Cal. Pub. Util. Code § 16036

In lieu of appointing a treasurer, the board may elect that the duties of treasurer be performed by the treasurer of the county in which the district, or the greater part of its population, is situated. Whenever the board by ordinance so determines, such duties shall be performed by the county treasurer. The ordinance shall also prescribe the manner in which money is to be drawn out of the various funds belonging to the district in the hands of the treasurer. The treasurer shall be served with a certified copy of the ordinance.