(a) A municipality that makes a wholesale sale of water to a special district created under Section 52, Article III, or Section 59, Article XVI, Texas Constitution, and that operates under Title 4 or under Chapter 36 shall determine the rates for that sale on the same basis as for other similarly situated wholesale purchasers of the municipality's water.
(b) This section does not apply to a sale of water under a contract executed before the effective date of this section.