Per- and polyfluoroalkyl substances (PFAS) are a diverse group of human-made chemicals used in a wide range of consumer and industrial products. These chemicals seep into water from factories, landfills, and other sources. They’re often called "forever chemicals" because they don’t easily break down in the environment. PFAS chemicals have been linked to many adverse health outcomes, including kidney and testicular cancer, thyroid problems, liver disease, decreased fertility, and developmental problems.