Food: Biological productivity and the
provision of food are maintained by an intact
river system. Intensive agricultural
production often relies on extensive networks
of irrigation, bringing water to crops that
otherwise couldn't grow in those locations.
It takes at least 1000 tons of water to
produce one ton of grain, thus populated
regions of the world with water
shortages-North Africa and the Middle
East-were also the fastest growing grain
import markets in the 1990s (FAO,
1979). The world's food supplies hinge on
adequate and available freshwater.