Without addressing aquifer depletion, which is a real problem in places like Australia(1), his assertion that distribution is the true difficulty doesn't really hold water.
Gee, I was just looking for references to Los Angeles and the American Midwest sinking due to aquifer depletion. And, finally, here is one that mentions the Ogallala Aquifer of the American Midwest: http://academic.evergreen.edu/g/grossmaz/WORMKA/
(1) http://en.wikipedia.org/wiki/Great_Artesian_Basin#Water_sour...