Snohomish County, WA Landscaping Rules: Rainwater Harvesting (2026)

040 as a system for storing, collecting, and reusing rainwater from a rooftop at a commercial-use building that has been designed and constructed in accordance with the Washington State Building Code Council's Permissive Rainwater Harvesting System Guidelines for Non-residential Occupancies, has a storage volume of at least 10 percent of the mean annual runoff volume generated from the contributing roof area, and has been approved by the director of the department of planning and development services. 070(4), part of the surface and storm water management utility's rate structure, provides that the rate charged for real property with a commercial rainwater harvesting system shall be reduced from the rate set out in this chapter by a fraction equal to the storage volume of the rainwater harvesting system divided by the mean annual runoff volume generated by the total impervious surface area of the property.

In practice, the bigger the system relative to the roof's total annual runoff, the bigger the proportional cut to the property's annual surface water management service charge. 080(2) for properties holding an active NPDES discharge permit. 132's commercial-development definition; there is no equivalent credit written into the code for a residential rain barrel or cistern.