(a) Where bonds are payable wholly from revenues, the governing body shall fix and from time to time revise the rates, tolls, and charges from the sales and services rendered by the district, the revenues from which are pledged, to the end that the rates, tolls, and charges will yield sufficient money:
(1) to pay designated expenses of the district;
(2) to pay the principal of and interest on the bonds as the principal and interest mature; and
(3) to create and maintain funds as prescribed in the resolution authorizing or the trust indenture securing the bonds.
(b) Where the bonds are payable both from taxes and from revenues, the governing body shall fix and from time to time revise the rates, tolls, and charges for sales and services rendered by the district, to the extent pledged, which will be sufficient to assure compliance with the resolution authorizing the bonds or the trust indenture securing them.
Official text of the Texas Water Code as published by the Texas Legislative Council.