Section 42.05.471 - Depreciation rates and accounts(a) To provide for the loss in service value of its property, not restored by current maintenance, a utility shall charge adequate, but not excessive, depreciation expense for each major class of utility property used and useful in serving the public. From time to time the commission shall determine the proper and adequate rates of depreciation for each major class of property of a public utility. The commission shall accept rates of depreciation and depreciation accounts prescribed and maintained under regulations of a federal agency or the terms of a bond ordinance. The commission shall determine and allow depreciation expense in fixing the rates, tolls, and charges to be paid for the services of a public utility.(b) The commission is not bound in rate proceedings to accept, as just and reasonable for rate-making purposes, estimates of annual or accrued depreciation established under the provisions of this section, or to allow annual or accrued depreciation on utility property directly or indirectly contributed by customers or others.