70 ILCS 3705/15

No money shall be paid out of the treasury of the district, except upon an order signed by the Chairman and Secretary of the board. Such order shall specify the purpose for which the amount thereof is to be paid, with sufficient clearness to indicate the purpose for which the order is issued, and the name of the particular fund out of which it is payable, and it shall be payable from the fund constituted for such purpose and no other.