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.

地下水井为数十亿人供水，但地下水位下降时，地下水井可能会枯竭。在这里，我们分析了约3,900万口全球分布的油井的施工记录。我们发现，有6至20％的井深不超过地下水位5米，这意味着如果地下水位仅下降几米，就有数百万口井处于枯竭的风险。此外，在某些地下水位明显下降的地方，新井的建造深度没有老井的深，这表明如果地下水位继续下降，新井的枯竭可能性至少与旧井一样。深层含水层的水质差以及建造井的高昂费用限制了开采深层地下水以防止井干时失去水源的有效性。