What the 2024 PFAS MCL Rule Establishes
In April 2024, the U.S. Environmental Protection Agency finalized the first-ever national primary drinking water regulations for PFAS. The rule establishes maximum contaminant levels (MCLs) for six PFAS compounds: PFOA and PFOS at 4 parts per trillion (ppt) each; PFNA, PFHxS, and HFPO-DA (GenX) at 10 ppt each; and a hazard index of 1 for mixtures of PFNA, PFHxS, HFPO-DA, and PFBS.
The 4 ppt MCLs for PFOA and PFOS represent the lowest technically and analytically feasible limits — at or near the detection limits of the most sensitive laboratory methods. This approach reflects EPA’s determination that no safe level of these carcinogenic compounds can be established.
Who Must Comply and By When
All public water systems that serve 15 or more connections or 25 or more people year-round must comply with the new standards. This covers approximately 66,000 public water systems serving 93% of the U.S. population. Systems must complete initial monitoring within three years and achieve compliance within five years of the rule’s effective date — by 2029.
The EPA estimated that 6–10% of public water systems may have PFAS levels exceeding the new MCLs, requiring treatment upgrades. Granular activated carbon (GAC) and reverse osmosis are the most commonly used treatment technologies at the utility scale.
Funding and Implementation Challenges
The Infrastructure Investment and Jobs Act provided $10 billion specifically for emerging contaminants including PFAS, which will help utilities finance treatment system upgrades. Smaller utilities, which often have less financial capacity, are eligible for state revolving fund assistance.
Industry groups challenged the rule in federal court, arguing that the MCLs are technically and economically infeasible. Legal challenges could delay implementation, though EPA has broad authority under the Safe Drinking Water Act to set standards protective of public health.