Underground water isn’t something most people think about when they turn on a tap or buy a bag of wheat flour at the grocery store. It’s invisible, ancient, and until recently, assumed to be practically endless. That assumption is turning out to be one of the more costly errors in the history of American resource management.
The United States relies on groundwater for roughly a quarter of its entire water supply, pumping approximately 82.3 billion gallons to the surface each day according to the U.S. Geological Survey. More than half of all American aquifers are now losing water, and in about one in eight of them, the collapse of underground water levels has actually sped up during the 21st century. What follows is a closer look at the six major systems where the problem is most urgent.
The Ogallala Aquifer: America’s Vanishing Breadbasket Foundation
The Ogallala Aquifer, also known as the High Plains Aquifer, remains America’s largest groundwater reserve, spanning eight states and powering the nation’s agricultural heartland. Yet pumping for irrigation far exceeds the aquifer’s slow recharge rate, with water table declines of over 200 feet recorded in parts of Texas and Kansas. It provides roughly 30 percent of the groundwater used for irrigation across the entire country and supports around a fifth of the nation’s agricultural output.
The Ogallala has been declining for decades because of overuse to irrigate crops in otherwise arid parts of the region. According to preliminary data presented to the Kansas House Water Committee, aquifer levels in the groundwater management area covering southwest Kansas fell by 1.52 feet between January 2024 and January 2025, a larger drop than the 1.43-foot decline the year before. Once depleted, the aquifer would take over 6,000 years to replenish naturally through rainfall – a sobering figure that puts the current rate of extraction in a very different light.
The California Central Valley Aquifer: The Food System’s Most Precarious Underpinning
California’s Central Valley supplies roughly a quarter of all food consumed in the United States, with an estimated value of seventeen billion dollars per year. The region is the second most-pumped groundwater aquifer system in the country, driven by widespread irrigated agriculture and a significant increase in permanent crops like vineyards and orchards. More than 76 of California’s aquifer basins are pumping water out faster than it can refill.
Groundwater in the Central Valley is at risk of being depleted by pumping too much water during and after droughts. Research shows groundwater storage recovery has been dismal after the state’s last two major droughts, with less than a third of groundwater recovered from the drought that spanned 2012 to 2016. A recent technical report found that land sinking due to over-pumping has already restricted how much water the State Water Project can deliver annually, and if no action is taken, the current trajectory of subsidence combined with climate change could reduce those deliveries by close to 90 percent by 2043.
The Colorado River Basin Aquifers: A Hidden Crisis Beneath a Visible One
As the Colorado River’s giant reservoirs have declined over the last two decades, even larger amounts of water have been pumped and drained from underground. Scientists at Arizona State University examined more than two decades of satellite measurements and found that since 2003, the quantity of groundwater depleted in the Colorado River Basin is comparable to the total capacity of Lake Mead, the nation’s largest reservoir. Some 40 million Americans rely on water from these aquifers, including in parts of Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming.
A separate analysis found that total water losses across the Colorado River Basin have accelerated significantly, with the rate of depletion from 2015 to 2024 averaging roughly three times faster than from 2002 to 2014. The Colorado River itself has seen a 20 percent decrease in flow over the past 100 years, with expectations that by mid-century it might decline another 30 percent. As access to surface water diminishes, it places growing pressure on groundwater as the only backstop against running out entirely.
The Arizona Lower Colorado River Basin Aquifers: Exceeding Lake Mead’s Entire Capacity
A peer-reviewed study published in March 2025 revealed that Arizona’s groundwater depletion in the Lower Colorado River Basin has exceeded the full capacity of Lake Mead by 40 percent. Around 68 percent of the losses in the broader Colorado River Basin occurred in the lower part of the basin, which lies mostly in Arizona. The scale of that figure is worth sitting with – Lake Mead is the largest reservoir in the entire country, and Arizona has already lost more than that volume from underground.
Most of the depletion in the lower Colorado River Basin occurs in Arizona due to agricultural pumping, and annual losses average over 1.2 million acre-feet. A University of Texas projection from 2025 indicated that up to 70 percent of the Texas Panhandle portion of its connected aquifer systems could become unusable within 20 years if current pumping rates continue. Management efforts exist, though active management areas formed as part of the Arizona Groundwater Management Act of 1980 have cut down water losses in some areas, suggesting that regulation, when applied at adequate scale, can make a real difference.
The Great Basin Aquifers: Where Even Record Snowfall Isn’t Enough
Even in years of record snowfall, like the remarkable 2022 to 2023 winter, researchers expected the precipitation to help replenish the groundwater supply – but the decline continued. The research, published in 2024 in Geophysical Research Letters, found that a major reason for the ongoing decline is upstream water diversion for agriculture and households. Populations in the states that rely on Great Basin water supplies have grown by 6 to 18 percent since 2010, and as population increases, so does water use.
Global warming causes more surface water to evaporate before it has a chance to seep through the ground and replenish aquifers, so groundwater is replenishing at a slower rate. Extreme weather events like droughts exacerbate the problem through lack of rainfall, and even unusually heavy precipitation can be counterproductive when water gathers at the surface and rushes off into lakes and oceans at a faster rate instead of soaking in. Estimated groundwater depletion in the United States from 1900 to 2008 totaled approximately 1,000 cubic kilometers, with the rate increasing markedly since about 1950 and reaching its maximum pace in the years between 2000 and 2008.
The Atlantic Coastal Plain Aquifer: Saltwater, Sinking Land, and Suburban Demand
In Nassau and Suffolk Counties on Long Island, New York, pumping water for domestic supply has lowered the water table, reduced or eliminated the base flow of streams, and has caused saline groundwater to move inland. Many other locations on the Atlantic coast are experiencing similar effects related to groundwater depletion. This is a region people rarely associate with a water crisis – yet the long-term data tell a different story.
Many regions of the country are experiencing groundwater depletion because aquifers are being pumped faster than they can be replenished. Roughly 45 percent of the water wells examined in a major analysis showed a statistically significant decline in water levels since 1980, with approximately 40 percent reaching record-low water levels during the past decade. Groundwater aquifers suffer from a persistent lack of regulation, with the federal government playing almost no role and individual states implementing a wide range of often weak rules. Without stronger oversight along the Atlantic Coastal Plain, the quiet erosion of this water supply will continue well beneath public notice.
The Bigger Picture: What Depletion Actually Costs
If unregulated pumping reaches its logical conclusion, aquifers could be left depleted, with estimated recovery times running into centuries or even millennia. The consequences extend well beyond farms. Water wells can dry up over time, the level of water in streams and lakes can drop, land subsidence can become more common as soil collapses when water is removed, and water quality can deteriorate.
So much groundwater is now being pumped that it is filling the oceans as it drains off land, becoming one of the largest drivers of global sea level rise. Climate change is reducing the amount of water going to recharge aquifers, while rising temperatures mean crops require more water to grow – and one study found that the rate of groundwater depletion in the Ogallala alone could increase by as much as 50 percent by 2050. The pace, in other words, is not fixed. It is accelerating.
