Seven Western states have just received an overdraft notice from nature’s water bank, written in red ink, all caps. It turns out that three-fourths of the H2O they’ve been using during the American West’s record drought (14 years and counting) has been drawn from their precious savings account: not the Colorado River itself but aquifers below ground.
The significance of this discovery, by scientists looking at a series of satellite measurements of the river basin, can hardly be overstated. The West has to measure and manage its underground water at least as carefully as it does the surface supply, and find new ways to drastically conserve.
The Colorado’s surface water is measured and parceled out to 40 million people and 4 million acres of farmland in the basin according to the “Law of the River,” a collection of almost a dozen agreements among seven states, the federal government and Mexico. That surface supply is diminishing in the present drought, as is obvious from photos of a 130-foot-deep bathtub ring around Lake Mead. This reservoir behind the Hoover Dam is at its lowest level since it was filled in the 1930s.
Until now, however, no one realized the extent to which Westerners were using underground water to make up the shortfall. That knowledge required NASA satellite measurements of water mass below the surface. Since the end of 2004, the researchers found, two Lake Meads worth of water have been drained from Colorado Basin aquifers.
The states are in charge of managing their own underground water, and many of them don’t. No one knows how much of it is left, or if the withdrawals of recent years will soon be replenished. This makes it difficult, to say the least, to ensure that water use is sustainable.
What’s needed are measurements of underground water tables — this can be done by measuring a series of local wells — and a plan to keep those levels from falling farther. The Central Arizona Groundwater Replenishment District has done this and, at least until the drought began at the start of this century, was able to keep the water levels stable.
This strategy should be expanded, and ideally states and cities throughout the basin would coordinate new efforts to monitor and conserve groundwater. However much is there, it is not infinite, and states would be foolish to keep blindly tapping it as if it were.
One creative strategy to reduce demand is the Colorado River System Conservation Program, a pilot project in which water users in Denver, Las Vegas, Los Angeles and Phoenix will pay regional farmers and industries millions of dollars to use less water more efficiently. Farms, after all, account for 80 percent of Colorado River water use.
At the same time, people also need to use less water. And water agencies can give them the incentive by charging more for water use beyond what’s needed for drinking and keeping clean. If more effective voluntary measures are not taken to manage the Colorado’s ebbing supply, then the entire U.S. Southwest could find itself facing the same predicament.