Tex. Water Code § 17.891

Since the board is performing an essential governmental function in the exercise of the powers conferred on it by this chapter, the bonds issued under this subchapter and the interest and income from the bonds, including any profit made on the sale of bonds, and all fees, charges, gifts, grants, revenues, receipts, and other money received or pledged to pay or secure the payment of the bonds are free from taxation and assessments of every kind by this state and any city, county, district, authority, or other political subdivision of this state.