For the purpose of making partial payments as the work progresses, warrants may be issued by the county board upon certificates of the engineer in charge showing the amount of work completed and materials necessarily purchased and delivered for the orderly and proper continuation of the project in a total amount not to exceed ninety-five percent of the cost. Upon completion and acceptance of the work, the county board shall issue a final warrant for the balance of the amount due the contractor. The county shall pay to the contractor interest at the rate of seven percent per annum on the amounts due on partial and final payments beginning forty-five days after the certification of the amounts due by the engineer in charge and approval of the county board and running until the date that the warrant is tendered to the contractor. The warrants shall be redeemed and paid out of the proceeds received from the sewer tax levy levied pursuant to section 23-3616 or usage fees adopted pursuant to section 23-3618 or out of the proceeds of the bonds or warrants issued. The warrants shall draw interest as provided in the warrants from the date of registration until paid.