What is an aquifer?

An aquifer is fundamentally understood as a geological formation that has the capacity to both store and transmit groundwater. This means that it is composed of permeable materials, such as sand, gravel, or porous rock, which allow water to flow through them. Aquifers are crucial to the hydrological cycle, serving as significant sources of freshwater that can be tapped through wells or springs for agricultural, industrial, and domestic use.

The ability of an aquifer to store water is determined by its porosity, while its ability to transmit water is defined by its permeability. This dual function makes aquifers essential not only for providing resources but also for maintaining the ecological balance of freshwater systems.

Other options do not accurately represent the definition of an aquifer. For example, a natural reservoir for surface water describes surface water bodies rather than underground formations. A type of water treatment facility refers to man-made systems designed to treat and purify water, which is distinct from the naturally occurring aspect of aquifers. A chemical substance used in water purification is unrelated to the geological and hydrological characteristics of aquifers. Thus, the choice that defines an aquifer as a geological formation that stores and transmits groundwater is the only accurate representation.