PFAS Health Study Act of 2021 This bill extends through FY2023 the authority of the Department of Defense to transfer funds for the required study on the human health implications of perfluoroalkyl and polyfluoroalkyl substances (PFAS) contamination in drinking water, groundwater, and any other sources of water and relevant exposure pathways, including the cumulative human health implications of multiple types of PFAS contamination at levels above and below health advisory levels. PFAS are man-made and may have adverse human health effects. A variety of products contain the compounds, such as nonstick cookware or weatherproof clothing.