Nature · Earth Science
The hidden ocean beneath our feet
Far more fresh water lies hidden underground than in all the world’s rivers and lakes combined. Soaking into the ground and stored in porous rock, this groundwater feeds springs, wells and wetlands, sustains rivers through droughts, and supplies drinking water to billions of people.
Rain and snowmelt seep down through soil and rock until they reach a zone where every pore is full of water — the water table. Water collects in permeable layers called aquifers, moving slowly through the rock and emerging naturally as springs wherever the water table meets the surface.
Rain infiltrates to the water table and fills an aquifer between rock layers, feeding wells and springs.
The top of the saturated zone
The water table marks where the ground becomes fully saturated. It rises after rains and drops in droughts — and wherever it meets the land surface, water seeps out as springs, seeps or wetlands.
Rock that holds and yields water
An aquifer is a body of permeable rock or sediment that stores and transmits water. Some hold “fossil water” that fell as rain millennia ago, recharged far slower than we pump it out.
Where groundwater returns to daylight
A spring is where groundwater emerges on its own. In an artesian system, water is trapped under pressure between rock layers and gushes upward when tapped — no pump needed.
Water sculpting soluble rock
Where groundwater dissolves limestone, it carves caves, sinkholes and underground rivers. These karst systems can burst back to the surface as powerful springs after journeys through the dark.