The U.S. Environmental Protection Agency found that half of the Chicago homes it visited last fall had lead levels in their tap water high enough to warrant federal regulatory action. No action is being taken right now -- but the findings might lead the U.S. EPA to update how it tests tap water for lead.

Usually, federal regulators just look at the first liter of water to come out of tap water faucets. But, as the Chicago Tribune reports, the tests conducted this fall, all done at the home of federal employees, found potentially dangerous levels of the toxic metal in subsequent liters.

Chicago water can become tainted with lead as it goes from the treatment plant through water service lines.