Public water supplies may be large, like the Great Lakes Water Authority, which serves 3.7 million residents, or they may be smaller, such as a supply serving a manufactured housing community. Some public water supplies get water from groundwater, some from surface waters (lakes or rivers) and some blend groundwater and surface water sources together. To ensure the drinking water for the largest portion of Michigan residents was tested for PFAS, beginning in April 2018, the Michigan Department of Environment, Great Lakes, and Energy (EGLE) implemented a statewide program to test Michigan's public water supplies across several phases of sampling.
The United States Environmental Protection Agency (USEPA) set a Lifetime Health Advisory (LHA) level for two PFAS in drinking water: perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) . The LHA level is 70 parts per trillion (ppt, equal to 70 ng/L) for PFOA and PFOS combined, or individually if only levels for other PFAS chemicals. The State of Michigan is using 70 ppt for decision making purposes.
Only two supplies were found to have PFOS+PFOA over the USEPA LHA: