On April 2, 2026, the EPA published its draft Sixth Contaminant Candidate List (CCL 6), marking the first time the agency has designated microplastics and pharmaceuticals as priority contaminant groups under the Safe Drinking Water Act. The announcement, made jointly by EPA Administrator Lee Zeldin and HHS Secretary Robert F. Kennedy Jr., also includes PFAS, disinfection byproducts, 75 individual chemicals, and nine microbes — the broadest CCL the agency has ever proposed.
The same day, HHS launched a $144 million research initiative called Systematic Targeting of MicroPlastics (STOMP) to measure microplastic accumulation in the human body and study its health effects. EPA simultaneously released human health benchmarks for 374 pharmaceuticals, giving states and local water systems a reference tool to assess risk when drug residues are detected.
What’s on the Draft CCL 6
The CCL is a watchlist — contaminants not yet regulated under federal drinking water standards but known or anticipated to occur in public water systems. Draft CCL 6 is the largest and most structurally ambitious list to date:
| Category | Count | Notable Inclusions |
|---|---|---|
| Chemical groups | 4 | Microplastics, pharmaceuticals, PFAS, disinfection byproducts |
| Individual chemicals | 75 | Various organic and inorganic contaminants |
| Microbes | 9 | Pathogens anticipated in public water systems |
The inclusion of contaminant groups rather than only individual chemicals represents a shift in the EPA’s approach. Previous CCLs listed specific compounds; CCL 6 acknowledges that categories like microplastics and pharmaceuticals encompass thousands of individual substances that share common exposure pathways.
What This Does — and Doesn’t — Do
Being placed on the CCL does not create any enforceable drinking water standard. It does not require water systems to test for these contaminants or treat their water differently. The CCL is the first step in a multi-stage regulatory pipeline:
- CCL listing — identifies contaminants for further study (where we are now)
- Monitoring — EPA may add contaminants to a future Unregulated Contaminant Monitoring Rule (UCMR) to collect nationwide occurrence data
- Regulatory determination — EPA evaluates whether a contaminant meets three statutory criteria for regulation
- Rulemaking — if a positive determination is made, EPA proposes and finalizes an MCL
That pipeline is slow. The CCL program has existed since 1996. In three decades, only one class of contaminants from the CCL has been regulated through to a final MCL: PFAS, which first appeared on CCL 1 in 1998 and received enforceable limits in April 2024 — a 26-year journey. EPA’s own CCL 5 regulatory determination, published just two weeks before CCL 6, declined to regulate all nine contaminants it evaluated, including microcystins and cylindrospermopsin.
For microplastics specifically, a major obstacle remains: there is no standardized EPA method for measuring microplastics in drinking water. Without an approved analytical method, the contaminant cannot be added to a UCMR, and without monitoring data, the agency cannot make a regulatory determination. Experts have noted that if microplastics miss inclusion in the next monitoring rule (UCMR 6), it could be another decade before systematic occurrence data becomes available.
Why Microplastics and Why Now
Research on microplastics in drinking water has accelerated sharply. Studies have detected plastic particles smaller than 5 millimeters in tap water, bottled water, and treated drinking water worldwide. A 2024 study in the Proceedings of the National Academy of Sciences found an average of 240,000 nanoplastic particles per liter of bottled water — orders of magnitude more than previously estimated when using methods that detect only larger particles.
The health effects of ingesting microplastics remain under active investigation, which is precisely what the HHS STOMP initiative aims to address. Early research has linked microplastic exposure to inflammation, oxidative stress, and potential endocrine disruption, but the EPA does not yet have sufficient data to establish a dose-response relationship for drinking water exposure.
The pharmaceutical component addresses a long-documented reality: medications enter the water supply through human excretion and improper disposal. Wastewater treatment plants are not designed to remove most pharmaceutical compounds, and trace levels of antibiotics, hormones, antidepressants, and other drugs have been detected in finished drinking water. The EPA’s new benchmarks for 374 pharmaceuticals give water systems their first federal reference point for evaluating these detections.
What You Can Do
-
Check your water now. Search your city on WaterVerge to review your water system’s current contaminant data, including PFAS detections from UCMR 5 monitoring and any disinfection byproduct violations.
-
Filter proactively. While microplastic and pharmaceutical MCLs are years away, filtration technology already addresses both. Reverse osmosis systems remove microplastics and most pharmaceutical compounds — see our guide to the best RO systems. Activated carbon filters, including quality pitcher filters and under-sink systems, reduce many pharmaceutical residues and larger microplastic particles.
-
Submit a public comment. The 60-day comment period closes June 5, 2026. Comments can be submitted through the Federal Register notice or at regulations.gov under docket EPA-HQ-OW-2024-0581.
-
Test your water independently. If you want data now rather than waiting for federal monitoring, a certified lab water test can detect many of the individual contaminants on CCL 6. Microplastic testing is available through specialized labs, though costs ($150–$400) remain higher than standard water panels.
What Comes Next
The draft CCL 6 is expected to be finalized by November 17, 2026, after the public comment period closes and EPA consults with its Science Advisory Board. From there, the question is whether microplastics and pharmaceuticals are added to the next UCMR cycle — a decision that will determine whether nationwide monitoring data exists to support future regulation.
For now, the CCL 6 announcement is a signal of regulatory intent, not regulatory action. It puts water systems, filtration manufacturers, and the public on notice that these contaminants are on the federal radar. Whether that radar leads to enforceable limits depends on the science, the politics, and the pace of a process that has historically moved in decades, not years.