Water Use - Freshwater Availability

Most human and land-based animal and plant activities that use water require freshwater. In the vast majority of cases, saline or salt water cannot be used without treatment. Of the estimated 861 million cubic miles of water on the planet, barely 3% (twenty-six million cubic miles) is freshwater. If this water were distributed over the planet relative to population density and animal and plant needs, it would be more than enough to sustain all life forms on Earth.

Water, however, is not distributed evenly over the planet. Freshwater supplies vary not only from region to region, but from year to year within regions. Within the continental United States, some parts of the country do not have adequate supplies at the same time that other areas may be experiencing floods. For example, in 2001, while rains flooded the Mississippi Valley for weeks, severe drought threatened Florida.

The first human settlements were based on the availability of water. Where water was plentiful, large numbers of people flourished; where water was scarce, small groups eked out a living. Villages and cities thrived in areas of constant water supply. In more arid regions, nomads wandered in search of water. Great nations grew up along the Nile River in Egypt, the Tigris and the Euphrates Rivers in western Asia, the Indus River in India, and the Yellow River in China. Modern societies have more control over the water supply. They have developed technologies that bring water to arid regions and divert water from areas likely to flood. Elaborate irrigation systems have made it possible for cities to exist today in places where one hundred years ago only the hardiest plants and animals could survive. For example, without these water systems, Los Angeles would be a semiarid desert.