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

Walla Walla County funds its stormwater program through the Stormwater Management Utility created by WWCC 11.04.020 under RCW Chapter 36.89, which bills every developed parcel in the unincorporated county an annual service charge under WWCC 11.04.040 based on impervious surface area, with one equivalent residential unit (ERU) set at five thousand square feet under WWCC 11.04.050(A). WWCC 11.04.070 lists three credits against that charge, and subsection B is the county's rainwater harvesting credit: a new or remodeled commercial building using a properly constructed and maintained rainwater harvesting system qualifies for a credit toward the portion of the service charge attributable to that building, and county staff will consider an additional rate reduction on a case-by-case basis depending on how much rainwater the system actually harvests.

The credit is not automatic. Under WWCC 11.04.070's introductory paragraph, an owner must apply to the stormwater management utility on the county engineer's form with substantiating documentation, and the county engineer must grant the credit by October 15 of a given year for it to apply to the following year's billing; credits can carry forward across multiple years if the qualifying conditions continue to be met. A denial or dispute over the amount is final unless the owner appeals in writing within thirty days to the Board of County Commissioners under WWCC 11.01.080. The rainwater harvesting credit applies only to commercial buildings, not single-family residential parcels, which already receive the flat ERU base rate under WWCC 11.04.050(A).