Tex. Water Code § 30.031

(a) When all or part of the payments under a contract are to be made from revenue of the waterworks system, sanitary sewer system, both systems, or a combination of both systems, the public agency shall establish, maintain, and periodically adjust the rates charged for services of the systems, so that the revenue, along with any taxes levied in support of the indebtedness, will be sufficient to pay:

(1) the expenses of operating and maintaining the systems;

(2) the obligations to the district under the contract; and

(3) the obligations of bonds that are secured by revenue of the systems.

(b) The contract may require the use of consulting engineers and financial experts to advise the public agency on the need for adjusting rates.

(c) Notwithstanding any provision of this chapter or any other law to the contrary, a district may use the proceeds of bonds issued for the purpose of constructing a waste disposal system or systems, and payable wholly or in part from ad valorem taxes, for the purchase of capacity in, or a right to have the wastes of the district treated in, a waste collection, treatment, or disposal system and facilities owned or to be owned exclusively or in part by another public agency, and a district may issue bonds payable wholly or in part from ad valorem taxes specifically for such purpose if a majority of the resident electors of the district have authorized the governing body of the district to issue bonds for that purpose or for the purpose of constructing a waste disposal system or systems. The bonds shall be issued in accordance with the provisions of, and shall be subject to the same terms and conditions of, the laws authorizing the district to issue bonds for the purpose of constructing waste collection, treatment, and disposal systems, except as otherwise provided in this subsection.