Tex. Water Aux. Laws § 7808

One or more water control and preservation districts may be established in the several counties, or a part of any county, or in two or more adjacent counties, or in parts of two or more adjacent counties, or in one county and part of an adjacent county or counties, in the manner provided in this chapter. Said districts may or may not include within their boundaries villages, towns and municipal corporations, or any part thereof, but no land shall be at the same time included within more than one such district. All such districts are defined districts within the meaning of Section 52, Article 3 of the State Constitution.