• Liquid water covers 70% of Earth's surface
• A total volume of 1.459*10^6 km^3 (or 10^18 kg) occurs as water, ice, and water vapor
• 96% of Earth's water is seawater, 4% is on continents (3% as ice), ~0.001% occurs as vapor atmosphere (B&B Table 1)

Fluxes (B&B Fig. 1) of evaporation/precipitation (0.505*10^6 km^3/yr) necessarily balance globally but not locally - evap>ppt over oceans and vice versa

Sources of terrestrial water: meteoritic influx (early accretion of carbonaceous chondrites), outgassing of the planetary interior (subduction recycling), ongoing cometary influx

Distribution of surface water varied widely with time depending on climate change - during glacial periods much more water occurred as ice caps and glaciers on the continents than at present, whereas during warmer periods practically all the continents were ice-free; during the last Pleistocene glacial maximum (18000 yrs BP), sea level was lower by 130 m and the continent water reservoir was about double that at present (~90*10^6 km^3)

Source: Berner EK & Berner RA (1996) Global Environment: Water, Air, and Geochemical Cycles. Prentice Hall

Source: W.L. Graf (1985) The Colorado River, Resource Publications in Geography, Association of American Geographers, Washington, D.C.

Additional References:

• Charles Bowden (1972) Killing the Hidden Waters. Univ. Texas Press, Austin.
• Sandra Postel (1997) Last Oasis: facing water scarcity. W.W. Norton, New York.