Mo. Rev. Stat. § 91.100: May contract to supply.

Any such city which shall erect or acquire a system of waterworks under sections 91.090 to 91.300 may, and is hereby authorized and empowered to, supply water from its waterworks to persons and private corporations for use in or beyond the corporate limits of the city, and to enter into any such contracts therefor, upon such terms and under such rules and regulations as may be agreed upon by the contracting parties.