WASHINGTON - Some water utility representatives have protested Environmental Working Group’s report of laboratory tests that found worrisome levels of chromium-6, a suspected carcinogen, in the drinking water of 31 cities across the country.

Yet the tap water industry was worried enough about the contaminant to conduct its own extensive survey in 2004 that found clear evidence of widespread chromium-6 pollution in untreated source water. The survey, conducted by the Awwa Research Foundation (since renamed the Water Research Foundation), an offshoot of the American Water Works Association, obtained data on 341 source water samples from 189 utilities in 41 states. The conclusion: chromium-6 is common in American groundwater.

Tap water industry representatives made no mention of their study when they testified alongside EWG at a Feb. 2 Senate environment committee hearing on chromium-6 pollution. There is no indication that customers of the189 participating utilities were advised of the chemical’s presence in source waters in their communities.

Chromium-6, also known as “hexavalent chromium,” is often called the “Erin Brockovich” chemical, after the crusading legal assistant who helped residents of tiny Hinkley, Calif, win a $333 million settlement from Pacific Gas & Electric Co, accused of dumping the chemical in local ground water. Actress Julia Roberts won an Oscar for her portrayal of Erin Brockovich in the 2000 film of the same name.

The 2004 industry study, which EWG obtained from a source and cited in its December 2010 report, Cancer-causing Chromium-6 Pollution in U.S. Tapwater, demonstrates that chromium-6 pollution was not confined to California.

“The tap water industry’s 2004 study is unmistakable proof that it has known about extensive chromium-6 contamination for at least seven years,” said Jane Houlihan, EWG senior vice president for research. “Water utilities should tell their customers any time they know that a suspected carcinogen has polluted local waters. People have a right to know what they and their families may be drinking.”

“I’d like to say I’m surprised at the utilities’ silence, but I’m not,” Brockovich said. “Instead of treating their customers like adults and sharing the test results with them, they shelved the findings, letting folks continue to drink water for years that could contain chromium-6.”

Pollution levels in untreated and treated water are not directly comparable. Even so, the two studies, read together, paint a picture of coast-to-coast chromium-6 pollution.

The industry research group provides its report Occurrence Survey of Boron and Hexavalent Chromium to water utilities and their consultants, who pay four or five-figure subscription fees and a document fee of about $300. (The report can now be bought online for $200 or more.)