The existing sewerage system of its entirety, together with all additions, improvements and extensions thereto that may hereafter be made shall be maintained and operated as a single utility and a charge or rate shall be established for the use of the said sewerage system, which shall be reasonable and commensurate with the services performed by the sewerage system, and shall be sufficient to maintain, operate, provide an adequate depreciation fund and pay the principal and interest on any revenue bond which may be issued which by their terms are made payable from the revenues of the said sewer system. (Ord. 688, 2-20-1989)