The rates and charges established for the services and facilities afforded by this system must be sufficient in each year to provide income and revenue adequate for the:
(1) payment of the reasonable expense of operation and maintenance;
(2) payment of the sums required to be paid into the sinking fund;
(3) accumulation of reserves;
(4) payment of rates, fees, and charges levied by a regional authority established pursuant to Title 75, chapter 6, part 3; and
(5) payment of expenditures for depreciation and replacement of the system as determined necessary by the governing body or as covenanted in the ordinances and resolutions authorizing the outstanding bonds.