And you thought the biggest problem with D.C. water was the possible lead contamination. The Environmental Working Group will release a study Monday showing that out of 35 cities surveyed, 31 have hexavalent chromium in their tap water. You might have heard of hexavalent chromium, as you might remember by Erin Brockovich, who sued the Pacific Gas & Electric in California when the possible carcinogen was found in Hinkley, CA’s water supply.