Except there are ocean sized underground cavities! Ogallala Aquifer (High Plains Aquifer): Located in the central United States Underlies about 174,000 square miles (450,000 km²) across eight states One of the world's largest aquifers by volume Great Artesian Basin: Located in Australia Covers approximately 1,711,000 km² (660,000 square miles), about one-fifth of Australia Estimated water storage volume of 64,900 trillion liters (14,200 trillion gallons) Considered the world's largest aquifer by area Global deep groundwater: A 2021 study estimated there are around 20 million cubic kilometers of deep groundwater (below 2 km depth) Combined with shallower groundwater, the total underground water is estimated at 44 million cubic kilometers This makes underground water the largest reservoir of water on land, surpassing the volume of Earth's ice sheets Other major aquifers mentioned: Guarani Aquifer System (South America) North China Aquifer System Indus-Ganges-Brahmaputra Basin (South Asia) Nubian Aquifer System (North Africa) Arabian Aquifer System (Middle East)