(a) In this section, “fee” includes any fee, charge, or toll.
(b) The necessary and reasonable expenses of operation and maintenance of the properties and facilities whose revenues are pledged to the payment of the revenue bonds are a first lien on and charge against the income of the properties and facilities. While any of the bonds or interest remains outstanding, the board shall charge and require the payment of fees for the use of the properties and facilities. The board shall determine the rates of fees charged by it for the use, operation, or lease of the properties and facilities. Fees must be equal and uniform within classes and must be in amounts that yield revenues at all times at least sufficient to pay the expenses of operation and maintenance, and to provide for the payments prescribed in the bond order for the establishment and maintenance of the funds provided for in the bond order, including the interest and sinking fund and each reserve fund. The bond order may make additional covenants with respect to the bonds and the pledged revenues and the operation, maintenance, and upkeep of those properties and facilities, the income of which is pledged.

(c) The commissioners court shall ensure that the fees charged by the board are sufficient to comply with this subchapter. If for any reason the fees are not sufficient, the commissioners court shall impose additional fees so that the revenue will be sufficient.
(d) If any part of the security for the bonds consists of money to be received by the board as consideration for properties or facilities belonging to the county but operated by a person other than the board under a lease or operating contract, the board shall fix and authorize fees to be charged by the person for services rendered by the properties or facilities. The fees must be in amounts at least sufficient to assure receipt by the board of money that the board is committed to pay from that source for the benefit of the revenue bonds under the bond order.