Similar stories abound. In February failed pipes at a Duke Energy dump sent tens of thousands of tons of hazardous coal ash into the Dan River in Eden, N.C., which supplies the drinking water for communities in both North Carolina and Virginia. Industrial and agricultural chemicals show up repeatedly in groundwater that serves millions of Californians. Nationwide, 19 million Americans become sick every year from viruses, bacteria and parasites that sneak through ineffective municipal drinking-water treatment plants, according to a New York Times investigation.