The lower Portneuf aquifer's future capacity to supply water is predicated on the amount of recharge, or water that flows into it every year. Like a bank account balance, if water withdrawals exceed water inflow, the amount of water in the aquifer will decrease. The aquifer's water balance indicates that future water withdrawals can rise to a total of about 7.5 billion gallons per year without affecting the aquifer's long-term storage. This figure shows a summary of the main inflows, outflows, and pumping withdrawals from the northern and southern portions of the lower Portneuf aquifer, as determined from a detailed water balance analysis performed in 1994 and recently updated. As of 1999, the total pumping withdrawals by the cities of Pocatello and Chubbuck exceeded 6.2 billion gallons annually. Thus, about 80% of the aquifer's water capacity is already tapped.