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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.
Water resources are natural resources of water that are potentially useful for humans, for example as a source of drinking water supply or irrigation water. These resources can be either freshwater from natural sources, or water produced artificially from other sources, such as from reclaimed water or desalinated water (). 97% of the water on Earth is salt water and only three percent is fresh ...
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. Fresh water can easily become polluted by human activities or due to naturally occurring processes, such as erosion.
Out of all the water on Earth, saline water in oceans, seas and saline groundwater make up about 97% of it. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers, ice and snow, 0.5–0.75% as fresh groundwater and soil moisture, and less than 0.01% of it as surface water in lakes, swamps and rivers.
The Guarani Aquifer, located beneath the surface of Argentina, Brazil, Paraguay, and Uruguay, is one of the world's largest aquifer systems and is an important source of fresh water. [28] Named after the Guarani people , it covers 1,200,000 km 2 (460,000 sq mi), with a volume of about 40,000 km 3 (9,600 cu mi), a thickness of between 50 and 800 ...
The source of the Blue Nile. 45: Amadjuak Canada: Fresh 3,115 km 2 1,203 sq mi 74 km 3 18 cu mi In geological terms, a "young" lake (approximately 4,500 years old). Second largest on Baffin Island, third largest in Nunavut. 46: Melville Canada: Saline 1.95% (approx. average of surface and bottom water) 3,069 km 2 1,185 sq mi 140 km 87 mi 256 m ...
In 1960, the Aral Sea was the world's twelfth-largest known lake by volume, at 1,100 km 3 (260 cu mi). However, by 2007 it had shrunk to 10% of its original volume and was divided into three lakes, none of which are large enough to appear on this list.
The difference between precipitation and evaporation from the land surface (119,000 − 74,200 = 44,800 km 3 /year) represents the total runoff of the Earth's rivers (42,700 km 3 /year) and direct groundwater runoff to the ocean (2100 km 3 /year). These are the principal sources of fresh water to support life necessities and man's economic ...