http://finance.yahoo.com/real-estate/article/111186/the-ten-biggest-american-cities-that-are-running-out-of-water

The water problem is worse than most people realize, particularly in several large cities which are occasionally low on water now and almost certainly face shortfalls in a few years. This is particularly true if the change in global weather patterns substantially alters rainfall amounts in some areas of the US.
..................
One goal was to identify potential conflicts in regions that might have disputed rights over large supplies of water and the battles that could arise from these disputes. And, 24/7 Wall St. examined geographic areas that have already been plagued by drought and water shortages off and on.

This article predictably avoids any discussion of the real cause.