Texas Water Code - WATER § 62.198. Validity of Bonds

(a) After the bonds have been approved by the attorney general and registered by the comptroller, they shall be held in every action, suit, or proceeding in which their validity is or may be brought in question prima facie valid and binding obligations.

(b) In every action brought to enforce collection of bonds or interest on them, the certificate of the attorney general, or a duly certified copy of it, shall be admitted and received as prima facie evidence of the validity of the bonds and the coupons attached.

(c) The only defense that can be offered against the validity of the bonds or coupons is forgery or fraud.