Virtual water trade and world water resources.

Global virtual water trade was quantitatively estimated and evaluated. The basic idea of how to estimate unit requirement of water resources to produce each commodity is introduced and values for major agricultural and stock products are presented. The concept of virtual water and the quantitative estimates can help in assessing a more realistic water scarcity index in each country, projecting future water demand for food supply, increasing public awareness on water, and identifying the processes wasting water in the production. Really required water in exporting countries is generally smaller than virtually required water in importing countries, reflecting the comparative advantage of water use efficiency, and it is estimated to be 680 km3/y for 2000. On the contrary the virtually required water for the same year is estimated to be 1,130 km3/y, and the difference of 450 km3/y is virtually saved by global trade. However, solely virtual water should not be used for any decision making since the idea of virtual water implies only the usage and influence of water and no concerns on social, cultural, and environmental implications. Virtual water trade also does not consider other limiting factors than water.