From the fund created pursuant to § 9-38-69 shall be paid as incurred and allowed all normal, reasonable, and current expenses of the operation and maintenance of the facilities, and the revenues remaining in said fund from time to time after payment of such expenses shall be appropriated to a separate account to the extent necessary for the payment of principal of and interest on the bonds and maintenance of such reserves securing said payments as shall be covenanted and agreed with the purchaser and holders of said bonds.
SDCL 9-38-72