Mo. Rev. Stat. § 631.105

If an adult person for himself, a parent for a minor, or a guardian for a ward applies to the head of a public or private alcohol or drug abuse facility to receive treatment and rehabilitation, and if the head of the facility believes that the person engages in alcohol or drug abuse, or both, and would benefit from the program offered by the facility and that suitable accommodations are available, he may admit the person for treatment and rehabilitation as a voluntary client. A minor may apply for himself if competent to do so under section 431.061.