When any municipal corporation has issued certificates of indebtedness hereunder and has pledged the revenues of any utility for the payment thereof, the municipality shall impose and collect fees and charges for the products, commodities, and services performed by the utility, in amounts and at rates fully sufficient at all times to
(1) pay the expenses of operating and maintaining the utility;(2) provide a sinking fund sufficient to insure the prompt payment of the certificates of indebtedness and interest thereon as they fall due;(3) provide such reasonable funds for contingencies as may be required; and(4) provide an adequate depreciation fund for repairs, extensions, and improvements to the utility necessary to insure adequate and sufficient service to the public. There shall be no charge for services to the municipality itself or to its agencies and departments. The governing authority of the municipality or any duly appointed or qualified receiver shall have the exclusive authority to fix or supervise the making of these fees and charges.