Combined Sewers - What's Different?

The graphics to the right illustrate the workings of typical combined sewer systems and separated sewer systems.

System structure

A combined system conveys waste water from homes along with clear water from private property, often including roof and foundation drains plus rainwater from street drains in a single pipe to the Metropolitan Milwaukee Sewerage District facilities for treatment. 

Many of Shorewood’s combined sewers date to the early 1900’s and are some of the Village’s earliest infrastructure installations. Combined sewers differ from the more modern separated sewer systems in which wastewater and rainwater are conveyed in separate pipes.  Rainwater from Shorewood’s separated system is discharged to the Milwaukee River while the wastewater is conveyed to the MMSD.

Much of a combined sewer system’s capacity is designed for managing stormwater, however long duration or intense rain events can easily overwhelm a combined sewer system causing basement back-ups.


About 60% of the geographic area of the Village of Shorewood is served by combined sewers. All combined wastewater flows to a single point of discharge to the MMSD system. This means that every improvement - every drop of water removed from the system - benefits every property in Shorewood’s combined sewer service area no matter where the improvement is physically located.

Conversely, the Village’s separated area is comprised of five sewersheds each of which have a separate point of discharge to the MMSD system. Improvements to those areas are geographically specific - a project in Basin 1 will not impact the performance of the system in Basin 6, for example.

Additional information on the Village’s sewer systems (combined, sanitary and storm) through links from the Utilities page.

Graphic credit : MMSD

Combined Sewer Diagram

Graphic credit: MMSD

Separated Sewer System Diagram