An aquifer is an underground layer of rock, sand, or gravel that contains groundwater.
Aquifers are layers of rock that hold a lot of water and allow it to circulate.
Your question - while a good one - is slightly ambiguous, it could be several different things, but I think what you are asking about is what is called an "aquifer".
soil?
condensation
Fracking is the practice of injecting water and chemicals into underground rock.
Groundwater. (:
groundwater
artesian basin
Water collects underground by slowly seeping through the ground until it reaches hollows of the earth where it can collect. These are often called aquifers and are major sources of water for cities.
1.Rain 2.Rain collects underground. 3.Rain seeps underground. 4.Rain is underground.
Underground water is called underground water, because it is "underground" not because it is fresh or salt. You can have underground salt water reservoirs just like you can have fresh water ones.
Underground water is called underground water, because it is "underground" not because it is fresh or salt. You can have underground salt water reservoirs just like you can have fresh water ones.
condensation
Natural underground reserves of fresh water are generally called aquifers.
an underground layer of rock that can hold water is an aquifer.
The water on the surface of the ground, or water that is not ground water (water underground) that collects in lakes, rivers, streams or oceans. See the related links for more information.
Underground springs.
bilge bilge
magma chamber
ground water