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OKLAHOMA CITY – An advocacy group is warning residents in some Oklahoma towns about potential dangers lurking in the tap water.

The group claims to have found dangerous levels of chromium-6 in contaminated tap water, which is being consumed by hundreds of millions of Americans.

Chromium-6 is the same cancer causing chemical featured in the 2000 movie “Erin Brockovich,” starring Julia Roberts.

The group analyzed water systems throughout the United States and found the tap water of 218 million Americans contains levels of chromium-6.

The group says that is dangerous.

Of all the cities tested, Oklahoma City and Phoenix had the highest levels of contamination, by far.

The EPA did not directly address the report, but did say the agency is working on a healthy assessment of chromium-6.

So far, the EPA has not set a specific standard on the chemical for drinking water.

Click here to see the levels from the study.