The directors or other officers or employees of a district shall have no power to incur any indebtedness or liability in excess of the amount of money available under the provisions of this division. Any debt or liability incurred in excess of the express provisions of this division is void. Except, however, that nothing in this section shall prevent the directors from borrowing from such federal, state, county, public or private funds which are, or which may in the future become, available to the directors for the furthering of the work of the district in any manner or by the sale of bonds payable solely from any revenue of the district, if the assets acquired by such a loan or bond constitute the entire security for the loan or bond and if no indebtedness or liability is incurred by the directors in excess of the amount of the assets acquired.