When the state of Washington shall be required to make any payment or expend any money in the performance of any such contract entered into with the United States, an estimate of the amount of expenses likely to be incurred in such performance, together with an estimate of future losses or damages that may occur under such contract shall be made by the director of ecology, who shall thereupon return a statement thereof to such district, and the board of directors of such district shall from time to time as required by the director of ecology levy against all the property within said district such assessments as may be necessary to repay to the state of Washington such estimated expenses, losses and damages. PROVIDED, If such district has no money in the “The Indemnity Fund” to repay such expenses when the same shall be incurred or to pay such losses and damages as the same shall accrue it shall be the duty of the board of directors to cause warrants of the district to be issued in payment of such indebtedness, which warrants shall bear interest at a rate determined by the board and be paid from moneys paid into the indemnity fund by assessments levied as hereinbefore provided.