The actual amount of water that enters the ground water zone for any specific area depends upon the annual rainfall in that area. Of that 450 billion gallons, only 100 billion gallons are actually consumed. The remaining 350 billion gallons are withdrawn for nonconsumptive industrial and agricultural uses. Industry is the largest withdrawer of water but not the largest consumer. Much of the water withdrawn for industry is returned to its source after being used for cooling or other purposes.
Agriculture is the largest user of water due to irrigation.
It takes over 1 million gallons of water a year to irrigate one acre of farmland in arid conditions. Most of the water used by irrigation re-enters the hydrologic cycle through evapotranspiration. On average, Americans use approximately 75 to 80 gallons of water per person per day. Much of this water eventually returns to the water supply after having passed through a waste water treatment facility or domestic septic systems.