Skip to main content
King County Courthouse Third Avenue entrance closed until January 1, 2020. Please use alternative routes.  
King County logo

The process used at our three regional treatment plants provides secondary treatment (preliminary, primary and secondary treatment, and disinfection).

The graphic below shows the basic steps in the treatment process.

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

2016_RR-treatment-process_1000Source: Ratepayer Reportpages 4 and 5 

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:

Learn more about wastewater treatment

Visit the wastewater education and tours site to learn about our programs, education resources and events, and how you can help the environment.