Fundamentally, it's related to private mineral ownership in Texas and the "Rule of Capture." Except for some specific groundwater district areas, a landowner can pump as much water as he wants, subject to the maximum capacity of the water well.

Also, the mineral estate and the surface estate can be severed. In other words, you can own the surface but not any of the mineral rights. I think that what Pickens did is to simply purchase all ground water rights underlying a large chunk of land over the aquifer.

In regard to "The Worst Hard Time," it is an excellent book. The suffering of the people that stayed in the Dust Bowl areas was almost beyond belief.

As I noted on Drumbeat, there were parts of Texas that were abandoned because of a lack of water in the Fifties.

BTW, note that the leading "solution" to the looming water crises in the US is to process brackish water and saltwater, presumably using reverse osmosis, which is of course hugely energy intensive.