Idaho Code § 50-1023: Joint services — Agreement on apportionment.

Whenever two (2) or more cities desire jointly to construct water, power or sewage systems, it shall be necessary for the councils to agree among themselves as to the kind and character of construction of the said plant and system, the amount of service to which each city shall be entitled, the approximate cost of such systems and the proportionate part thereof which shall be borne by each city, which proportionate part shall be as nearly just and equitable as possible, and shall be determined in such manner as may be agreeable to all concerned.