Tex. Water Code § 53.185: RATES AND CHARGES.

If the board issues revenue bonds or combination tax and revenue bonds, the board, at the time it authorizes the bonds, shall fix rates and charges for the use of the facilities or the services rendered in an amount which, together with any tax which is levied, will assure the prompt payment of the principal of and interest on the bonds as they mature.

Acts 1971, 62nd Leg., p. 417, ch. 58, Sec. 1, eff. Aug. 30, 1971.