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The '''virtual water''' content of a product is the volume of water used to produce the product, measured at the place where the product was actually produced (''production site specific definition''). The virtual water content of a product can also be defined as the volume of water that would have been required to produce the product in the place where the product is consumed (''consumption site specific definition'').
The adjective ‘virtual’ refers to the fact that most of the water used to produce a product is in the end not contained in the product. The real water content of products is generally negligible if compared to the virtual water content.
== Virtual Water Concepts ==
People do not only consume water when they drink it or take a shower. In 1993, Professor [[John Anthony Allan]]* from King’s College London and the School of Oriental and African Studies, 71, strikingly demonstrated this by introducing the “virtual water” concept, which measures how water is embedded in the production and trade of food and consumer products. Behind that morning cup of coffee are 140 litres of water used to grow, produce, package and ship the beans. That is roughly the same amount of water used by an average person daily in England for drinking and household needs. The ubiquitous hamburger needs an estimated 2,400 litres of water. Per capita, Americans consume around 6,800 litres of virtual water every day, over triple that of a Chinese person.
Virtual water has major impacts on global trade policy and research, especially in water-scarce regions, and has redefined discourse in water policy and management. By explaining how and why nations such as the US, Argentina and Brazil ‘export’ billions of litres of water each year, while others like Japan, Egypt and Italy ‘import’ billions, the virtual water concept has opened the door to more productive water use. National, regional and global water and food security, for example, can be enhanced when water intensive commodities are traded from places where they are economically viable to produce to places where they are not. While studying water scarcity in the Middle East, Professor Allan developed the theory of using virtual water import, via food, as an alternative water “source” to reduce pressure on the scarcely available domestic water resources there and in other water-short regions.
(* [[John Anthony Allan]] has been named the 2008 Stockholm Water Prize Laureate. Professor Allan pioneered the development of key concepts in the understanding and communication of water issues and how they are linked to agriculture, climate change, economics and politics.)
=== Virtual water export ===
The virtual water export of a country or region is the volume of virtual water associated with the export of goods or services from the country or region. It is the total volume of water required to produce the products for export.
=== Virtual water import ===
The virtual water import of a country or region is the volume of virtual water associated with the import of goods or services into the country or region. It is the total volume of water required (in the export countries) to produce the products for import. Viewed from the perspective of the importing country, this water can be seen as an additional source of water that comes on top of the domestically available water resources.
=== Virtual water flow ===
The virtual water flow between two nations or regions is the volume of virtual water that is being transferred from one place to another as a result of product trade.
=== Virtual water balance ===
The virtual water balance of a country over a certain time period is defined as the net import of virtual water over this period, which is equal to the gross import of virtual water minus the gross export. A positive virtual water balance implies net inflow of virtual water to the country from other countries. A negative balance means net outflow of virtual water.
=== National water saving ===
A nation can save its domestic water resources by importing a water-intensive product rather than produce it domestically.
=== Global water saving ===
International trade can save water globally if a water-intensive commodity is traded from an area where it is produced with high water productivity (resulting in products with low virtual water content) to an area with lower water productivity.
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== Water Footprint ==
The [[water footprint]] concept is closely linked to the virtual water concept. Virtual water
is defined as the volume of water required to produce a commodity or service. Virtual water imports are used (coming along with food imports) as a tool to release the pressure on the scarcely available domestic water resources. Virtual water import thus becomes an alternative water source, next to endogenous water sources. Imported virtual water has therefore also been called ‘exogenous water’.
When assessing the water footprint of a nation, it is essential to quantify the flows of virtual
water leaving and entering the country. If one takes the use of domestic water resources as
a starting point for the assessment of a nation’s water footprint, one should subtract the
virtual water flows that leave the country and add the virtual water flows that enter the country.
To calcuate your individual or national water footprint, go to [http://www.waterfootprint.org The Water Footprint website]
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== Some facts and figures ==
*The per capita consumption of virtual water contained in our diets varies according to the type of diet, from 1 m3/day for a survival diet, to 2.6 m3/day for a vegetarian diet and over 5 m3 for a United States style meat based diet.
* In general, livestock products have a higher virtual water content than crop products. For example, the global average virtual water content of maize, wheat and rice (husked) is 900, 1300 and 3000m3/ton respectively, whereas the virtual water content of chicken meat, pork and beef is 3900, 4900 and 15500m3/ton respectively.
* Globally, water is saved if agricultural products are traded from regions with high water productivity to those with low water productivity. At present, if importing countries produced all imported agricultural products domestically, they would require 1,600 Km3 of water per year; however, the products are being produced with only 1.200 Km3/yr in the exporting countries, saving global water resources by roughly 400 billion m3/yr.
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== Further Readings - References - Links ==
[[Did you know?.. Facts and Figures around Water]]
[http://www.unesco.org/water/ UNESCO-Water Portal]
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== Source(s) ==
[http://www.waterfootprint.org The Water Footprint website]
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[[Category:Virtual water]]
[[Category:Global]]
[[Category:Water Footprint]]
[[Category:Efficiency]]
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