updated: Report: Chromium-6 detected in Ann Arbor drinking water

The report lists 31 U.S. cities where people could be drinking contaminated tap water. Ann Arbor is 12th on that list with levels at .21 parts per billion.

According to the group, the EPA doesn’t require testing for chromium-6 and hasn't established any legal threshold for how much of it can be in drinking water. It is, however, classified as a probable human carcinogen.

Molly Wade, water treatment services manager for the city, said Ann Arbor tests its water supply yearly for various types of chromium, though the EPA requires testing only every nine years. The detection limit for the test they use is 2 parts per billion. The levels of all chromium read "non-detect," which means they are under 2 ppb, she said.

The city runs thousands of additional tests on its water every year, Wade said — for everything from bacteria to metals and gasoline byproducts. Some of the tests occur daily.

Wade said the city sends its water samples for chromium tests to an Underwriters Laboratory site in Indiana. UL is an independent product safety certification organization.

The Environmental Working Group didn't work with the city on testing samples, and Wade said she isn't sure where they did their testing.

"Our water meets or exceeds all state and federal standards," Wade said. "We're confident about our drinking water supply."

The group's report notes most people aren't familiar with chromium-6, but they might be familiar with the Erin Brockovich story. Tainted groundwater prompted Brokcovich to help bring about a lawsuit and a $333 million settlement for Hinkley, Calif., residents impacted by the chemical.