Chicago Water Department Facilities (page 2)
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 flocs 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. Chlorine and fluoride are then added: chlorine to kill bacteria, fluoride to help prevent tooth decay. The water then flows to reservoirs where it is stored until needed. 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.

Treated water leaves the reservoirs at the Jardine Plant and flows to eight pumping stations located throughout Chicago. The water serving DuPage County initially flows to the Central Park Pumping Station. Central Park is where the Commission first tapped in the Chicago lake supply.