The District will protect the health and safety of the public in its service area, protect the quality of the water supply source (Lake Michigan), improve the quality of water in watercourses in its service area, protect businesses and homes from flood damages, and manage water as a vital resource for its service area. The District’s service area is 883.5 square miles of Cook County, Illinois. The District is committed to achieving the highest standards of excellence in fulfilling its mission.
  The District’s seven modern water reclamation plants provide excellent treatment for residential and industrial wastewater, meeting permitted discharge limits virtually at all times. The treatment process is protected by a pretreatment program to guard against hazardous substances and toxic chemicals. These are strictly regulated pursuant to federal and state requirements. The District routinely monitors all industries and non-residential sources to assure that wastes are disposed of in an environmentally responsible and lawful manner.

Treated wastewater, along with runoff from rainfall, enters local canals, rivers and streams that serve as headwaters of the Illinois River system. Stormwater in the separate sewered area is controlled to reduce flood damages by a number of stormwater detention reservoirs. In the combined sewer area, the District’s tunnel and reservoir project has significantly reduced basement backup and overflows to local waterways.

Flow within the District’s waterway system and the Lake Michigan discretionary diversion flow are controlled by three inlet structures on Lake Michigan: Wilmette Pumping Station, Chicago River Controlling Works and O’Brien Lock and Dam. The single outlet control structure is the Lockport Powerhouse and Controlling Works.

While exercising no direct control over wastewater collection systems owned and maintained by cities, villages, sewer districts and utilities, the District does control municipal sewer construction by permits outside the city of Chicago. It also owns a network of intercepting sewers to convey wastewater from the local collection systems to the water reclamation plants.


The District is located primarily within the boundaries of Cook County, Illinois. The District serves an area of 883 square miles which includes the city of Chicago and 128 suburban communities. The District serves an equivalent population of 10.35 million people; 5.25 million real people, a commercial and industrial equivalent of 4.5 million people, and a combined sewer overflow equivalent of 0.6 million people. The District’s 560 miles of intercepting sewers and force mains range in size from 6 inches to 27 feet in diameter, and are fed by approximately 10,000 local sewer system connections.

The District’s Tunnel and Reservoir Project (TARP) is one of the country’s largest public works projects for pollution and flood control. Four tunnel systems total 109 miles of tunnels, 8 to 33 feet in diameter and 150 to 300 feet underground. The Majewski and Thornton reservoirs are in operation, while the first phase of construction on the McCook Reservoir is scheduled for completion in 2017.

The District owns and operates one of the world’s largest water reclamation plants, in addition to six other plants and 22 pumping stations. The District treats an average of 1.4 billion gallons of wastewater each day. The District’s total wastewater treatment capacity is over 2.0 billion gallons per day.

The District controls 76.1 miles of navigable waterways, which are part of the inland waterway system connecting the Great Lakes with the Gulf of Mexico. It also owns and operates 34 stormwater detention reservoirs to provide regional stormwater flood damage reduction. The District owns approximately 9,500 acres of property in Cook County for its operations.

In conjunction with its biosolids beneficial utilization and farm land application program, the District recycles all biosolids in land application programs in northeast Illinois, and owns over 13,500 acres of land in Fulton County, Illinois, formerly used for biosolids application.