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 on July 1, 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.
The City Council will review the 2026 Stormwater Code Update legislation in April and May where public comment will be accepted. See the Get Involved page for more detailed information and agendas.
City Council Public Meetings:
- April 9, 2026 - Governance & Utilities Committee discussion of the proposed 2026 Stormwater Code.
- May 14, 2026* - Governance & Utilities Committee anticipated vote to recommend passing the legislation.
- May 19, 2026* - Full City Council Meeting anticipated vote to adopt the proposed 2026 Stormwater Code.
* The Council will confirm the agenda prior to the meetings.
Visit our Get Involved page for more information on past public reviews and meetings.
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