A body of permeable rock or unconsolidated sediment that can store and transmit significant quantities of groundwater. Aquifers serve as the primary source of well water worldwide.
An aquifer is a geological formation composed of permeable materials such as sand, gravel, fractured rock, or limestone that is capable of storing and yielding usable quantities of groundwater. Aquifers function as underground reservoirs, receiving water through recharge processes and releasing it through natural discharge or pumping wells. They are classified based on their hydraulic properties into confined and unconfined types. Confined aquifers are bounded above and below by impermeable layers called aquitards, while unconfined aquifers have the water table as their upper boundary. The productivity of an aquifer depends on its porosity, permeability, thickness, and areal extent. Aquifers are critical components of the hydrologic cycle, supplying roughly 30% of the world's freshwater for drinking, irrigation, and industrial use. Their sustainable management requires understanding recharge rates, storage capacity, and the impacts of pumping on water levels and quality.