Last year, the Environmental Protection Agency set the first federal drinking water limits for PFAS, or perfluoroalkyl and polyfluoroalkyl substances, finding they increased the risk of cardiovascular disease, certain cancers and babies being born with low birth weight.

In a decision with consequences for tens of millions of Americans, the Trump administration is expected to soon say whether it intends to stand by those standards and defend the limits against a water utility industry challenge in federal court.

So far, sampling has found nearly 12 percent of water utilities are above the recently set EPA limits, but most aren’t above by much. Forcing this group to reduce PFAS more than doubles the rule’s health benefits but roughly triples its costs, the EPA has said.

The Biden administration’s rule set standards for two common types of PFAS at 4 parts per trillion, effectively the lowest level at which they can be reliably detected. Standards for several other PFAS chemicals were set, too, and utilities must meet those levels by 2029.

EPA Administrator Lee Zeldin has championed fossil fuels and the rollback of major clean air and water rules. His history with PFAS is more nuanced; during his time as a New York congressman, he supported legislation to regulate forever chemicals in drinking water.

Zeldin has offered clues about what the EPA could do. The agency estimated the rule would cost about $1.5 billion annually and Zeldin said recently that communities struggling to afford a fix for PFAS that are just above the standard might be handled differently than wealthy places with lots of it.

The EPA said this week it will establish an agency lead for PFAS, develop wastewater limits for PFAS manufacturers and investigate sources that pose an immediate danger to drinking water, among other actions.

Soon, the EPA must tell a federal appeals court in Washington whether the rule should stand or be rewritten, although weakening it could be complicated because the Safe Drinking Water Act prevents new rules from being looser than previous ones. The agency could, however, encourage exemptions and deadline extensions, according to Erik Olson, an attorney with the non-profit Natural Resources Defense Council supporting the current standards in the court case.

The American Water Works Association, an industry group, filed the court challenge to the new rule. It agrees that certain PFAS should be regulated, but argues the EPA’s standards go too far, underestimate costs and are “neither feasible nor cost-effective.”