Public water systems should test and monitor for the chemical chromium-6 on a regular basis. That’s the advice from the Environmental Protection Agency. Chromium-6 (hexavalent chromium) attracted worldwide attention from the movie “Erin Brokovich” and a recent study found the cancer-causing metal in the tap water of more than two dozen cities. The EPA’s new guidelines encourage quarterly or semi-annual testing for the metal. The advice is not binding but could be a first step toward national limits that help reduce cancer risk from exposure to contaminated water. Right now the EPA requires testing only for total chromium, which includes chromium-6. The agency has promised to complete a full scientific review of chromium-6 by this summer. A recent draft concluded that ingesting the metal in drinking water is likely to be carcinogenic in humans. The EPA’s latest data show that no water system is in violation of the current standards for total chromium. But a recent study by the non-profit Environmental Working Group found the chemical in tap water from 31 of 35 cities tested.