Public Utilities Code § 13131

So long as any bonds of the district are outstanding and unpaid, or so long as provision has not been made for the full payment and discharge of all such outstanding bonds, upon maturity, or upon redemption prior to maturity, through the setting apart in a reserve fund or special trust account created pursuant to this article to insure the payment thereof, of money sufficient for that purpose, or through other irrevocable allocation to that purpose of money sufficient therefor all provisions of this article shall be complied with.