A sweeping new map of groundwater under the continental United States is pulling back the curtain on where water actually sits beneath our feet, how deep you need to drill to reach it and where the trouble spots really are. The picture is both massive and sobering. There is a huge national reserve, but in local hot spots like California, the shortages are sharp enough to matter to farmers, cities and rural households right now.
For water managers, the ultra-detailed view could reshape decisions about where to pump, where to recharge and where to conserve before the next round of dry wells and sinking land arrives.
Researchers at Princeton University and the University of Arizona built the map by training machine-learning models on millions of well records and layers of geological data, according to Princeton University. They fed the system more than a million direct groundwater measurements plus climate and subsurface information, then used it to predict water table depths even in places with no existing wells. The resulting product clocks in at roughly 30-meter resolution, and the underlying data have been released for public use after publication in a peer-reviewed journal.
The team estimates there are about 306,500 cubic kilometers of accessible groundwater, roughly 250 billion acre-feet and more than 13 times the volume of the Great Lakes, based on the public dataset hosted on Zenodo. That total comes from combining predicted water table depth with estimates of rock porosity across an 8 billion cell grid and reporting uncertainty for every pixel. The fine scale means managers can now see differences within a single valley that older, coarse maps simply blurred together.
None of that means the water is evenly spread. In California, where the new map highlights some of the deepest and most stressed aquifers in the country, the Los Angeles Times reports that the U.S. Geological Survey estimated the state had lost about 128 million acre-feet of groundwater as of 2019, a volume comparable to Lake Tahoe. The same report notes that California's dry well database shows about 6,000 domestic wells have gone dry since 2013, although only 13 were reported in the past year.
"The scientists convincingly show that it is now possible to simulate groundwater depths and availability at very high resolutions," Jay Famiglietti, a hydrologist at Arizona State University who was not involved in the research, told the Los Angeles Times, calling the work "a remarkable achievement." He added that the map is a strong complement to satellite measurements, but that the country still needs a national-scale network of deep groundwater wells to track both quantity and quality all the way down to bedrock. In other words, the new map is a powerful decision-support tool, not a final, carved-in-stone inventory.
How managers can use the map
The study team has made the national map and regional products available through the project data portal and the HydroFrame platform, where agencies and researchers can grab high resolution TIFF files and basin level views. That level of detail can help officials choose where to site new wells, pinpoint the best locations for managed aquifer recharge and highlight which small streams and wetlands are most vulnerable when shallow groundwater is drawn down.
Local planners say those practical uses are exactly what is needed to head off the next wave of domestic wells going dry and the kind of land subsidence that buckles roads and cracks canals.
What the map does not tell us
The authors are clear that this is a "modern estimate" stitched together from observations collected between the early 20th century and 2023. In practice, that means the product blends measurements taken at different times rather than delivering a single, date stamped snapshot. The machine-learning approach fills in spatial gaps, but it does not replace the kind of time series monitoring needed to track ongoing depletion or recovery at specific wells.
Researchers hope the map will spur investment in deeper, more consistent groundwater monitoring and more transparent local reporting so that future versions can capture change over time, not just a best-available average picture.
For now, the new map reframes the stakes. The United States is sitting on vast groundwater reserves, but the places where water is shallow and relatively easy to tap are often not the same places where demand is most intense. Managers and communities now have a much sharper tool to match local decisions with underground realities, provided policymakers and utilities follow through with the monitoring networks and recharge programs needed to put it to work.
