Mo. Rev. Stat. § 250.100

Any such city, town or village shall have the power, subject to a favorable vote at an election called and held as herein provided, to issue revenue bonds for the improvement or extension or both of its existing waterworks or its existing sewerage system or its existing combined waterworks and sewerage system for the purpose of serving a particular locality, and such revenue bonds may be payable from the revenues derived or to be derived from the operation of the entire waterworks or sewerage system of the city, town or village or the entire combined waterworks and sewerage system or may be payable from the revenues to be derived from the operation of the waterworks, sewerage system or combined waterworks and sewerage system in such particular locality, as may be set forth in the proposition submitted at said election, provided, however, that the pledge of such revenues shall be subject to any prior pledge thereof.