The depletion of groundwater in the Upper Colorado River Basin poses significant risks to water availability for over 40 million people across seven U.S. states and Mexico. The loss of groundwater, which supports rivers and reservoirs, could exacerbate water shortages for agriculture, urban areas, and ecosystems. The study underscores the need for sustainable water management practices, as groundwater can no longer be considered an unlimited backup resource. The findings also highlight the interconnectedness of surface and groundwater systems, suggesting that declining groundwater levels could further strain already stressed surface water supplies.