Probable Carcinogen Hexavalent Chromium Found In Drinking Water Of 31 U.S. Cities  An environmental group that analyzed the drinking water in 35 cities across the United States, including Bethesda and Washington, found that most contained hexavalent chromium, a probable carcinogen that was made famous by the film "Erin Brockovich." Hexavalent chromium was a commonly used industrial chemical until the early 1990s. It is still used in some industries, such as in chrome plating and the manufacturing of plastics and dyes. The cities were selected to be a mix of big and smaller communities and included places where local water companies had already detected high levels of "total chromium."