65 ILCS 5/11-128-7

The corporate authorities from time to time shall fix the water rentals or rates to be charged for the furnishing of water. These rentals or rates shall be made sufficient, together with the proceeds of the special tax provided in this Division 128, to pay at maturity the interest and principal of bonds issued under the provisions of this article, and also for the proper maintenance and operation of the waterworks, and for all repairs thereon.