An invisible contamination problem has been brewing in America’s underground water supplies for decades. New research from the U.S. Geological Survey has finally mapped its extent, showing that between 71 and 95 million Americans rely on groundwater containing detectable levels of “forever chemicals,” synthetic compounds linked to cancer, fertility issues, and other health problems. This research, published in Science, includes a first-of-its-kind map that comes as public awareness about these contaminants grows.