Deep beneath the bleached-out, dusty surface of the drought-stricken West is a stash of water sequestered between layers of rock and sometimes built up over centuries.
Officials in the Colorado River basin states have long treated this liquid treasure as a type of environmental retirement account — an additional supply of water they can raid to get through the driest years and make up for the chronic overuse of the rivers themselves.
In recent years, the withdrawals have taken on even more importance: At least 60 percent of California’s water now comes from underground, some researchers say. Arizona, staring down imminent rationing of Colorado River water, pumps nearly half its supply from aquifers.
But in allowing their residents to tap underground resources this way, regulators and legislators in Southwestern states have ignored an inconvenient truth about how much water is actually available for people to use: In many places, groundwater and surface water are not independent supplies at all. Rather, they are interconnected parts of the same system.
The science has been clear for the better part of a century. Drawing groundwater from near a stream c... Read more