Rivers form a hydrological mosaic, with an estimated 263 international river basins covering 45.3% of the land surface area of the earth, excluding Antarctica. This graphic shows the locations of 26 of the world's major river basins. A basin is defined as the land area (watershed) where all surface water drains to a certain river.

Glaciers and ice caps cover about 10% of the world’s landmass. These are concentrated in Greenland and Antarctica and contain 70% of the world’s freshwater. Unfortunately, most of these resources are located far from human habitation and are not readily accessible for human use. According to the United States Geological Survey (USGS), 96% of the world’s frozen freshwater is at the South and North Poles, with the remaining 4% spread over 550,000 k...