One of the most strategically important features of U.S. PFAS regulation is that the Safe Drinking Water Act (SDWA) allows states to establish maximum contaminant levels (MCLs) that are more stringent than federal standards—and once established, these state MCLs cannot be weakened in response to federal rollbacks. Several states had established their own PFAS drinking water standards before the U.S. EPA finalized its national MCLs in April 2024, and those state standards continue to drive treatment requirements and create commercial demand for water filtration systems independently of federal regulatory changes.
Massachusetts: The Nation’s Most Comprehensive State PFAS MCL
Massachusetts was among the first states in the nation to establish enforceable PFAS MCLs, setting a combined maximum contaminant level of 20 parts per trillion (ppt) for the sum of six PFAS compounds: PFOS, PFOA, PFNA, PFHxS, PFDA, and PFUnDA. This “sum-of-six” approach—established in 2020 and enforced by the Massachusetts Department of Environmental Protection (MassDEP)—applies to all public water systems in the Commonwealth serving 25 or more people year-round. The standard is more stringent than the EU Drinking Water Directive’s 100 ng/L sum-of-20 approach in numerical terms, and is applied to a subset of compounds that includes two (PFDA and PFUnDA) not individually regulated by the federal NPDWR. Water systems that exceed the 20 ppt combined limit must provide public notification, identify a source, and implement a treatment solution.
Michigan: 8 ppt for PFOS and PFOA, Stricter on Short-Chains
Michigan established some of the nation’s most comprehensive compound-specific PFAS MCLs, covering seven compounds. Key standards include: PFOS at 8 ppt; PFOA at 8 ppt; PFNA at 6 ppt; PFHxS at 51 ppt; PFDA at 6 ppt; PFHpA at 8 ppt; and PFBS at 420 ppt. Michigan’s MCLs for PFOS and PFOA at 8 ppt are twice as stringent as the federal 4 ppt MCLs. Michigan’s inclusion of PFNA and PFDA—long-chain PFAS added to the Stockholm Convention—reflects the state’s extensive history with PFAS contamination from 3M and other chemical manufacturing operations in the western part of the state, where legacy contamination of drinking water wells has affected thousands of residents.
Vermont: 10 ppt for Five Compounds
Vermont established MCLs of 10 ppt each for five PFAS compounds: PFOA, PFOS, PFHxS, PFNA, and PFHpA. Vermont’s MCLs apply to all regulated public water supplies in the state and are enforced by the Vermont Department of Environmental Conservation (VTDEC). Vermont’s standard for PFHxS and PFNA at 10 ppt each is notable because these are precisely the compounds for which the federal EPA proposed MCL rescission in 2025—meaning Vermont’s standard provides continued protection for these compounds regardless of what happens at the federal level.
California: 5 ppt for PFOA and PFOS
California’s State Water Resources Control Board finalized PFAS MCLs of 5 ppt for PFOA and 5 ppt for PFOS—slightly more stringent than the federal 4 ppt MCLs. California also established response levels and notification levels for additional PFAS compounds including PFBS, PFHxS, and PFNA that require water system action—public notification and provision of alternative water—when detected above specified concentrations, even in the absence of formally adopted MCLs for those compounds. California’s regulatory approach reflects the state’s history with contamination from military installations, firefighting training areas, and manufacturing facilities, as well as its strong public health culture and willingness to regulate chemicals ahead of federal action.
New Hampshire: Among the Earliest State MCLs
New Hampshire established PFAS MCLs in 2019—among the earliest in the nation—setting limits of 15 ppt for PFOA, 15 ppt for PFOS, 11 ppt for PFNA, and 18 ppt for PFHxS. These standards were established before the scientific and regulatory consensus crystallized around lower values, and New Hampshire is expected to revise them downward in the coming years to align more closely with federal and peer-state standards. New Hampshire’s early action was driven by documented contamination of drinking water wells near Pease International Tradeport, a former military air base in Portsmouth, New Hampshire, that became one of the first high-profile AFFF contamination sites in the United States.
The Commercial Significance of State MCLs
For OEM filter manufacturers and water treatment system suppliers, the practical significance of state MCLs cannot be overstated. The states with the most stringent PFAS MCLs—Massachusetts, Michigan, Vermont, and California—are also among the largest and most economically significant U.S. markets for municipal water treatment equipment. Municipal procurement specifications in these states reference the state MCLs as the performance benchmark for treatment systems, meaning that activated carbon media, ion exchange resin columns, and membrane systems must demonstrate reduction of the relevant compound suite to below each state’s specific limits. Manufacturers that develop certified performance data specifically tailored to Massachusetts’s sum-of-six standard, Michigan’s seven-compound standard, or Vermont’s five-compound standard will have a commercial advantage in these high-value markets regardless of changes to federal MCLs.