Annually, on or before the date set for the consideration of the budget by the board of supervisors of the county in which the district is located, the board of each district shall furnish to the board of supervisors of the county in which the district is situated, an estimate in writing of the amount of money needed for all purposes by the district during the ensuing fiscal year. Thereupon, it is the duty of the board of supervisors to levy a special tax, on all taxable property of the county lying within the district, sufficient in amount to raise that sum.