Idaho Code § 50-1022

In addition to the authority contained in the foregoing sections and in sections 67-2326 through and including 67-2333, Idaho Code, it shall be lawful for two (2) or more cities, so situated with reference to each other that it is practicable and convenient to furnish the said inhabitants thereof with water, power or sewerage from a single plant and system, to join in the construction or purchase of such plant or system upon a substantial compliance with the provisions of sections 50-1022 to 50-1025, Idaho Code, and not otherwise.