In Chicago's first round of testing for the toxic metal contaminant, results show that the city's local drinking water contains levels of hexavalent chromium more than 11 times higher than the health standard set in California last month.
Some researchers claim there is strong evidence showing exposure to the contaminant may lead to stomach cancer.
The metal's health risk has long been the subject of debate, with industrial polluters and municipals water utilities lobbying to block delay of the Obama Administration's push for national regulations, reports the Chicago Tribune.
Debates over dozens of unregulated substances have renewed as studies ensue over the heath threats of different industry chemicals, pharmacetical drugs and herbicides.
Test results revealed the Lake Michigan water pumped to seven million people in Chicago and the suburbs contained .23 parts per billion of the toxic metal.
California's Office of Environmental Health Hazard Assessment designated the nation's new "public heath goal" limit as .02 parts per billion.
Studies also suggest that exposure to the metal increases risk of reproductive problems, could interfere with childhood development or may cause liver and kidney damage.
Chicago officials stress that local tap water is safe and said that should a national limit be adopted, the goal would be less stringent than California's standard.