What happened
In April 2024, the EPA finalized the first enforceable U.S. drinking water limits for six per- and polyfluoroalkyl substances (PFAS). For PFOA and PFOS — the two most extensively studied compounds — the Maximum Contaminant Level was set at 4 nanograms per liter (parts per trillion), the lowest concentration the agency considers technically measurable in routine testing.
The other four regulated compounds — PFHxS, HFPO-DA (GenX), PFNA, and PFBS — are subject to a combination of individual limits and a "Hazard Index" approach for mixtures.
Utilities had until 2027 to begin compliance sampling and have until 2029 to implement treatment if they exceed the MCLs. EPA estimates capital and operating costs to the U.S. water sector at approximately $1.5 billion per year — though independent estimates from utility associations run higher.
In late 2024, the American Water Works Association and a consortium of large utilities filed suit in the D.C. Circuit, arguing that EPA's cost-benefit analysis underestimated implementation costs and that the limits are set below what is scientifically justified. As of this writing, the rule remains in force pending litigation.
Our take
The 4 ng/L limit is striking for what it implicitly concedes: EPA's MCLG (Maximum Contaminant Level Goal) for PFOA and PFOS is zero, and the agency has set the enforceable MCL at the lowest level it considers practically measurable. In plain terms: the agency is saying any detectable PFOA or PFOS is too much.
That is a defensible position on the health evidence. PFOA is now classified by IARC as a Group 1 human carcinogen, and the C8 Health Project (cohort of ~70,000 Ohio Valley residents) established dose-response relationships at exposure levels comparable to what many U.S. utilities are now finding.
The legitimate concern about the rule is not that it is too strict — the health science supports stringency — but that it will take time, money, and infrastructure investment that small rural systems particularly will struggle to absorb. The compliance timeline through 2029 is calibrated for large municipal systems; a 1,500-connection system in rural Pennsylvania is in a different position.
What this means for readers: PFAS compliance sampling is just beginning in most utilities. Your utility's current report almost certainly does not reflect what it will report by 2029. If you live in a known impacted area, do not wait for the regulatory cycle to act.
Sources
- EPA. PFAS National Primary Drinking Water Regulation (Final Rule).
- USGS. PFAS in U.S. Tap Water (2023).
- ATSDR. Toxicological Profile for Perfluoroalkyls.