Almost half the tap water in the United States contains PFAS, a class of chemicals linked to serious health problems. On Wednesday, the Environmental Protection Agency announced that, for the first time, municipal utilities will have to detect and remove PFAS from drinking water. Here’s what you need to know. What are PFAS? Sign up for The Morning newsletter from the New York Times In 1938 a young chemist working on refrigerants for Dupont accidentally discovered a new compound that was remarkab