How to Get the Green Stormwater Infrastructure (GSI) Mini Grants Rebate

What you get

Pays landowners in the King County Wastewater Treatment Division service area who are not eligible for other incentive programs, such as RainWise, for a completed rain garden, cistern, depave project, green roof or Grattix box. The award is the contributing area (the square footage where rainfall is captured) times a rate, and never more than the project cost. Rates on the application: rain garden $4 per sq ft ($6 income-limited), depave $4 per sq ft of area depaved ($6), cistern draining to landscape $1.50 per sq ft ($3.50), cistern draining to side sewer $0.75 per sq ft ($2.25), green roof $1.25 per sq ft ($3.50), Grattix $1.50 per sq ft ($3.50). Payment is issued after the project is completed. Optional pre-approval holds funds for up to 3 months. Check your address on the King County WaterWorks eligibility map before applying; the cities listed here send wastewater to King County, and the service area boundary does not follow city limits exactly (Stewardship Partners, GSI Mini Grants page and application dated July 2026; last verified October 2026).

• Residential: $4 per sq ft of contributing area for a rain garden, not more than project cost ($6 per sq ft income-limited)

Are you eligible?

• Be a Stewardship Partners (King County Wastewater Treatment WaterWorks Grant Program) customer
• Property inside the King County Wastewater Treatment Division service area (check the WaterWorks eligibility map)
• Project is not eligible for other incentive programs, such as RainWise
• Legal ownership of the property, with documentation
• Maintain the feature for at least five years
• Rain gardens follow the Rain Garden Handbook for Western Washington, with no more than 2,000 sq ft draining to a single rain garden unless local drainage codes are met
• Application with award calculation, project budget, site sketch, expense receipts, and photos of the installed project
• Income documentation if applying as income-limited