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 and comment periods and public meetings during three separate timeframes: 

• Summer 2025:
  • First public review draft comment period is July 8-August 8, 2025. Documents are available on the Project Documents page.
  • Virtual public meeting will be held on July 15, 1 - 3 PM. Registration is required. See the Get Involved page for more information.
• Fall 2025 / Winter of 2026: Second public review draft comment period.
• Spring 2026: City Council public meeting. 

We will continue to update this website with public meeting schedule information as it becomes available. 

For more information on how to participate in the public meetings and comment, see 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 (SMMWW), 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