Tests of Chicago's drinking water turned up low levels of the bug repellent DEET, the Chicago Sun-Times said.
Health experts said the concentration found in the newspaper's sampling -- 8.3 parts per trillion-- shouldn't prose a health hazard, although Duke University Professor Mohamed Abou-Dania said the finding raises a red flag.
The Chicago Tribune reported last week that trace amounts of prescription drugs and other unregulated chemicals were found in the local tap water, which comes from Lake Michigan.
There are no federal standards requiring the removal of DEET or other contaminants such as pharmaceuticals, flame retardants and plasticizers, the Sun-Times said.
Chicago water officials said they are testing untreated Lake Michigan water and finished drinking water for chemical compounds to build a baseline database.
John Spatz, commissioner of the Department of Water Management, said the water is safe to drink.
"The last thing we want is to erode confidence in the public water supply," he told the Sun-Times.
Copyright 2008 by United Press International
Explore further: Measuring the height of the world's forests