Protect Drinking Water from PFAS Act of 2021 This bill requires the Environmental Protection Agency (EPA) to address the level of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in drinking water. PFAS are man-made and may have adverse human health effects. A variety of products contain PFAS, such as nonstick cookware or weatherproof clothing. The EPA must publish a maximum contaminant level (MCL) and promulgate a national primary drinking water regulation for PFAS that includes perfluorooctanoic acid (commonly referred to as PFOA) and perfluorooctane sulfonic acid (commonly referred to PFOS). The MCL and regulation must be protective of the health of subpopulations that may be at greater risk than the general population of adverse health effects from exposure to PFAS in drinking water.