Tex. Water Code § 15.432

(a) The state water implementation fund for Texas is a special fund in the state treasury outside the general revenue fund to be used by the board, without further legislative appropriation, for the purpose of implementing the state water plan as provided by this subchapter. The board may establish separate accounts in the fund. The fund and the fund's accounts are kept and held by the trust company for and in the name of the board. The board has legal title to money and investments in the fund until money is disbursed from the fund as provided by this subchapter and board rules. It is the intent of the legislature that the fund will never be used:

(1) for a purpose other than the support of projects in the state water plan; or

(2) to certify that appropriations from the treasury are within the amount estimated to be available in a fund of the treasury affected by the appropriation.

(b) Money deposited to the credit of the fund may be used only as provided by this subchapter.

(c) The fund consists of:

(1) money transferred or deposited to the credit of the fund by law, including money from any source transferred or deposited to the credit of the fund at the board's discretion as authorized by law;

(2) the proceeds of any fee or tax imposed by this state that by statute is dedicated for deposit to the credit of the fund;

(3) any other revenue that the legislature by statute dedicates for deposit to the credit of the fund;

(4) investment earnings and interest earned on amounts credited to the fund; and

(5) money transferred to the fund under a bond enhancement agreement from another fund or account to which money from the fund was transferred under a bond enhancement agreement, as authorized by Section 15.435.