Mo. Rev. Stat. § 91.090: Certain cities may construct or acquire waterworks.

The city council of any city of the third or fourth class in this state, or any city operating under a special charter, having three thousand inhabitants or more and less than one hundred and fifty thousand inhabitants shall have the power to erect, maintain and operate waterworks or to acquire waterworks by purchase as herein provided, and to operate and maintain the same and supply the inhabitants thereof with water and to charge therefor reasonable rates as herein provided.