Mo. Rev. Stat. § 71.540
It shall be lawful for any incorporated city, town or village in this state to enter into a contract separately or in conjunction with any other incorporated city, town or village, or cities, towns or villages, or with any private corporation or corporations, or with any corporation now or hereafter engaged in pumping and delivering water at wholesale for domestic consumption. It shall also be lawful for any such incorporated city, town or village, or cities, towns and villages in this state to acquire, own and hold, separately or in conjunction with any other city, town or village, or cities, towns or villages, or any private corporation in this state, water mains or interests in water mains through which to procure an adequate supply of water for its inhabitants.
§ 71.540, RSMo