The board shall determine annually the amount of money necessary to be raised by a levy on the taxable property in the district, taking into consideration other sources of revenue of the district, and shall fix a rate of levy which, when levied upon every dollar of valuation for assessment of taxable property within the district, together with other revenues, shall raise the amount required by the district during the ensuing fiscal year for paying expenses of organization and the costs of acquiring, constructing, installing, operating, and maintaining the improvements or works of the district or providing the services of the district and promptly to pay in full when due all interest on and principal of general obligation bonds or indebtedness and other obligations of the district. In the event of accruing defaults or deficiencies, additional levies may be made as provided in section 30-20-516. At the time of certifying other tax levies, the board shall certify to the board of county commissioners of each county in which the district or a portion thereof lies the rate of levy so determined with directions that, at the time and in the manner required by law for levying of taxes for county purposes, such board of county commissioners shall levy such tax upon the valuation for assessment of all taxable property within the district at the rate so fixed and determined, in addition to such other taxes as may be levied by such board of county commissioners.