WATER WELLS AT RISK OF RUNNING DRY IN US AND WORLDWIDE
AS THE drought outlook for the Western US becomes increasingly bleak, attention is turning once again to groundwater – water stored in the ground. It is Earth’s most widespread and reliable source of fresh water, but it’s not limitless.
Wells that people drill to access groundwater supply nearly half the water used for irrigated agriculture in the US and provide more than 100 million Americans with drinking water. But pervasive pumping is causing groundwater levels to decline.
As a water resources engineer, a water scientist and large-data analyst, in a recent study, we mapped locations and depths of wells in 40 countries across the world – and found millions of wells could run dry if groundwater levels decline by only a few meters.
Solutions vary, but most important for protecting wells from running dry is managing groundwater sustainably.
Today wells supply 40% of water used for irrigation worldwide and provide billions with drinking water.
Groundwater depletion can 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.
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 well construction databases spanning 40 countries. We analysed nearly 39 million well construction records, including each well’s location and depth.
Recording the well depths helped us see how vulnerable wells are to running dry. Our analysis led to two main findings. First, up to 20% of wells across the world extend no more than 5m below the water table. That means the wells will run dry if groundwater levels decline by just a few metres.
Second, we found that newer wells are not being dug significantly deeper than older wells in some places where groundwater levels are declining. Thus, the new wells are at least as likely to run dry as older wells in these areas.
How can households adapt when their well runs dry? Here are four strategies, all of which have drawbacks.
◆ Dig a new, deeper well. This is an option only if fresh groundwater exists at deeper depths. In many aquifers deeper groundwater tends to be more saline, so deeper drilling is no more than a stopgap solution. And since new wells are expensive, this approach favours wealthier groundwater users and raises equity concerns.
◆ 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.
◆ Households and communities can take proactive steps to protect wells from running dry. Activate a process to seek permission before allowing the withdrawal of groundwater.
◆ State and local agencies can distribute groundwater permits in ways that help stabilise falling groundwater levels over the long run, or in ways that prioritise 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.