Mo. Rev. Stat. § 577.150: Tampering with a water supply — penalty.

1. A person commits the offense of tampering with a water supply if he or she purposely:

(1) Poisons, defiles, or in any way corrupts the water of a well, spring, brook, or reservoir used for domestic or municipal purposes; or

(2) Diverts, dams up, and holds back from its natural course and flow any spring, brook, or other water supply for domestic or municipal purposes, after said water supply shall have once been taken for use by any person or persons, corporation, town, or city for their use.

2. The offense of tampering with a water supply is a class E felony when the offense is a violation of subdivision (1) of subsection 1 of this section and is a class A misdemeanor when the offense is a violation of subdivision (2) of subsection 1 of this section.