In the absence of an enforceable federal drinking water standard for per- and polyfluoroalkyl substances (“PFAS”), many states have started regulating PFAS compounds in drinking water. The result is a patchwork of regulations and standards of varying levels, which presents significant operational and compliance challenges to impacted industries. This client alert surveys the maximum contaminant levels (“MCLs”), as well as guidance and notification levels, for PFAS compounds – typically perfluorooctane sulfonate (“PFOS”) and perfluorooctanoic acid (”PFOA”) – in drinking water across the United States.