter-method harmonization is a prerequisite for nationwide data that can be meaningfully compared across systems.
Nanoplastics — particles smaller than one micron — are harder still. A 2024 study in the Proceedings of the National Academy of Sciences by Columbia and Rutgers researchers used stimulated Raman scattering microscopy to count roughly 240,000 particles per liter in bottled water, an order of magnitude higher than earlier estimates that measured only larger microplastics. Whether UCMR 6 would require nanoplastic detection, or limit scope to a specific size range (for example 1-500 microns), remains to be seen in the final rule text.
EPA has been coordinating with the Water Research Foundation and outside labs on method development and harmonization, though a federally approved method has not been published.
What This Means for Your Tap Water
If UCMR 6 is finalized with microplastics included, and your utility serves more than 10,000 people, your water supplier would be required to monitor for and publicly report microplastic concentrations during the 2027-2029 testing window. For a sampled subset of smaller systems, the same requirement would apply.
Monitoring alone does not trigger any treatment requirement. No Maximum Contaminant Level (MCL) would be set on the basis of UCMR results by themselves. Detection data flows into NCOD, becomes searchable by utility, and informs a later regulatory determination — a multi-year process that has historically taken a decade or more, as documented in our microplastics contaminant profile.
State-level action is moving faster. California’s monitoring program is already underway, and several other states are considering similar frameworks. If you live in California, monitoring data at the source-water level is being collected now, separate from any federal timeline.
Who’s Affected and When
The UCMR framework covers a defined universe of systems:
- Community water systems serving more than 10,000 people — approximately 4,500 systems nationally, mandatory monitoring
- A representative sample of systems serving 3,300-10,000 people — approximately 800 systems, mandatory
- A subset of very small systems (under 3,300 people) — voluntary or state-selected in some cycles
Roughly 80% of Americans receive water from utilities that would be in scope for UCMR 6 monitoring if the rule is finalized as proposed.
The timeline, as it stands in April 2026:
- March 27, 2026 — proposed rule submitted to OMB for review
- Mid-to-late 2026 — publication in the Federal Register, public comment period
- Late 2026 or 2027 — final rule
- 2027-2029 — monitoring window
- 2028-2030 — data publication to NCOD on a rolling basis
Utilities face real costs before any sample is collected. Method validation, lab certification, and sample handling protocols for microplastics do not yet exist at the federal level. Private well owners are not covered under UCMR at all.
What the Rollback Environment Means for UCMR 6
The same EPA that is advancing UCMR 6 is simultaneously pursuing a PFAS regulation rollback that would weaken parts of the 2024 PFAS drinking water rule. That is not a contradiction — monitoring and regulation are separate steps under SDWA.
Monitoring rules have historically attracted bipartisan support. Industry groups generally prefer data collection to regulation, since UCMR produces information without imposing treatment obligations. That political dynamic has helped previous UCMR cycles move forward under administrations with very different regulatory postures.
Two risks are worth tracking. First, the final rule could narrow the microplastics scope — for example by limiting monitoring to a single polymer class, or by deferring microplastics to UCMR 7 pending method development. Second, the timeline could slip. OMB review, public comment, and final rule issuance have each been extended in prior cycles. Whether microplastics survive to the final rule intact is the key open question.
What You Can Do
Check whether your utility serves more than 10,000 people. If it does, plan for monitoring data to begin appearing in 2028 or later. If it is smaller, monitoring coverage depends on whether your system is selected for the representative sample.
Do not wait for federal data before taking action at the tap. Certified point-of-use filters can reduce microplastic particles now. Reverse osmosis is the most effective approach for a broad particle size range — see our best reverse osmosis systems guide. For a lower-cost alternative, look at carbon-block best under-sink water filters or best water filter pitchers certified to relevant NSF standards.
When the proposed rule is published for public comment, submit comments — particularly if you are a utility, a state regulator, or a researcher with method-validation data to share.
How WaterVerge Tracks This
WaterVerge integrates UCMR data at the utility level as soon as it is published to NCOD. UCMR 5 PFAS results are already incorporated into city and utility pages. When UCMR 6 data begins publishing in 2028-2030, microplastic detections will appear on the same utility pages with the same sourcing, alongside PFAS, lead, and regulated-contaminant violation histories. Search your city to see what is already on file.