The U.S. EPA recommends that public water systems can enhance monitoring and sampling programs for hexavalent chromium through regular sampling. Surface water systems are encouraged to sample quarterly, and groundwater systems semiannually.

Among its recommendations are to collect samples at the intake or well, at the point that treated water enters the distribution system, and at up to 10 of the same locations that systems sample under the Disinfection By-Products Rule Stage 1 and 2.

The announcement comes in light of a December 2010 report that found that tap water from 31 of 35 U.S. cities tested contains chromium-6, popularized by the 2000 movie Erin Brockovich, according to the Environmental Working Group, a Washington, D.C.-based nonprofit advocacy group.

Until recently, the compound hadn't been viewed as an immediate threat in drinking water by EPA. Its latest six-year review of drinking water standards in March 2010 determined that the limit remained acceptable.