Groundwater is the 2nd largest available reservoir of fresh water. The diagram below shows that of the world's fresh water, the majority is locked away as ice in the polar ice caps, continental ice sheets and glaciers. Surface waters such as rivers and lakes only accounts for less that 1% of the worlds fresh water reserves whereas groundwater accounts for 12% of the worlds freshwater resources.

For a detailed explanation of where Earth's water is, look at the data table below. Notice how of the world's total water supply of about 326 million cubic miles of water, over 96 percent is saline. And, of the total freshwater, over 68 percent is locked up in ice and glaciers. Another 30 percent of freshwater is in the ground. Surface-water sources, such as rivers, only constitute about 300 cubic miles (about 1/10,000 th of one percent of total water).

World Water Distribution
Water sourceWater volume, in cubic milesWater volume, in cubic kilometersPercent of fresh waterPercent of total water
Oceans, Seas, & Bays321,000,0001,338,000,000--96.5
Ice caps, Glaciers, & Permanent Snow5,773,00024,064,00068.71.74
Soil Moisture3,95916,5000.050.001
Ground Ice & Permafrost71,970300,0000.860.022
Swamp Water2,75211,4700.030.0008
Biological Water2691,1200.0030.0001
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.