Tex. Local Government Code § 375.203

(a) The board may pledge all or part of the income or assessments from improvement projects financed under this chapter or from any other source to the payment of the bonds, including the payment of principal, interest, and any other amounts required or permitted in connection with the bonds. The pledged income shall be set and collected in amounts that will be at least sufficient, with any other pledged resources, to provide for all payments of principal, interest, and any other amounts required in connection with the bonds and, to the extent required by the order or resolution authorizing the issuance of the bonds, to provide for the payment of expenses in connection with the bonds and to pay operation, maintenance, and other expenses in connection with the improvement projects authorized under this chapter.

(b) Bonds may be additionally secured by a mortgage or deed of trust on real property relating to the facilities authorized under this chapter owned or to be acquired by the district and by chattel mortgages, liens, or security interests on personal property appurtenant to that real property. The board may authorize the execution of trust indentures, mortgages, deeds of trust, or other forms of encumbrance to evidence the indebtedness.

(c) The board may pledge to the payment of the bonds all or any part of any grant, donation, revenues, or income received or to be received from the United States government or any other public or private source.