Supplemental to any existing law on the subject and in lieu of the issuance of general obligation bonds, or the levying of taxes upon property, as by law provided, any city of the second class or any village may construct, purchase, or otherwise acquire a waterworks plant or a water system, or a gas plant or a gas system, including a natural or bottled gas plant, gas distribution system, or gas pipelines, either within or without the corporate limits of the city or village, and real and personal property needed or useful in connection therewith, and pay the cost thereof by pledging and hypothecating the revenue and earnings of any waterworks plant or water system, or gas plant or gas system, including a natural or bottled gas plant, gas distribution system, or gas pipelines, owned or to be owned by the city or village. In the exercise of the authority granted in this section, the city or village may issue and sell revenue bonds or debentures and enter into such contracts in connection therewith as may be proper and necessary. Such revenue bonds or debentures shall be a lien only upon the revenue and earnings of the waterworks plant or water system, gas plant or gas system, including a natural or bottled gas plant, gas distribution system, or gas pipelines, owned or to be owned by the city or village. No such city or village shall pledge or hypothecate the revenue and earnings of any waterworks plant or water system, or gas plant or gas system, including a natural or bottled gas plant, gas distribution system or gas pipelines, nor issue revenue bonds or debentures, as authorized in this section, until the proposition relating thereto has been submitted in the usual manner to the qualified voters of such city or village at a general or special election and approved by a majority of the electors voting on the proposition submitted. Such proposition shall be submitted, whenever requested, within thirty days after a sufficient petition signed by the qualified voters of such city or village equal in number to twenty percent of the vote cast at the last general municipal election held in such city or village is filed with the city clerk or village clerk, as the case may be. Three weeks' notice of the submission of the proposition shall be given by publication in a legal newspaper in or of general circulation in such city or village. The requirement for a vote of the electors shall not apply when such city or village seeks to pledge or hypothecate such revenue or earnings or issue revenue bonds or debentures solely for the maintenance, extension, or enlargement of any waterworks plant or water system, or any gas plant or any gas system, including a natural or bottled gas plant, a gas distribution system, or gas pipelines, owned by such city or village.