To meet the expenses of operation and maintenance and the sinking fund and interest charges on the bond issue when the income derived from the works is not sufficient to meet such charges, the board of commissioners of any such electric light, water supply, fire protection or sewerage district shall each year before the levying of taxes make up an estimate or budget for such district, which shall give the estimated maintenance and expenses for the succeeding year and shall submit it to the county supervisor for approval and adoption. Any surplus or deficit that may occur in any one year shall be carried forward and applied to the next year’s account and properly considered in the budget for the expenses of the district for the ensuing year.