LAUSR

When your well runs dry Groundwater provides nearly half of the water used for agricultural irrigation and most of the drinking water for billions of people. It is essential, then, for this resource to remain secure. Jasechko and Perrone examined data from approximately 39 million wells in 40 countries worldwide to investigate their vulnerability to declining water levels (see the Perspective by Famiglietti and Ferguson). The authors found that construction of deeper wells is not occurring in some areas that are experiencing groundwater decline, a disconnect that poses risks for people who rely on well water. Science, this issue p. 418; see also p. 344 Across the world, many wells are at risk of running dry where groundwater levels are declining. Groundwater wells supply water to billions of people, but they can run dry when water tables decline. Here, we analyzed construction records for ~39 million globally distributed wells. We show that 6 to 20% of wells are no more than 5 meters deeper than the water table, implying that millions of wells are at risk of running dry if groundwater levels decline by only a few meters. Further, newer wells are not being constructed deeper than older wells in some of the places experiencing significant groundwater level declines, suggesting that newer wells are at least as likely to run dry as older wells if groundwater levels continue to decline. Poor water quality in deep aquifers and the high costs of well construction limit the effectiveness of tapping deep groundwater to stave off the loss of access to water as wells run dry.