Mo. Rev. Stat. § 341.060: Plumbing regulated by city.

Each city with a population of fifteen thousand or more in the state shall, by ordinance, within three months after the passage of sections 341.010 to 341.080, prescribe rules and regulations for the material, construction and inspection of all plumbing and sewerage placed in, or in connection with, any building in each city, and the board of health or proper authorities shall further provide that no plumbing work shall be done without a permit being issued therefor upon such terms and conditions as said city shall prescribe.