For questions about the Wastewater Treatment Division website, please send an e-mail message or contact us at:

King Street Center
201 S. Jackson St., Suite 500
Seattle, WA 98104-3855
Phone: 206-684-1280
Fax: 206-684-1741
Telecommunication device for the deaf (TTY): 711

Get Directions to our office location in Seattle, Washington.

Staff Contacts
Puget Sound shoreline next to the West Point Treatment Plant, Seattle

King County's Wastewater treatment process

The process used at our two regional treatment plants provides secondary treatment (preliminary, primary and secondary treatment, and disinfection). The image below shows the basic steps in the treatment process. Move your mouse over the image and click on the "hot links" to view more information about programs and processes.

Note: Stormdrains are connected to the sewer system only in the combined sewer system in parts of Seattle.

Treatment process

Besides our principal work of treating wastewater, we provide odor control, investigate and assess new wastewater treatment technologies, and strive to be a good neighbor during construction.

To find out more about King County's wastewater system:

King County provides wholesale wastewater treatment services to local sewer agencies. The local agencies own and operate independent collection systems, which include pipelines and pump stations to collect and carry wastewater flows in their service area to King County's regional system for treatment and disposal.Regional sewer pipes and pump facilitiesKing County discharges treated wastewater under permits issued by the Washington State Department of Ecology (Ecology). Ecology administers the National Pollutant Discharge Elimination System (NPDES) permits under authority delegated to the department by the U.S. Environmental Protection Agency.Combined sewer overflow statusIndustrial Waste ProgramLet's talk trash. Water quality starts with each of us.Energy recoveryBiosolids recyclingReclaimed waterLearn more about resource recoveryAdvanced treatmentTo learn about the wastewater treatment process, view the links on right-hand side of page.

Learn more about wastewater treatment

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Take an animated tour of the treatment process at South Plant. More about the South Plant treatment process.

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Take an animated tour of the liquid treatment process at West Point. More about the West Point treatment process.

Visit "Be in the Know ...Go with the Flow" -- an interactive online map that allows the water curious to walk through the wastewater treatment process. Presented by the Water Environmental Federation.

WEF animation