We have previously detailed the EPA’s efforts under the Biden Administration to regulate certain types of PFAS under the Safe Drinking Water Act. In short, PFOA and PFOS would have a Maximum Contaminant Level of 4 ppt, and PFHxS, PFNA, HFPO-DA and certain mixtures would either have a 10ppt limit or would be tested by using the EPA’s Hazard Index approach. Almost immediately, the PFAS drinking water rule was challenged in court and the case has lingered in the D.C. Circuit Court for about 18 months.

The biggest reason for the delay, however, was due to the fact that a new Administration took over in January 2025, and the EPA requested several continuances to assess whether it wished to proceed with the full scope of the Biden EPA’s PFAS drinking water rule. After several months, the EPA moved the Court to vacate all but the PFOA and PFOS portion of the rule.

On January 21, 2026, the Court issued a very brief Order denying the EPA’s request to vacate any part of the PFAS drinking water rule. The Court’s reasoning for denying EPA’s request was simple and brief: “The merits of the parties’ positions are not so clear as to warrant summary action.” As such, the case will now go to a merits panel for ultimate decision on the fate of the PFAS drinking water rule.

Since the Court’s ruling, the EPA filed a Motion to sever and stay the issue of whether the Hazard Index PFAS should remain as regulated under the Safe Drinking Water Act. Working off of quick deadlines for briefing, an Opposition and EPA Reply brief have subsequently been filed. In short, the EP argues that the Hazard Index issue should be handled separately because doing so would lead to judicial efficiency. EPA contends that the Hazard Index issues in particular are incredibly complex, as they deal with detailed statistical studies and scientific analyses of how each of the Hazard Index PFAS effect certain endpoints in the human body. EPA notes “petitioners have challenged all of these issues and, while it is certainly true that counsel of record are deeply steeped in them, there is no reason the Court should expend resources wading into this morass when EPA is actively engaged in a rulemaking that could obviate the need for judicial review of this record.” Opposition arguments also focus on judicial economy, but they argue that staying the Hazard Index analysis indefinitely does not promote judicial economy. Further, water utilities in particular would be prejudiced, as they still must operate under the assumption that the Hazard Index PFAS regulations are in effect and so they must invest incredible amounts of time and money into planning for compliance with the Hazard Index approach.

The ongoing challenge to the rule continues the uncertainty that many entities, including water utilities, states, and corporations, have felt for several years now in terms of where PFAS drinking water regulations will ultimately land. Water utilities especially are under duress to try to figure out not only what regulation will need to be complied with, but also what technology needs will be required. States are left uncertain as to whether a PFAS regulation that some states prefer to see enacted at the federal level will be stripped in some way, leaving the states as the stopgap measure to enact state-level regulations of their own. Corporations concerned about legacy uses (whether intentional or not) of PFAS and water discharges that may have contaminated drinking water sources must also wait to see the full scope of PFAS that they should conduct historical diligence on to assess risk.

It appears likely that the fate of the PFAS drinking water regulation will be decided by the second half of 2026, so the best course of action for any of these entities remains one of continued due diligence appropriate for their specific needs.

CMBG3 Law is following judicial, legislative, administrative, and scientific developments relating to PFAS. More information about the services we can provide, including litigation defense, compliance guidance, and risk assessments can be found on our PFAS Litigation page. Our attorneys have been at the forefront of PFAS issues, including giving presentations as to the future waves of litigation stemming from PFAS issues, and currently represent numerous companies related to PFAS litigation or consulting. For more information, please contact the Chair of our PFAS Team: John Gardella.