On March 14, the U.S. Environmental Protection Agency (EPA) provided a pre-publication version of a proposed National Primary Drinking Water Regulation Rulemaking that would regulate six polyfluoroalkyl substances (PFAS) under the Safe Drinking Water Act, 42 U.S.C. Sections 300f et seq (PFAS rule). The proposed PFAS rule would establish maximum contaminant level goals (MCLGs) and maximum contaminant levels (MCLs) for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), two of the most common PFAS—a group of thousands of manmade chemicals used in various consumer, commercial and industrial manufacturing processes since the 1940s—as individual contaminants. It would also establish a hazard index MCL for mixtures containing one or more of perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid and its ammonium salt (HFPO-DA, commonly known as GenX chemicals), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS). Years in the making, the final PFAS rule will be the first federally enforceable drinking water rule governing PFAS. The EPA intends to finalize the PFAS rule by the end of 2023.