Unless modified under Subchapter J, Chapter 49, Water Code, or other law, the authority's territory is composed of:
(1) all of Jefferson, Hardin, and Tyler Counties;
(2) a strip of land 10 miles in width off the eastern end of Liberty County (the west line of that strip being parallel to and 10 miles west of the extreme eastern boundary line of Liberty County); and
(3) a strip of land 15 miles in width off the east side of Chambers County (the west line of that strip being parallel to and 15 miles west of the eastern boundary line of Chambers County).