Separated sewer system

In separated sewer systems, sanitary sewers convey wastewater from homes and businesses to treatment plants in different pipes than those that carry stormwater to drainage outlets. Approximately 27% of Seattle’s wastewater system is separated (mostly in the north end).

This infographic shows how a separated sewer system works under a home. Rainwater flows from the roof into gutters and storm drains, then travels through a pipe that carries stormwater directly to a nearby water body, such as a river or the ocean. Wastewater from sinks and toilets flows through a separate pipe to a treatment plant, where it is cleaned before being released.