Residential, agricultural and industrial wells are being dug deeper and deeper in search of freshwater, according to the first nationwide assessment of U.S. groundwater wells. But scientists warn that the practice is not a sustainable way to address the country’s future water supply needs.
In the United States, groundwater is a source of drinking water for more than 120 million people and supplies nearly half of the water used for irrigating crops. But water levels are dropping in many major aquifers supplying large populations and farming regions, including California’s fertile Central Valley (SN: 3/3/18, p. 9) and the High Plains region atop the vast Ogallala aquifer. The Ogallala, which underlies parts of eight states from South Dakota to Texas, is of particular concern: A 2017 report by the U.S. Geological Survey noted that its water levels had dropped by more than three meters on average from 1950 to 2015.
Digging deeper wells is one response to dropping water levels, but it was unclear how widespread that trend was. Debra Perrone, a water resources engineer, and hydrologist Scott Jasechko, both of the University of California, Santa Barbara, compiled data on about 11.8 million wells built from 1950 to 2015. During that time, wells have gotten deeper across 79 percent of the country, the team reports July 22 in Nature Sustainability. Average well depth is currently about 60 meters below the surface, the researchers say, although it varies widely.
It’s more expensive to sink a deeper well and requires more energy to pump the water out. Deeper wells can also tap into saltier water, requiring desalination. As a result, the trend may contribute to water access inequities, the researchers argue. Less wealthy areas may struggle to keep up with the race to reach and treat water pumped from greater depths.
Editor’s note: This story was updated July 30, 2019, to correct the time range when the studied wells were built (starting in 1950, not 1975) and that wells got deeper across 79 percent of the country, not 70 percent.