Tex. Water Aux. Laws § 7879

There is hereby created an "Interest and Sinking Fund" for such district, and all taxes collected under this chapter for the payment of bonds and interest thereon shall be credited to such fund and shall never be paid out except for the purpose of satisfying and discharging the interest on said bonds, or for the payment, cancellation and surrender of said bonds. At the time of such payment, the depository shall receive and cancel any interest coupon so paid or any bond so satisfied or discharged, and when such coupon or bond shall be turned over to the directors, the account of such depository shall be credited with the amount thereof, and such coupon or bond shall be cancelled and destroyed.