As a precaution, the Chicago Department of Water Management said people who live in the 4600- and 4700-blocks of West Patterson Avenue should not drink their water or use it to prepare food or wash dishes.
City officials said Friday that the issue has been resolved by flushing the water mains and the "do not drink" order was lifted.
As part of its investigation, the Water Department said that two car washers in the area were operating without proper backflow devices. They have been closed and will remain closed until the problems have been corrected.