As the drought outlook for the Western U.S. becomes increasingly bleak, attention is turning once again to groundwater – literally, water stored in the ground. It is Earth’s most widespread and reliable source of fresh water, but it’s not limitless.
Groundwater flows through tiny spaces within sediments and their underlying bedrock. At some points, called discharge areas, groundwater rises to the surface, moving into lakes, rivers and streams. At other points, known as recharge areas, water percolates deep into the ground, either through precipitation or leakage from rivers, lakes and streams.
Groundwater depletion can also cause wells to run dry when the top surface of the groundwater – known as the water table – drops so far that the well isn’t deep enough to reach it, leaving the well literally high and dry. Yet until recently, little was known about how vulnerable global wells are to running dry because of declining groundwater levels.
There is no global database of wells, so over six years we compiled 134 unique well construction databases spanning 40 different countries. In total, we analyzed nearly 39 million well construction records, including each well’s location, the reason it was constructed and its depth.
Our results show that wells are vital to human livelihoods – and recording well depths helped us see how vulnerable wells are to running dry.
Millions of wells at risk
Our analysis led to two main findings. First, up to 20% of wells around the world extend no more than 16 feet (5 meters) below the water table. That means these wells will run dry if groundwater levels decline by just a few feet.
Second, we found that newer wells are not being dug significantly deeper than older wells in some places where groundwater levels are declining. In some areas, such as eastern New Mexico, newer wells are not drilled deeper than older wells because the deeper rock layers are impermeable and contain saline water. New wells are at least as likely to run dry as older wells in these areas.
– Sell the property. This is often considered if constructing a new well is unaffordable. Drilling a new household well in the U.S. Southwest can cost tens of thousands of dollars. But selling a property that lacks access to a reliable and convenient water supply can be challenging.
– Divert or haul water from alternative sources, such as nearby rivers or lakes. This approach is feasible only if surface water resources are not already reserved for other users or too far away. Even if nearby surface waters are available, treating their quality to make them safe to drink can be harder than treating well water.
– Reduce water use to slow or stop groundwater level declines. This could mean switching to crops that are less water-intensive, or adopting irrigation systems that reduce water losses. Such approaches may reduce farmers’ profits or require upfront investments in new technologies.
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– Limit or abandon activities that require lots of water, such as irrigation. This strategy can be challenging if irrigated land provides higher crop yields than unirrigated land. Recent research suggests that some land in the central U.S. is not suitable for unirrigated “dryland” farming.
State and local agencies can distribute groundwater permits in ways that help stabilize falling groundwater levels over the long run, or in ways that prioritize certain water users. Enacting and enforcing policies designed to limit groundwater depletion can help protect wells from running dry. While it can be difficult to limit use of a resource as essential as water, we believe that in most cases, simply drilling deeper is not a sustainable path forward.
The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.