Equation (2) also shows that any investment in infrastructure that increased national benefits by more than the cost of the investment is justified economically. In fact the economic value of these improvements are what can be used to pay for the investments. From the private financial view, it is the net present value of additional net farm income minus the cost of developing the infrastructure. For a national economic view it is the net present value of additional benefits from all water users minus the cost of developing the infrastructure. In irrigated systems, the optimum level of irrigation infrastructure differs for different levels of water availability, but only one level of irrigation capacity can be maintained in the short run once that capacity has been established.