Mo. Rev. Stat. § 184.366

Before incurring any indebtedness under the provisions herein the board of said district is hereby authorized and shall provide for the collection of an annual tax on all taxable tangible property therein sufficient to pay the interest and principal of the indebtedness as they fall due and to retire the same within twenty years from the date contracted. The said tax levy shall be in addition to that tax levy authorized by the voters as provided in section 184.350.