No district shall be permitted to contract obligations in excess of the estimated revenues for the two years next succeeding the incoming [incurring] of such indebtedness and it shall be unlawful for the county commissioners to approve of any bills which will exceed the revenue to any district which shall be estimated to be received by such district during the next two years.
RCW 17.12.100
County budget as limitation on incurring liability: RCW 36.40.100.