Groundwater is water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 located beneath the ground surface in soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...

 spaces and in the fracture
A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...

s of rock formation
Rock formation
This is a list of rock formations that include isolated, scenic, or spectacular surface rock outcrops. These formations are usually the result of weathering and erosion sculpting the existing rock...

s. A unit of rock or an unconsolidated deposit is called an aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...

 when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...

. Groundwater is recharged from, and eventually flows to, the surface naturally; natural discharge often occurs at spring
Spring (hydrosphere)
A spring—also known as a rising or resurgence—is a component of the hydrosphere. Specifically, it is any natural situation where water flows to the surface of the earth from underground...

s and seeps
Seep (hydrology)
A Seep is a moist or wet place where water, usually groundwater, reaches the earth's surface from an underground aquifer.-Description:Seeps are usually not of sufficient volume to be flowing beyond their above-ground location. They are part of the limnology-geomorphology system...

, and can form oases
In geography, an oasis or cienega is an isolated area of vegetation in a desert, typically surrounding a spring or similar water source...

 or wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....