Tex. Auxiliary Water Laws § 7857

Two or more districts may by contract join in the construction of any improvement and enter upon any work authorized hereunder, as a joint project, when in the judgment of the directors of each district, such improvement, work or construction will be advantageous to the respective districts. Such contract shall stipulate the pro rata amount to be paid by each district for such project to provide for its maintenance, repair and reconstruction, and shall be executed by the directors. Such project may be undertaken regardless of the location of the proposed work. Such contract may be enforced and specific performance compelled by any court of competent jurisdiction.