Stormwater Code and Manual Update 2026 - What & Why

What's Happening Now? 

Our proposed 2026 Stormwater Code and Manual update is scheduled to be effective in July 2026. Our new rules will replace the current Stormwater code and Directors' Rules, which are administered jointly by us and Seattle Public Utilities. For more information, visit our Background page. 

As part of this process, we will be holding public review/comment periods and public meetings during three separate timeframes: 

• Summer 2025 – 1st draft (Public Review and Comment Period from July 8 – August 5, 2025. Public Meeting on July 15, 2025.)
• Winter of 2026 – 2nd draft after Ecology and public review comments are addressed. 
• Spring 2026 – City Council public meeting. 

This website will be updated with the public meeting schedule information when available.  

As they become available, we will post the documents to the site. 

There is more information on how to comment on our Get Involved page. 

Project Benefits

Our stormwater code protects people, property, and the environment by controlling how rainwater runs off streets, buildings, and parking lots. Stormwater runoff can cause flooding, landslides, and erosion that can damage our homes, businesses, and property. Stormwater runoff carries oil and grease, fertilizers, pesticides and other toxic chemicals to our creeks, lakes, bays, rivers, and other waterways.

The End Result

Our regulations will be equivalent to 2024 Stormwater Management Manual for Western Washington, as required by our Ecology NPDES Phase 1 Stormwater Municipal Permit (NPDES Permit), and will address the following topics: 

• Required Equivalency Items as identified by Ecology (Appendix 10 of the NPDES Permit)
• General clarifications to improve usability
• Improve stormwater management for new development in Seattle
• Improve the Construction Site Stormwater Runoff Controls requirements
• Clarify Pollution Prevention, Good Housekeeping, and Operation and Maintenance
• Updates to Flow Control, Water Quality Treatment, and Source Control Practices