Working for a safe, affordable, vibrant, innovative, and interconnected city.
Learn More
Seattle.gov Home Page
Seattle.gov This Department

Drainage & Wastewater

Property owners are responsible for properly conveying all stormwater, groundwater and wastewater to an approved discharge location. Detention, treatment, or green stormwater infrastructure requirements may be imposed.

In the City of Seattle, all proposed development is checked for its impact on existing drainage and wastewater infrastructure. A Master Use, Building or Street Use Permit will not be issued until all concerns regarding drainage and wastewater have been addressed. Infrastructure improvements may be required as a condition of the permit when existing infrastructure is unavailable or inappropriate. The City and King County share jurisdiction and infrastructure in some parts of Seattle, so in some cases a permit may also be required from King County.

Drainage

Drainage refers primarily to the flow of storm water to the sea, a lake or another natural water repository, or to a combined sewer. Drainage can also include relatively clean water from other sources, such as groundwater, that needs to be managed. Seattle's Drainage Code, SMC 22.800-22.808, has been revised effective 11/30/09. The revised code has new requirements for green stormwater infrastructure when certain development thresholds are exceeded. For more information, see Drainage Code, Directors Rules, and related CAMS.

Wastewater

Wastewater refers to sewage, such as that released by toilets, bathtubs, commercial applications, or other everyday sources of contaminated water. Not all contaminated water can be disposed of as wastewater in the City or King County sewer system. Water contaminated by petroleum products, certain chemicals or bio-hazardous materials cannot be treated effectively by the County’s sewage treatment facilities, and must be pre-treated by a specialized facility, typically on site, or managed in another way.