(a) When bonds have been approved, the commissioners court annually shall levy and have assessed and collected improvement taxes sufficient to pay the interest on the bonds and to provide a sinking fund to redeem the bonds at maturity.
(b) The commissioners court shall also at the time of the levy of taxes for county purposes, levy and have assessed and collected for the maintenance, operation, and upkeep of the district and its improvements an annual tax of not more than 10 cents on each $100 valuation.
(c) The commission shall determine a rate within the 10-cent limit as the necessary amount for the maintenance, operation, and upkeep of the district and its improvements. The rate shall be certified to the commissioners court by the commission.
(d) Taxes shall be levied on all property inside the district.