Whenever the funds of the district are in excess of the amount necessary to complete the construction of the irrigation works or to acquire the property and rights in property necessary therefor, to supply all the land with sufficient water for irrigation purposes, and to pay every obligation of the district that is due and payable or that will, or probably will, become due and payable before the expiration of two years from the date on which the last preceding tax of the district was levied, the board may direct the treasurer to pay with the excess, specifying the amount, the portion of the sold general obligation bonds of the district as the excess sum of money will redeem at the lowest value at which they may be obtained for liquidation.