Originally Posted by aka123

Although the problem in dry areas using fossil water or regular groundwater too much, is that the rain will mostly come down elsewhere.

This is biggest problem in Middle-East, as there rains very little.

"The Nubian Sandstone Aquifer System is among the most notable of fossil water reserves. Fossil aquifers also exist in the Sahara, the Kalahari, and the Ogallala underlying the US Great Plains. A further potential store of ancient water is Lake Vostok, a subglacial lake in Antarctica."

http://en.wikipedia.org/wiki/Fossil_water