Final answer:
Groundwater is the fresh water found below Earth's surface, occupying the space between rocks and soil in the saturated zone. It provides a significant source of water for various uses, influenced by the porosity and permeability of subsurface materials, and is vital for maintaining the balance of ecosystems.
Step-by-step explanation:
The water beneath the surface of the land that fills the spaces and cavities between rocks and soil is known as groundwater. Groundwater is a crucial part of the Earth's natural water cycle and acts as a vast reservoir of fresh water. It is found in the saturated zone where all the pore spaces in rock and soil are completely filled with water, below the water table, which separates this zone from the above unsaturated zone where pore spaces contain both air and water.
Groundwater exists because of rainfall or snowmelt that infiltrates the ground, moving downwards until it reaches the saturated zone. This underground water can persist for millennia in some cases, and it provides a critical source of fresh water for drinking and irrigation through aquifers. It can also emerge as springs or contribute to rivers and lakes, thereby maintaining surface water levels.
Properties like porosity and permeability are vital in determining how water is stored and moves through subterranean layers. Porosity indicates the amount of open space within the rock, and permeability refers to the rock's capacity to transmit water. Groundwater may also be subject to depletion if the aquifer's water is utilized faster than it is replenished.