Water resources
Groundwater
Definition
Groundwater is water found underground in the cracks and pore spaces of soil, sand, and rock, stored in and moving through geological formations called aquifers. It originates mainly as precipitation that infiltrates below the land surface past the water table into the saturated zone, and it discharges naturally to springs, rivers, wetlands, and oceans. There is vastly more water in the ground than in all the world's rivers and lakes combined.
References
definition, store size, cycle
Overview
What it means
Groundwater is the world's largest accessible store of liquid freshwater, supplying a large share of drinking water and irrigation. Its invisibility is its vulnerability: abstraction can exceed recharge for decades before wells fail, and contamination is slow to appear and slower to remediate. Recharge — natural and managed (managed aquifer recharge) — determines whether use is sustainable.
How it is used
The term frames water-resource management, drought resilience, and regulation of abstraction; managed aquifer recharge and conjunctive use with surface water are key adaptation strategies.
Why it matters
Aquifer depletion is a silent, often irreversible sustainability failure unfolding beneath many of the world's breadbaskets and cities. **Note:** 1315 Groundwater recharge merges into this entry; recharge processes are covered here.