Nature recycles the Earth's water supply through a process known as the water cycle or hydrological cycle. The hydrological cycles includes evaporation, condensation, precipitation, run-off, infiltration, and percolation. Of that 450 billion gallons only 100 billion gallons are actually consumes, the rest is returned to rivers or the ground. Industry withdraws the greatest volume of water, but does not consume the greatest amount. Much of the water withdrawn for industry is discharged after being used for cooling or other purposes.
Agriculture is the biggest consumer of water through irrigation.
It takes over 1 million gallons of water a year to irrigate one acre of farmland in arid conditions. More than 800.000 new water wells are drilled in the United States each year. The average person in the United States uses 176 gallons of water each day. Groundwater is twenty-five times more abundant than all the lakes, reservoirs and rivers of the world combined. The total volume of groundwater beneath the United States has been estimated at 125,000 cubic miles.