At a rate of 20 million acre feet per year how many years will it take to deplete an aquifer containing 3.3 billion acre feet of water?

Answer 1

3.3 billion divided by 20.0 million = 165 years

That's assuming the aquifer has zero rainfall to replenish it. Hydrogeology is extremely complex with many variables and it is difficult/impossible to estimate total aquifer recharge. For the Edwards Aquifer in Central Texas, it's estimated at 700,000 acre-feet per year, pre-drought that is. So if you're pumping 20.0 million out and the recharge is less than 1.0 million, you're at a negative 19.0 million per year. Pretty upside down if you ask me.

One source claims 1 acre-foot of water equals 325,851 gallons of water and serves 4 people (one family in theory) for one year. That's 80,000 gallons per person per year. Seems extremely high...

Another source (HUD) says the average family of three uses about 100,000 gallons of water per year - based on 45k gallons inside and 55k gallons outside - assuming a St. Augustine lawn. This calcs out to about 33,333 gallons per person per year. Seems more reasonable...

Based on this, 20.0 million acre-feet per year, or 6.5 trillion gallons per year, serves the needs of 195.0 million people for one year. More or less two thirds of the population of the United States.

Note that this only looks at household (inside and out) water use and not industrial water use, Golf courses, power plants, fountains, public Swimming Pools, city grounds and gardens, and on and on....

Hope this helps...

Alex.Tango.Fuego