California Code, Public Resources Code - PRC § 5572.1

Where the annexation of territory to a district would otherwise be valid, except that such annexed territory was not within the boundaries of a municipal utility district organized and existing under Chapter 218 of the Statutes of 1921,  1 or the Municipal Utility District Act, such annexation shall be valid.  This section shall be applied retroactively to validate the annexation of such territory to a district as of the date that the annexation would otherwise have been valid.