The Long Journey Begins
The water’s journey begins two miles off the Chicago shoreline in Lake Michigan at water intake structures called “cribs.” These cribs, located in 35-foot deep water, have served the Chicagoland area since their construction about 100 years ago.
Lake Michigan water enters the cribs through openings 20 feet below the lake’s surface. The water rises around the outside of a large pipe inside the crib then flows through a 20 foot diameter tunnel to the James W. Jardine Water Purification Plant, the largest water treatment plant in the world, located just north of Chicago’s Navy Pier.
Upon reaching the plant, the water is pumped to a height of about 20 feet above lake level. Water flows, by gravity, through the chemical application channels and basins of the plant. In the treatment channel, chemicals like alum are added to collect and remove impurities from the water. Powdered activated carbon is added as necessary to improve taste and remove odors, enhancing the quality of the water. The initial dosage of chlorine is added to kill bacteria.
Next, the water flows into chambers called flocculation basins. Here large paddles stir the water slowly to form flocs, clusters of impurities that look like snowflakes. The water then moves to the settling basin, where these floc molecules sink to the bottom and are removed.
The final steps in the purification process take place in the filtration chamber where filters trap any remaining impurities. Fluoride is then added to help prevent tooth decay. The water then flows to reservoirs where it is stored until needed. A small amount of additional chlorine is added before leaving the treatment plant.
This filtration and purification process takes approximately eight hours, producing water that meets or exceeds all water quality standards established by federal and state agencies.