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Groundwater is fresh water located in the subsurface pore space of soil and rocks.It is also water that is flowing within aquifers below the water table.Sometimes it is useful to make a distinction between groundwater that is closely associated with surface water, and deep groundwater in an aquifer (called "fossil water" if it infiltrated into the ground millennia ago [8]).
[9] Fresh water resources are unevenly distributed in terms of space and time and can go from floods to water shortages within months in the same area. In 1998, 76% of the total population had a specific water availability of less than 5.0 thousand m 3 per year per capita.
Most water in Earth's atmosphere and crust comes from saline seawater, while fresh water accounts for nearly 1% of the total. The vast bulk of the water on Earth is saline or salt water, with an average salinity of 35‰ (or 3.5%, roughly equivalent to 34 grams of salts in 1 kg of seawater), though this varies slightly according to the amount of runoff received from surrounding land.
Fresh water is the water resource that is of the most and immediate use to humans. Fresh water is not always potable water, that is, water safe to drink by humans. Much of the earth's fresh water (on the surface and groundwater) is to a substantial degree unsuitable for human consumption without treatment.
Location Area (km 2) Average depth (km) Image Notes Earth: planet (terrestrial) 1.362 [10] World Ocean: salt water: surface, global 361,300,000 3.68 (max 11.02) commonly divided into five regions 71% of Earth's surface Caspian Sea: salt water surface, Central Asia: 389,000 0.21 (max 1.02) Earth's largest inland body of surface liquid, endorheic
About 97.5% of the water is saline; the remaining 2.5% is fresh water. [ 196 ] [ 197 ] Most fresh water, about 68.7%, is present as ice in ice caps and glaciers . [ 198 ] The remaining 30% is ground water , 1% surface water (covering only 2.8% of Earth's land) [ 199 ] and other small forms of fresh water deposits such as permafrost , water ...
An image shows the comet 67P/Churyumov-Gerasimenko in March 2015. New research from NASA says Jupiter-family comets like this one could have been potential sources of water for early Earth ...
Springs have long been important for humans as a source of fresh water, especially in arid regions which have relatively little annual rainfall. Springs are driven out onto the surface by various natural forces, such as gravity and hydrostatic pressure. A spring produced by the emergence of geothermally heated groundwater is known as a hot spring.