Section 250.120 - Revenue bonds - rates charged to be sufficient to pay principal and interest1. It shall be the mandatory duty of any city, town or village or sewer district which shall issue revenue bonds pursuant to this chapter to fix and maintain rates and make and collect charges for the use and services of the system for the benefit of which such revenue bonds were issued, sufficient to pay the cost of maintenance and operation thereof, to pay the principal of and the interest on all revenue bonds or other obligations issued or incurred by such city, town or village or sewer district chargeable to the revenues of such system and to provide funds ample to meet all valid and reasonable requirements of the ordinance or resolution by which such revenue bonds have been issued. Such rates shall be from time to time revised so as fully to meet the requirements of this chapter. As long as any bond so issued or the interest thereon shall remain outstanding and unpaid, rates and charges sufficient to meet the requirements of this section shall be maintained and collected by the city, town or village or sewer district which shall have issued such bonds.2. Such rates shall be fixed and charged regardless of whether or not the services of the system shall previously have been rendered without charge therefor by the previously existing waterworks system, sewerage system or combined waterworks and sewerage system and regardless of how the acquisition of such system shall have been financed, whether by taxation, special assessment, the issuance of bonds or otherwise.3. If the system shall be a combined waterworks and sewerage system, rates and charges may be established, fixed and collected for water services only, for sewer services only or for both services combined and, in such case, the city, town or village shall be and is hereby authorized to discontinue water service upon any failure to pay within a reasonable time the charges fixed for either water service or sewer service or for both services combined.4. It shall be lawful for any such city, town or village or sewer district to base its sewerage rates in whole or in part upon the amount of water supplied to the premises charged for sewerage services by any private water company; in such case it shall be the duty of such private water company to furnish to such city, town or village or sewer district such information as is necessary to calculate its charges for sewerage service.