You know the admonition to drink eight glasses of water a day to remain hydrated. But the truth is when you consider the water needed to produce what we eat -- think of it as virtual water -- we consume a lot more.
If we consider the water used in producing our foods, California is a net-importer and the Mid-West a net exporter.
The US as a whole then exports our water so the rest of the world can eat it.
From Craftsmen Quarterly, The Water We Eat.