New Maine Drinking Water Rule Addresses PFAS Standards

Overview of the New Standards

Effective December 1, 2025, the Maine Center for Disease Control and Prevention (CDC) revised its drinking water standards to adopt Biden-era U.S. Environmental Protection Agency National Primary Drinking Water Regulations for certain per- and polyfluoroalkyl substances (PFAS).

Notably, Maine’s rule expressly adopts the April 2024 version of the EPA regulation as issued, notwithstanding that EPA has since taken action to rescind the regulations and reconsider the regulatory determinations for all but PFOA and PFOS. This means Maine’s rule now enforces the earlier, more expansive set of PFAS standards that apply to a broader array of compounds than those now recognized under the updated Federal framework.

The new rule significantly expands PFAS monitoring and treatment obligations for public water supply systems statewide. Changes to the rule include:

• Mandatory PFAS testing and reporting for all community water systems, non-transient non-community systems, and bottled-water suppliers. Exceedances of the new Maximum Contaminant Levels (MCLs) require prompt corrective action.
• Projected compliance costs: Maine CDC estimates at least $50 million in one-time capital investments across affected systems (nominally eligible for Federal revolving-loan funding) and $1,000–$100,000 in annual operations and maintenance per public water system.

The following PFAS MCLs are now the enforceable standards for public water systems in Maine:

Compound	MCL
PFOA	4 ppt
PFOS	4 ppt
PFHxS	10 ppt
PFNA	10 ppt
HFPO-DA (“GenX”)	10 ppt
Mixture of two or more: PFNA, PFHxS, HFPO-DA, and PFBS	Hazard Index ≤ 1

Comparison with Maine’s Interim Standard

Maine previously applied an interim limit of 20 ppt for six PFAS compounds (PFOA, PFOS, PFHpA, PFNA, PFDA, and PFHxS) alone or in combination, meaning compliance was based on aggregate concentration rather than the level of any particular substance. See P.L. 2021, ch. 82. Under the original legislation requiring promulgation of this rule revision, the interim standard was designed to remain in place only until DHHS adopted a final PFAS MCL rule, and it was automatically repealed upon the new rule’s effective date (12/1/25). DHHS’s promulgation of this new rule marks a fundamental shift to compound-specific limits: a system now exceeds the standard if any single compound surpasses its MCL threshold, regardless of the total PFAS concentration.

Implications for Public Water Systems and Regulated Entities

Systems that previously satisfied Maine’s 20-ppt combined PFAS limit may now fall out of compliance under the new compound-specific standards, prompting expanded testing, reporting, and modifications to water treatment processes. With lower individual MCL thresholds and broader coverage, the number of systems requiring PFAS treatment upgrades is expected to rise substantially. The associated costs, already projected in the tens of millions statewide, will demand substantial financial and infrastructure planning, even with Federal loan programs available.

These challenges are further compounded by a very significant reduction in available Federal funding through the Clean Water and Drinking Water State Revolving Funds (SRFs), which will make it increasingly difficult for utilities and water districts, particularly those serving smaller communities, to finance required upgrades. As a result, utilities and water districts may face difficult trade-offs between rate adjustments, phased implementation, or seeking alternative funding sources to remain in compliance.

The rule may be found at 10-144 C.M.R. Ch. 231 (Adoption Filing No. 2025-232). Additional background on the adopted rule is available from the Maine Department of Health and Human Services (DHHS).

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This article was contributed by Preti Flaherty attorneys Kevin Osantowski and David Van Slyke, and paralegal Olivia Capasso.