(1) A utility that is required to have a tariff on file with the commission must file and maintain its tariff(s) as required in the RCW and WAC.

(2)(a) A utility that provides more than one kind of service, such as gas, electric, or water, must file a separate tariff for each service type.

(b) Each tariff must have an official designation number, printed as WN U-number. Subsequent tariff designations must be sequentially numbered in ascending order.