The classes of service shall be residential or commercial. Residential services shall consist of all services where sewer service is supplied for domestic purposes to a single-family dwelling unit. Commercial services shall consist of all services where sewer service is supplied for a commercial or business establishment, or multidwelling units. If sewer service is supplied to a customer for use in both a single or a multidwelling unit and a commercial or business establishment, or a multidwelling unit, the rate for commercial services shall apply for the combined usage. [Prior code § 11.12.030(4).]