Figure 3.3 Past and projected U.S. oil imports in millions of barrels per day, 1950-2015. SOURCE: PCAST, 1997, pp. 1-8.

(97 percent) consists of the salt water of the oceans. Less than 1 percent is available for the world's biota, animals, and humans because 80 percent of freshwater is locked up in ice caps and glaciers. Nonetheless, the total amount of freshwater is more than enough to meet the world's needs now and in the future. The problem is that this global abundance is unevenly distributed among countries and regions, and local stocks or supplies are finite.

Water is a key determinant of population growth and distribution, economic development, social and political organization, and the quality of life. It is also a cause of war and a catalyst for peace. Thus, information and knowledge about this renewable resource are essential to human welfare everywhere. Because water resource issues in the United States and elsewhere are unlikely to diminish in upcoming decades, it appears probable that USGS information on streamflows and water use, regional water resource studies, and hydrologic research will be more important in the future than in the present.

Although per capita use of water in the United States and worldwide has declined since the mid-1980s (Gaelic, 1998), there is no reason to be