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  • James Howey

Chicago Water Supply

Is it nerdy to go and look at ‘water stuff’ when you’re on holiday? No, of course not, here’s what I have found out about Chicago’s water supply with some snaps.

Chicago sits on Lake Michigan, and sources its drinking water from this, the second largest of the Great Lakes. A key feature are the cribs that are visible from the waterfront, which are the structures that house the offshore intakes.

These circular stone structures protect intake vents that connect with brick-lined passageways buried 200 feet under Lake Michigan. Water is collected and transported through tunnels located beneath the lake. The tunnels lead from the water cribs to one of two water purification plants located onshore, the world’s largest water treatment plant, the Jardine Water Purification Plant and the Eugene Sawyer Water Purification Plant. The city has had nine permanent cribs of which six are still standing and two are in active use.

Treatment Processes

  • Water from Lake Michigan enters the intake crib at depths of 20 to 30 feet.

  • Water enters the purification plant's intake basin through a tunnel beneath the lakebed.

  • Water is filtered through eight traveling screens to catch debris.

  • Water is pumped by low lift pumps up to 25 feet for the first chemical treatment.

  • Water flows from the chemical application channels.

  • Water flows through mixing basins to begin the flocculation process.

  • Flocculated water passes into settling basins to sit for hours allowing floc to settle.

  • Water is filtered through precisely graded sand and gravel performing a "natural polishing".

  • Filtered water flows into clear wells for its final chemical application.

  • From finished water reservoirs water flows to the distribution system.

Chemical dosing includes:

Chlorine, alum and polymer, blended polyphosphate (to coat pipes and prevent lead leaching), Activated Carbon and Fluoride.


Initially, the city used the lake to both supply water and to dispose of wastes. Chicago suffered many outbreaks, with a widespread cholera outbreak in 1885 which killed one in eight residents!

Efforts to keep the lake's water supply from contamination by the Chicago River led to the reversal of the river's flow with the deep cut of the Illinois & Michigan Canal in 1871 and the construction of the Sanitary and Ship Canal at the turn of the century.

In 1900, the Sanitary District of Chicago completed the 28-mile Sanitary and Ship canal to reverse the flow of the Chicago River (and the wastewater discharges) away from Lake Michigan, thereby improving the quality of lake water. This canal reversed the flow in the Chicago River toward the Mississippi River and Gulf of Mexico, diverting sewage away from the Lake Michigan water supply. Even though it was considered a great benefit for Chicago, cities along the Des Plaines, Illinois and Mississippi Rivers, especially St. Louis, were not so happy at the thought of drinking Chicago's sewage.

In addition to changes to the wastewater, the Ellis Chesbrough's Chicago Water Supply System was the first major system to utilize offshore intake systems, to take advantage of the better quality of water located away from the city. The system includes the cribs, tunnels and the landmark Chicago Water Tower and the Chicago Avenue Pumping Station.

The first lake tunnel was completed in 1869 and connected to the Water Tower and Pumping Station at Chicago and Michigan Avenues. Today, multiple lake tunnels and pumping stations constitute Chicago's water system.

The Jardine Water Treatment Plant, located just north of the city centre is the largest capacity filtration plant in the world and can treat a million gallons of water a minute, has 96 Olympic swimming pool size filters and provides drinking water to 5.5 million people in Chicago and surrounding suburbs.

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