Tex. Water Code § 30.026

Each river authority may make contracts authorized by this chapter with any person, including any public agency situated wholly or partly inside its boundaries and any public agency situated wholly or partly inside the river basin and any public agency situated wholly or partly inside the coastal basins adjoining its boundaries, but a river authority may not make contracts to serve a public agency situated wholly inside the boundaries of another river authority or to serve facilities of a person situated wholly within the boundaries of another river authority, except with the consent of the other river authority.