What type of water is referred to in an aquifer?

An aquifer is specifically defined as a geological formation that can store and transmit groundwater. This water is located beneath the Earth's surface and is essential for various environmental and human uses, such as drinking water supplies and agriculture. Groundwater, which fills the spaces of rocks and sediment, is typically tapped through wells for extraction.

While surface water refers to water found in rivers, lakes, and streams, and rainwater pertains to the precipitation that either runs off into surface bodies or infiltrates the ground, these are not what is stored in an aquifer. Saline water, which contains a higher concentration of salt, is generally found in oceans or saltwater aquifers and is not the primary focus when discussing the typical definition of an aquifer. The primary and correct definition in this context is that aquifers are sources of groundwater.