Water is evaporated from the oceans and the land and returned as rain or snow, forming the hydrologic cycle.

One estimate of global water distribution
Water sourceWater volume,
in cubic miles
Water volume,
in cubic kilometers
Percent of total waterPercent of total freshwater
Fresh ground water2,526,00010,530,0000.8%30.1%
Ground water5,614,00023,400,0001.7%--
Total global water332,500,0001,386,000,000----
Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823.
WaterPatterns of runoff

Geophysics concepts

Lutgens & Tarbuck
Ch 9
HyperPhysicsR Nave
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