Mo. Rev. Stat. § 249.805

For the purpose of refunding, extending or unifying the whole or any part of any outstanding revenue bonds of the district, any district may issue its refunding revenue bonds not exceeding in amount the principal of the outstanding revenue bonds to be refunded, together with the accrued interest to the date of the refunding bonds, and the board of the district shall provide for the payment of the interest on and principal of the refunding bonds in the same manner and from the same source as was provided for the payment of interest on and principal of the bonds to be refunded.