Mo. Rev. Stat. § 204.410: Net revenues defined, how expended.

1. Whenever any common sewer district authorizes and issues revenue bonds pursuant to sections 204.250 to 204.470, an amount sufficient for the purpose of the net revenues of the sewerage system for the benefit of which the bonds are issued shall, by operation of sections 204.250 to 204.470, be pledged to the payment of the principal of and the interest on the bonds as the same shall mature and accrue.

2. The term "net revenues" shall be construed to mean all income and revenues derived from the ownership and operation of the system less the actual and necessary expenses of operation and maintenance of the system.

3. It shall be the mandatory duty of the treasurer of the common sewer district to provide for the prompt payment of the principal and interest on any revenue bonds as they mature and accrue.