Groundwater is potable water which is stored underground. It can be confined, which means that a deposit of water is surrounded by nonpermeable rock, or unconfined, in which case it is surrounded by permeable rock, gravel, soil, and other materials. Around 20% of the world's freshwater is groundwater, and groundwater makes up a significant portion of the potable water consumed worldwide, with up to 50% of some populations relying on groundwater for drinking, bathing, industrial production, and a variety of other tasks.
A number of things can lead to the development of a groundwater formation. Rainfall, for example, drains into the ground and into deposits of groundwater, and runoff from rivers, streams, and lakes also winds up in the world's groundwater. Groundwater levels are also supplemented by snow melt and melting glaciers, and the supply may be seasonal, depending on high rainfall and snow melt to supply groundwater in the spring, with supplies which dwindle in the late summer and fall.
When a deposit of groundwater can be used sustainably as a water source by humans, it is known as an aquifer. Many people try to seek out contained aquifers, because the quality of the groundwater tends to be better when it is contained. Contained aquifers are at less risk of pollution, making the water safer to drink. In an unconfined aquifer, water can be tainted with chemicals, biological agents, feces, and other materials which are not desirable in drinking water.
One of the most common ways to access a deposit of groundwater is a well. Wells are drilled down into deposits of groundwater and pressurized so that the water bubbles to the surface, allowing people to use it. People can also dip buckets into wells to collect the water, as has been done historically. It is also possible to access groundwater through springs, which periodically bubble up with fresh groundwater. Historically, settlements have often been constructed around springs, to save the cost of sinking a well to supply a community.
Sometimes, a water source dries up. This happens when the aquifer is so depleted that it cannot provide water anymore. Sometimes, drilling deeper can solve the problem, by accessing the bottom of the aquifer. In other instances, a well or spring may refill itself at a later juncture, after the aquifer has had a chance to recover. Abandoned wells are viewed as a safety risk in some areas, since the lack of maintenance can result in an uncovered well which people or animals could fall into.
