Average single-family homes, duplexes and triplexes are charged a flat fee per unit per year. Other properties are charged based on the amount of hard surface (rooftop, parking lot, gravel, storage lot, areas where the natural vegetation has been disturbed for parking, driving, etc.) on the property.
Annual stormwater rates are based on an Equivalent Residential Unit (ERU) measurement. Parcels with the drainage characteristics of a single-family parcel receive a flat rate. The average single-family residential parcel in unincorporated Spokane County has 3,160 square feet of hard (impervious) surfaces. This is defined as 1 ERU. The rate for 1 ERU is determined by the service area, as described below.
Stormwater service charges for businesses, industries, farms, apartment buildings and other non-residential land uses are calculated based on their impervious coverage as compared to the average single-family residential unit. For example, if a commercial parcel has four times more impervious coverage than a residential parcel, it is charged four times the single-family rate for the drainage service area.
Annual charges are based on the specific rates for each of the service areas as shown below. Maps of the specific service areas are available from Spokane County Engineering and Roads, Stormwater Section.