Mo. Rev. Stat. § 247.171

The proportion of the sum of all outstanding bonds and debt, with interest thereon, that is required to be paid to the water supply district, pursuant to subsection 1 of section 247.031, and subdivision (5) of subsection 1 of section 247.170, shall be the same as the proportion of the assessed valuation of the real and tangible personal property within the area sought to be detached and excluded bears to the assessed valuation of all of the real and tangible personal property within the entire area of the water supply district.