The City of Columbus has a complex sewer system made up of three types of sewers:

• Combined Sewers - these carry both sewage and rain water to treatment plants, where both are treated then released into a river

• Separate Sewers - these are separated sanitary (for sewage) and storm sewers

• Storm Sewers - located on curbs or in drainage ditches, these sewers empty rain water (and anything carried with it) directly back into rivers.

Many cities, including Columbus, are experiencing issues with their combined and separated sanitary sewer systems, because they are often overloaded during heavy rain events. This causes combined sewers to overflow into rivers (see image below), which causes public health and ecological problems.