Those aquifers that we are so assiduously mining in the West: why weren't they exhausted long ago? After all, surface waters in New Mexico have been fully appropriated since at least 1848.
The answer lies in well technology. With the development of more powerful pumping technology, the deeper waters became accessible. This has led to a temporary, illusory increase in water supply.
It also explains why the water situation in Roswell, New Mexico in the early part of the 20th century was so noteworthy. The deep aquifer there is a special kind, an artesian aquifer. This means that there is so much pressure on the water in the aquifer, that when you drill a well into it, the pressure sends the water shooting skyward. In Roswell a pump wasn't necessary. Mother Nature would pump the water for you.
Unfortunately for the people living along the Pecos River, excessive mining of the shallow and deeper groundwater led to a lowering of the pressure in the aquifer, a lowering of the water table, and along with it, the Pecos River. This reduced the amount of water available to downstream users in Carlsbad and also Texas and created all sorts of water management problems, including a huge lawsuit between Texas and New Mexico.