Preventing Sewer Overflows and Problems

No one wants their sewage back! SPU works to maintain, build and manage Seattle's sewer system to protect our city and the environment from overflows and backups.

To do this, SPU:

Combined Sewer Overflows (CSOs) are one type of sewer overflow.

In some parts of the City, our sewage and stormwater flows together in a single set of pipes. In these areas, heavy rains can cause sewer overflows into our waterways at known relief points. These overflows are called “combined sewer overflows” or CSOs. CSOs create significant health and environmental risks. SPU is investing in major projects, like the Ship Canal Water Quality Project, to reduce these overflows.