Water, Waste & Pollution
Aquifer
A body of rock or sediment that stores and transmits groundwater in usable quantities — the source of wells and springs and the world's main store of accessible freshwater.
Definition
A saturated, permeable geological formation (rock or sediment) capable of storing and yielding groundwater in usable quantities. Its performance depends on porosity (the volume of pore space) and permeability (how connected those spaces are); clay-rich or impermeable layers above or below can confine it.
References
Definition; porosity, permeability and hydraulic conductivity; confining layers (aquitards/aquicludes).
Groundwater storage definition; recharge/discharge balance; GRACE satellite detection of overexploitation.
Overview
What it means
Aquifers recharge from rainfall and surface water percolating underground, and discharge through springs, rivers and wells. They range from small hillside formations to regional systems spanning several geological units.
Because recharge is slow, pumping can outstrip renewal — measurable from space by the GRACE gravity satellites as falling groundwater storage — leading to depletion, land subsidence and saltwater intrusion in coastal areas.
How it is used
Aquifers supply drinking water, irrigation and industry worldwide; they are managed through pumping limits, monitoring wells, and increasingly "managed aquifer recharge" schemes that deliberately store surplus surface water underground. Water-stewardship and disclosure frameworks assess operations against local aquifer stress.
Why it matters
Groundwater is the world's largest source of accessible liquid freshwater and the buffer against drought; aquifer depletion is a slow-moving crisis for food production and city water supplies, and once contaminated or compacted, aquifers are effectively impossible to restore on human timescales.
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