(a) A water and sewer utility as to rates or services may not make or grant any unreasonable preference or advantage to any corporation or person within any classification or subject any corporation or person within any classification to any unreasonable prejudice or disadvantage.
(b) A utility may not establish and maintain any unreasonable differences as to rates of service either as between localities or as between classes of service.
(c) For purposes of this section, a reduced rate authorized under Section 13.182(b-1) does not:
(1) make or grant an unreasonable preference or advantage to any corporation or person;
(2) subject a corporation or person to an unreasonable prejudice or disadvantage; or
(3) constitute an unreasonable difference as to rates of service between classes of service.