For purposes of this Article, the term "unit" means any of the following entities created pursuant to this Chapter:
(1) A water and sewer authority created pursuant to Article 1.
(2) A metropolitan water district created pursuant to Article 4.
(3) A metropolitan sewerage district created pursuant to Article 5.
(4) A metropolitan water and sewerage district created pursuant to Article 5A.
(5) A county water and sewer district created pursuant to Article 6.