FAQs

A combined sewer system conveys both sanitary sewage and storm water in one piping system. The District's combined sewer system was developed before 1900. Separate systems are comprised of two independent piping systems: one system for "sanitary" sewage (i.e., sewage from homes and businesses) and one system for storm water. The figure below and following paragraphs illustrate and explain combined and separate sewer systems. 

Stormwater runoff occurs when rain or melting snow flows off rooftops, streets, and parking lots. Instead of being naturally absorbed into the ground, much of the stormwater in Cook County flows into combined sewers.

During heavy rainstorms, these local sewers can become overwhelmed, causing back ups that lead to flooded homes and combined sewer overflows that carry pollution into our rivers.