City of Chicago

The City of Chicago continuously monitors for Cryptosporidium, Giardia and E. coli in its source water as part of its comprehensive quality program. While Cryptosporidium hasn't been detected in recent samples, Giardia was identified in one lake water sample collected in September 2010.

Treatment facilities have been optimized to create effective barriers for removing these organisms from source water. By maintaining low turbidity through particle filtration, the risk of Cryptosporidium and Giardia entering the water system is significantly reduced.

In 2017, the Department of Water Management (DWM) continued monitoring for hexavalent chromium (chromium-6), a contaminant of concern with both natural and industrial sources. The EPA hasn't yet established standards for chromium-6. Questions about this monitoring program can be directed to DWM's Water Quality Division at 312-742-7499.

Data reports on chromium-6 monitoring are available on the City's website at http://www.cityofchicago.org/city/en/depts/water/supp_info/water_quality_resultsandreports/city_of_chicago_emergincontaminantstudy.

SOURCE WATER ASSESSMENT
The Illinois EPA implemented a Source Water Assessment Program (SWAP) to assist with watershed protection. The SWAP inventories potential contamination sources and evaluates source water vulnerability. The Illinois EPA has completed this assessment for Chicago's water supply.

WATER SOURCE LOCATION
Chicago utilizes Lake Michigan as its water source through two treatment plants. The Jardine Water Purification Plant serves northern areas of the city and suburbs, while the South Water Purification Plant serves southern regions. Lake Michigan is the only Great Lake entirely within the United States, bordering Illinois, Indiana, Michigan, and Wisconsin. It's the second largest Great Lake by volume (1,180 cubic kilometers) and third-largest by area.

CONTAMINATION VULNERABILITY
The Illinois EPA considers all surface water sources for community supply to be susceptible to potential pollution. Surface water allows contaminants to migrate into intakes with only dilution as protection, necessitating mandatory treatment for all surface water in Illinois.

Chicago's offshore intakes are positioned at distances where shoreline impacts aren't typically considered factors affecting water quality. However, in wet weather conditions, the potential for contamination exists due to runoff and water reversals. Additionally, crib structures may attract waterfowl, potentially compromising source water quality through waste deposits. The shoreline intakes are particularly vulnerable to storm water runoff, marina activities, and direct shoreline sources due to groundwater flow toward the lake.

1. What contaminants are most concerning in Chicago's water supply?
   The most concerning contaminants include trihalomethanes (TTHMs), chromium-6, and potential traces of 1,3-Butadiene, Phenanthrene, and Ethylene dibromide.
2. How does Chicago treat its municipal water?
   Chicago employs multi-stage treatment including filtration, disinfection, and chemical treatment to remove contaminants and pathogens from Lake Michigan water.
3. Is Chicago water considered hard or soft?
   Chicago water is considered moderately hard, containing dissolved minerals like calcium and magnesium that can cause scale buildup in pipes and appliances.
4. How often is Chicago's water tested?
   The City of Chicago conducts thousands of tests monthly, checking for regulated contaminants, emerging compounds, and microbial threats in both source and treated water.
5. Should Chicago residents use water filters?
   While Chicago's water meets federal standards, some residents choose to use filters to address concerns about lead from old plumbing, taste preferences, or specific health sensitivities.