Each corporation organized under this article or the articles of incorporation of which are amended under this article may, if it so elects, combine and consolidate any of its systems (whether water, sewer, gas, or electric) with any one or more of its other systems (whether water, sewer, gas, or electric) and provide for the operation, maintenance, and repair of the systems so consolidated as one combined and consolidated system, the keeping of books and records for one combined system and the borrowing of money for any purpose authorized by law and the issuance of revenue bonds payable from the revenues of the combined system, or such corporation may keep and operate any one or all of its systems separate from its other systems. One combination and consolidation of systems shall not prevent other combinations and consolidations of other systems or the combination and consolidation of another system or systems with said consolidated system.