65 ILCS 5/11-139-4
Whenever an existing waterworks or sewerage system is included in a combined waterworks and sewerage system under this Division 139 and there are unpaid obligations previously issued, which are payable solely from the revenue or secured by a mortgage of the waterworks or sewerage system, or any part thereof, or whenever there are unpaid obligations previously issued which are payable solely from the revenue of the combined waterworks and sewerage system, the unpaid obligations may be refunded by the issue and exchange therefor of revenue bonds, to be issued under this Division 139, with the consent of the respective holders of the unpaid obligations. The holders of revenue bonds issued under this Division 139, whether (1) for refunding or (2) for acquisition, construction, extension, or improvement, or both, have the same rights and privileges with respect to payment and there is no distinction between revenue bonds issued for the 2 purposes unless it is specifically provided in the ordinance authorizing the issuance of bonds that the bonds, or such ones thereof as may be specified, issued for such acquisition, construction, extension or improvement, shall, to the extent and in the manner prescribed, be subordinated and be junior in standing, with respect to the payment of principal and interest and the security thereof, to such other bonds payable from the revenue of the combined waterworks and sewerage system as are specified in such ordinance. Whenever any unpaid obligations previously issued which are payable solely from the revenue or secured by a mortgage of any waterworks or sewerage system included in a combined waterworks and sewerage system or any combined waterworks and sewerage system under this Division 139 are refunded, the unpaid obligations shall be surrendered and exchanged for revenue bonds of the combined waterworks and sewerage system of a total principal amount which shall not be more but may be less than the principal amount of the obligations exchanged and the interest thereon to the date of exchange.
65 ILCS 5/11-139-4