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Revised on-site sewage system codes
King County revised the codes (rules) that govern on-site sewage systems (OSS). We did this to comply with recent changes to state law, and we used the opportunity to improve the codes and incorporate the latest best science. The new codes go into effect on April 1, 2025.
Read the new codes
The new codes aim to make it easier and cheaper to maintain, repair, and replace septic systems, as well as protect people’s health and the environment.
Code language
- Revised rule and regulation: Board of Health Title 13, On-site Sewage Systems (1.2 MB). This is the pre-final code language about OSS in King County.
More information about the code revision process
Frequently Asked Questions
No. If your septic system is functioning, no upgrades are necessary. The code changes make small changes to processes that already exist for septic system permitting and maintenance, so the only times when the new code revisions might impact an existing septic system is during a permitting or maintenance activity.
For example, one of the proposed changes is to require that all septic tank lids be secured to prevent risks of kids or pets falling into the tank. If this change goes into effect, the maintainer who next inspects your septic system would need to make sure that the lids are secured during that inspection.
No. There is no annual fee. We didn’t even consider proposing this as part of the code revisions.
No, Health Department inspectors do not go onto your property without your permission.
No, a septic system failure can be caused by many different things. If the tank or smaller parts of the septic system are broken, those can be easily and quickly fixed. The biggest failure is when the drainfield stops working. If this happens and your septic tanks are still holding water, you can use the same tanks in a new septic system replacement.
Background
In early 2024, the Washington State Department of Health approved new OSS codes. Since then, we have worked to figure out how to incorporate the state's changes into our local codes (our local codes are required by law to be at least as restrictive as the state's codes).
In early June, we launched a website and survey with proposed code revisions, in order to get public feedback. Over the course of this summer, we hosted 13 public meetings and received hundreds of comments.
In September, we released draft proposed changes to the codes for public comment. We met with and heard from hundreds of King County residents at six public comment meetings and through our public comment survey about the proposed language. We reviewed public comments and finalized the proposed revisions.
In January 2025, we presented the proposed changes to the Board of Health for their review and, in February, the Board of Health voted to adopt the proposal.
Key steps in the code revision process
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March 2024
State Board of Health finalizes revised OSS codes.
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May – October 2024
King County public engagement period - change to comment on possible local code revisions.
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January – February 2025
King County Board of Health reviews and votes on local code revisions.
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April 2025
Revised local codes go into effect.
Contact
If you need language assistance, please contact eulee@kingcounty.gov
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Amharic: የቋንቋ እርዳታ ከፈለጉ፣ እባክዎን በ eulee@kingcounty.gov ያግኙን