Virtual water refers to the water required in the production of a good or service. For instance, it takes more or less 1,200 cubic meters of water to produce one metric tonne of wheat (depending on where and how it is grown). The water is said to be virtual because once the wheat is grown, the real water used to grow it is no longer actually contained in the wheat. The concept of virtual water helps us realize how much water is needed to produce different goods and services. In semi-arid and arid areas, knowing the virtual water value of a good or service can be useful towards determining how best to use the scarce water available.

"Virtual water refers to the water required in the production of a good or service. The water is said to be virtual because once the good is grown, the real water used to grow it is no longer actually contained in the good. The concept of virtual water helps us realize how much water is needed to produce different goods and services. In semi-arid and arid areas, knowing the virtual water value of a good or service can be useful towards determining how best to use the scarce water available.” (Tony Allen, Nov 2005)

Virtual water trade refers to the idea that when goods and services are exchanged, so is virtual water. When a country imports one tonne of wheat instead of producing it domestically, it is saving about 1,200 cubic meters of real indigenous water. If this country is water-scarce, the water that is 'saved' can be used towards other ends. If the exporting country is water-scarce, however, it has exported 1,200 cubic meters of virtual water since the real water used to grow the wheat will no longer be available for other purposes.

Daniel Zimmer, Director of the World Water Council, in his presentation at the session on "virtual water trade and geopolitics" at the 2003 World Water Forum in Kyoto:

"When you consume one kilogram of grain, you are also consuming 1,000 litres of water needed to grow that grain; when you consume a kilogram of beef you are consuming 13,000 litres of water needed to produce that amount of meat, and this is the hidden or virtual water.140 litres of water is used to produce one cup of coffee. It is this unconscious behaviour that causes humans to consume so much water. ^*

"The contrast in water use can be noticed between continents. In Asia, people consume an average of 1,400 litres of virtual water a day, while in Europe and North America, people consume about 4,000 litres. About 70 per cent of all water used by humans goes into food production. ^*

"Among the biggest net exporter countries of virtual water are the U.S., Canada, Thailand, Argentina, India, Vietnam, France and Brazil. Some of the largest net import countries are Sri Lanka, Japan, the Netherlands, South Korea, China, Spain, Egypt, Germany and Italy."

Water-scarce countries like Israel discourage the export of oranges (relatively heavy water guzzlers) precisely to prevent large quantities of water being exported to different parts of the world. Eau virtuelle | 仮想水

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