A sewer that carries both sewage and stormwater runoff.
Pipes that carry both storm water and household sewage to sewage treatment plants. During a big storm, they may overflow and dump untreated sewage into streams, lakes and coastal waters. These overflows are called combined sewer overflows or CSOs.
A sewer system in which the storm water and sanitary waste are combined. The system can be overwhelmed during severe storms, resulting in untreated waste being flushed into the receiving waters as a combined sewer overflow (CSO).