Mo. Rev. Stat. § 91.060

Any city, town or village in this state having authority to maintain and operate waterworks may procure water for that purpose from any other city having a system of waterworks, and to that end may enter into a contract therefor with such city having a system of waterworks; and any city of this state having a waterworks system is hereby authorized and empowered whenever it deems it expedient to supply any other city, town or village of this state in its vicinity with water from its waterworks for such time and upon such terms and under such rules and regulations as it may deem proper.