The more water is extracted from underground, the harder it becomes to restore the region’s rivers and reservoirs — some of which no longer flow through the summer — simultaneously sucking them dry from above and below.

“If you don’t connect the two, then you don’t understand the system,” said John Bredehoeft, a leading hydrogeologist who for many years managed the U.S. government’s western states water program for the U.S. Geological Survey. “And if you don’t understand the system, I don’t know how in the hell you’re going to make any kind of judgment about how much water you’ve got to work with.”