In any proceeding pending after January 1, 1996, the commission shall apply this article in its consideration of any matter concerning the sale by a water corporation of real property that is not necessary or useful in the provision of water utility service, for any sale that occurred prior to that date. If the water corporation has not invested the net proceeds therefrom in utility infrastructure, plant, facilities, and properties that are necessary or useful in the provision of water service to the public, it may elect to do so during the period provided in subdivision (c) of Section 790 and that period shall be deemed to have commenced as of January 1, 1996.