The primary source of water for 2.5 billion people is in danger

The Central Valley in California is a farming powerhouse, growing more than 250 crops and producing $17 billion of agricultural products every year to feed the world.

The competing demands of both agriculture and a growing local population — along with droughts made worse by the climate crisis — have put a dramatic strain on the local wells supplying groundwater for both the farmers and rural residents.

In short: the wells are literally running dry.

According to a new study, the same groundwater problem plaguing the Central Valley is occurring around the world, threatening the drinking water of billions of people.

“When wells run dry, people lose access to water in their homes and people lose access to a reliable source of water to produce crops that support their livelihood,” Debra Perrone, a co-author on the study and assistant professor of environmental studies at the University of California, Santa Barbara, tells Inverse.

What’s new — In a study published Wednesday in the journal Science, researchers report that up to 20 percent of groundwater wells are at risk of running dry. This is based on an evaluation of almost 39 million groundwater wells across 40 countries.

Groundwater is underground water found in the cracks and spaces between soil, sand, and rock. According to the United Nations, groundwater provides drinking water to at least 50 percent of the global population and represents 43 percent of all water used for irrigation. An estimated 2.5 billion people depend solely on groundwater for their basic daily water needs.

Why are the wells at risk of running dry? The study suggests it has to do with water depth.

When wells are only a few meters deeper than the underlying water table, the wells risk running out of water. A water table is an underground boundary between saturated and unsaturated ground.

The researchers found that up to 20 percent of wells in their study were only five meters deeper than the underlying water table.

If the wells decline by only a few meters more, then they could run out of water, jeopardizing the water supply for millions of wells — and many people.

Why is groundwater in danger?

The decline in groundwater levels has to do with groundwater pumping.

“There are numerous places where groundwater pumping is depleting groundwater reserves,” Scott Jasechko, lead author on the study and assistant professor of water resources at the University of California, Santa Barbara, tells Inverse.

And as climate change continues to exacerbate droughts, groundwater extraction increases.

“Because groundwater is a perennial resource that provides reliable water during droughts, overpumping and reductions in recharge are both often at play,” Perrone explains.

How they did it — The scientists spent five years painstakingly creating a dataset on groundwater wells from more than 100 databases and 40 countries.

In the end, they came up with a global dataset of 39 million wells, which they used to form their conclusions.

Another objective of the study was to examine whether recently constructed wells would face the same problem of groundwater depletion as older wells.

“One of our main findings is that newer wells are not much deeper than older wells in some of the places where groundwater levels are declining,” Jasechko says.

In other words: simply digging new wells won’t solve the problem of groundwater depletion.

“This means that newer wells are at least as vulnerable as older wells to running dry, should water levels continue to decline,” Perrone says.

Why groundwater matters

Groundwater provides the main water supply for nearly half of the drinking water and farming irrigation for billions of people around the world. This data suggests that up to 20 percent of groundwater wells are at risk of running dry.

According to Perrone, groundwater in the US provides water for 98 percent of rural residents in the U.S.

“Groundwater wells supply nearly half of all the water used for irrigation in America, making them critical to food production. What's more, nearly 150 million Americans get their tap water from groundwater,” Jasechko says.

What’s next — “Groundwater depletion is a complex problem. There is no single solution,” Perrone says. But there are a few options for making groundwater use more sustainable in the long use, she explains.

Some of these options rely on people to restrict unnecessary water use — like getting rid of water-sucking lawns — which will ultimately help curb declining groundwater levels

“We can reduce demand through behavioral changes or through the adoption of water-saving technologies,” Perrone says.

Shifting from groundwater to alternative water sources could also help us solve this growing water crisis, the study suggests. For example, in recent years desalination technology has taken off as alternative water — though it remains prohibitively expensive in many cases.

We can also “take advantage of excess water when it is available” to recharge our aquifers — underground rock layers that store and transport groundwater — according to Perrone.

The study team also makes a case for more science-informed regulation, monitoring of water networks, and better sharing of groundwater data around the globe.

In a related Perspective, scientists say this study is a “timely warning that universal access to groundwater is fundamentally at risk.” As groundwater levels decline, only the “relatively wealthy” will be able to access this critical resource.

“Disappearing groundwater resources may act as a trigger for violent conflicts and have the potential to generate waves of climate refugees. Avoiding such a scenario is clearly paramount to human security,” they write.

Abstract: 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.