The U.S. Environmental Protection Agency (EPA) has released its proposed Sixth Unregulated Contaminant Monitoring Rule (UCMR 6), launching the next nationwide effort to collect occurrence data on contaminants that are not currently regulated under the Safe Drinking Water Act (SDWA). The proposed UCMR 6 monitoring program would require public water systems across the United States to sample for 30 unregulated contaminants between 2028 and 2030, generating data that could influence future drinking water regulations and Maximum Contaminant Levels (MCLs). While drinking water regulations for PFAS are reducing the number of analytes required for compliance, UCMR 6 is expanding the PFAS monitoring scope.
Issued every 5 years, the UCMR program serves as EPA’s primary mechanism for identifying emerging drinking water contaminants and evaluating whether future regulatory action may be warranted.
Proposed UCMR 6 Contaminants and Monitoring Scope
Under the proposed rule, EPA would require monitoring for 30 unregulated chemical contaminants. While the agency expanded its focus on ultrashort-chain fluorinated compounds, including additional PFAS, several highly visible contaminant groups, including microplastics and pharmaceuticals, were not included because standardized analytical methods and sufficient laboratory validation are not yet available. EPA will continue to monitor the development of new methods for any future UCMR listing.
The proposed UCMR 6 contaminant list includes four major categories analyzed by specific laboratory methods:
- Ultrashort Organofluorine Compounds via EPA 563: seven compounds are included, with four of them classified as short-chain per- and polyfluoroalkyl substances (PFAS), as defined by the 5th Contaminant Candidate List.
- Pesticide Metabolites via EPA 540: three specific chemical degradation products are listed resulting from agricultural applications.
- Semivolatile Organic Compounds (SVOCs) via EPA 525.3: thirteen industrial chemical intermediates and compounds are included with limited national occurrence data.
- Purgeable Volatile Organic Compounds (VOCs) via EPA 524.3: comprise of seven industrial solvents and volatile organic agents.
These 30 proposed contaminants represent EPA’s target focus on highly mobile compounds that may persist in source waters. Gathering this national baseline is intended to fill critical data gaps regarding their occurrence and concentration levels, providing the necessary foundation for future regulatory determinations.
UCMR 6 Monitoring Requirements and Timeline
The EPA plans to finalize UCMR 6 in 2027, with monitoring occurring during a 12-month period for each participating utility between January 2028 and December 2030. The proposed monitoring framework closely follows previous UCMR cycles and applies to community water systems (CWSs) and non-transient non-community water systems (NTNCWSs).
| Year | Key Milestones |
| 2026 | EPA publishes the proposed UCMR 6 rule and opens the public comment period |
| 2027 | EPA is expected to finalize UCMR 6 and begin program implementation activities, including laboratory approvals and monitoring preparations. |
| 2028-2030 | Participating public water systems conduct monitoring, submit analytical results, and contribute occurrence data to EPA’s national database. |
| 2031 | EPA completes reporting and program activities and begins evaluating the monitoring data results to support future regulatory decisions. |
In addition to outlining key program milestones, the proposed rule establishes participation requirements and funding responsibilities based on public water system size, as shown in the table below.
| System Size (Population Served) | Participation Requirement | Cost Responsibility |
| Large Systems (>10,000 people) | All systems nationwide | Utility-funded |
| Mid-Sized Systems (3,300 to 10,000 people) | All systems nationwide | Covered by the EPA (subject to appropriations) |
| Small Systems (<3,300 people) | Representative sample of 800 randomly selected systems | Covered entirely by the EPA |
While monitoring requirements apply directly to participating public water systems, UCMR 6 may also affect organizations that support drinking water monitoring and compliance. These stakeholders include municipal, state, local, and tribal entities that operate water systems or conduct sampling and analysis on their behalf, as well as private operators of community and non-transient non-community water systems.
Operational Considerations for Water Utilities
For public water utilities, the transition from UCMR 5 to the proposed UCMR 6 framework introduces distinct logistical and operational requirements. Systems subject to the rule will need to coordinate with laboratory networks to manage:
- Laboratory Approval: Only facilities approved by EPA are allowed to analyze UCMR6 samples this is to ensure that the laboratories can meet the commensurate measurement and performance criteria.
- Sampling Logistics: Aligning sample collection windows at the entry points to the distribution system (EP) within the mandatory 12-month monitoring period.
- Data Reporting: Submitting analytical results through the web-based Safe Drinking Water Accession and Review System (SDWARS 6) within the designated compliance windows.
- Public Information Integrity: Preparing consumer confidence reports (CCRs) as required by the SDWA if unregulated contaminants are detected at or above the minimum reporting levels (MRLs).
Why UCMR 6 Matters for Future Drinking Water Regulations
The UCMR program does not establish new drinking water standards. Instead, it provides EPA with the nationwide occurrence data needed to evaluate potential health risks and determine whether future regulatory action is warranted.
Previous UCMR cycles helped inform regulatory decisions related to PFAS and other emerging contaminants. The proposed UCMR 6 rule continues that process by focusing on unregulated chemicals with limited national occurrence data. For public water systems, environmental professionals, and drinking water stakeholders, the results could shape future compliance obligations, treatment planning, and emerging contaminant management strategies.
UCMR 6 Public Comment Period and Next Steps
The EPA has opened a 60-day public comment window for the draft rule, concluding on August 31, 2026. The agency will host two technical webinars on August 11 and 12, 2026, to discuss the rationale for contaminant selection, laboratory approval protocols, and analytical method sensitivity. Comments must be submitted to the federal regulatory docket under Docket ID No. EPA-HQ-OW-2023-0469.
