Sewer & Drainage

For certain development projects, property owners and developers must properly convey the following to an approved location:

You may need to make infrastructure improvements when existing infrastructure is unavailable or inadequate.



Drainage is stormwater and groundwater. It must be properly managed to avoid damage to people, property, or the environment.

The Stormwater Code and Manual has requirements for onsite stormwater management when certain development thresholds are exceeded.



Wastewater is sewage. Examples include water from toilets, bathtubs, or other sources of contaminated water.

Not all contaminated water can be disposed of as wastewater in Seattle’s or King County’s sewer systems. See the Side Sewer Code for requirements.

You can also research water availability with our water and sewer map.