The toxic class of chemicals known as PFAS can cause serious health problems, including birth defects and some cancers. So scientists, health experts, and policymakers have been working to reduce our exposure.

Pennsylvania and Delaware recently announced proposals to establish maximum contaminant levels, or MCLs, for the compounds in drinking water. (New Jersey already has them.) That would require water providers to ensure that levels of PFAS in their supplies remain below a certain threshold.

But protecting people’s health has a consequence: The technology most effective at removing PFAS contributes to the carbon footprint.