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King County protects water quality and public health in the central Puget Sound region by providing high quality and effective treatment to wastewater collected from our local sewer agencies.

The county's Wastewater Treatment Division (WTD) serves about 1.8 million people within a 424-square-mile service area, which includes most urban areas of King County and parts of south Snohomish County and northeast Pierce County.

King County's wastewater system includes:

Service area and treatment plants

Map of service area and facilities