The Earth's population has more than doubled over the last 50 years and the demand for fresh water -- to drink and to grow food -- has surged along with it. But sources of water like rainfall, rivers, streams, reservoirs, certainly haven't doubled.
So where is all that extra water coming from? More and more, it's being pumped out of the ground.
Water experts say groundwater is like a savings account -- something you draw on in times of need. But savings accounts need to be replenished, and there is new evidence that so much water is being taken out, much of the world is in danger of a groundwater overdraft.
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