The board of supervisors may, from time to time, transfer moneys to the district, for the benefit of the zone, from any available funds of the county. Any moneys so transferred are hereby appropriated, and shall be used, for the payment of any currently payable expenses incurred by reason of the removal of the obsolete system and the installation of the modern system proposed for the zone, and for the cost of maintenance thereof prior to December 1st of the first fiscal year in which a special tax or assessment may be levied in and on behalf of the zone. All costs of maintenance of the modern system, subsequent to that date, shall be budgeted and included in the general levy of taxes or assessments, as the case may be, in and on behalf of the district as a whole.