Skip to main content
Many King County facilities are closed to the public. Learn how to access services remotely or while following social distancing guidelines.  
King County logo
On-site Sewage System (OSS) Program

On-site Sewage System (OSS) Program


The Public Health On-site Sewage System (OSS) Program helps to ensure that over 85,000 septic systems including 192 septic systems in Seattle are safe. Septic systems treat wastewater when homes and buildings are not connected to public sewer systems. The OSS Program provides educational, advisory and permitting services for owners of septic systems and certifications for several septic professionals.
Think Before You Flush

Think Before You Flush

During this time when many are staying at home, it is important to keep a careful eye on actions that may affect your sewer or septic system.

Download flyers to learn more:

Septics 101 — Learn the basics

Current focus areas:

Healthy Beach Project

Healthy Beach Project

Public Health continues to work with Vashon-Maury Island residents to document improvements to water quality, find sources of excessive bacteria, and, where possible, eliminate these sources. During the 2018-2020 Pollution Identification and Correction Project, we are sampling water quality, performing visual surveys, and providing technical support and education.

Marine Recovery Area

Marine Recovery Area

A Marine Recovery Area (MRA) was established to protect especially sensitive marine waters from pollution from poorly functioning or failing on-site sewage systems (OSS). A 2006 state law (RCW 70.118A) required Puget Sound counties (including King County) to designate MRAs where shellfish growing areas are closed due to bacterial pollution (or if closure is likely), or where bacteria or nitrogen are seriously affecting water quality.

Environmental Health Services
14350 SE Eastgate Way
Bellevue, WA 98007

Phone: 206-477-8050 (answered until 3:00 pm)

Fax: 206-296-9792

Office hours:

  • Mon. Wed. Fri: 8:00 am to 3:00 pm
  • Tues. and Thurs: 10:30 am to 3:00 pm

Link/share our site at www.kingcounty.gov/oss