In 2007, the former Department of Environment (DOE) conducted a potable well survey to determine if active potable wells exist in and nearby the city limits. Information was obtained from the Illinois State Geological Survey (ISGS) regarding all confirmed records of wells installed within the City limits of Chicago and 200 feet beyond. The well search revealed three categories of wells: community water supply wells (CWS); public, non-CWS wells; and private wells.

The well records available from the ISGS and the City’s Department of Water Management were reviewed and it was determined that most water wells listed within the city and a 200-foot buffer zone of city limits are no longer in use. Two community water supply wells are confirmed in use outside of the city limits. Twenty-nine wells identified as public, non-community water supply wells and twelve wells identified as private are located within Cook County forest preserve areas. The existence or utilization of these wells was not confirmed. A total of 1,436 private well records were evaluated and the status of sixteen wells, on the edge or outside the city limits, cannot be confirmed. DOE believes that all other wells classified as water wells either do not exist or are no longer in use.