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Virtual Water  

Definition of Virtual Water

"Virtual Water" is the amount of water embodied in the goods a country imports and exports.

Source: Lange and Hassan 2006

The concept of virtual water was first introduced by Tony Allan from King’s College in London in the early 1990's. It took nearly a decade for policy makers and academics to recognise its importance; it was first discussed internationally in 2002 in Delft and then at the Third World Water Forum in Japan in March 2003. The concept continues to be debated world-wide.

When it comes to agriculture and virtual water, a distinction is often made between “green virtual water” (referring to rainfed crops) and “blue virtual water” (referring to largely irrigated crops). While green virtual water and its trade do not significantly affect a nation’s water accounts, trade in blue virtual water (or better: in commodities which have been produced using large amounts of irrigation water) may have impacts on a country’s water and even food self-sufficiency.

The concept of virtual water trade and water footprints of SADC countries is further explored in the Virtual Water interactive component on the right side of this page.

Virtual water considers all the water consumed during the life cycle.
Source: Tump 2005
( click to enlarge )

Trade in Water and Virtual Water

Transfer of water between countries via large transfer schemes has numerous drawbacks including high construction and operational costs, loss of water through evapotranspiration in semi-arid regions, and environmental consequences including the potential for the transfer of alien invasive species between countries (particularly aquatic weeds and fish species) (Earle and Turton 2003). Furthermore, political insecurity can arise when a water-scarce country depends on a water-abundant country for critical water supply because if there is conflict between the countries the flow of water can be stopped. Conversely, when the water-abundant country depends on the water-scarce country for its export revenue the importing country has a certain amount of sway over the exporting country.

Arguably, a better alternative to large transfer schemes is trade in virtual water. Trading water-intensive products from water-abundant countries to water-scarce countries provides the same benefit without the drawbacks of large transfer schemes (Earle and Turton 2003). Essentially, if a country imports goods that would otherwise use a lot of its scarce water to produce, the demand on its own water supplies is lessened.

In this respect, products are said to "contain" virtual water—the water used in their creation (Allan 1998). For example the production of 1 kg of grain requires 1 000 to 2 000 kg ( 1 to 2 m³) of water, and 1 kg of beef requires much more - an average of 16 000 kg. Virtual water quantification is not restricted to growing crops or livestock; a 32-megabyte computer chip that weighs 2 g requires an estimated 32 kg of water to manufacture (Williams et al.2002; Hoekstra 2003).

Water Footprint

The Water footprint concept was first introduced by Hoekstra in 2002 and it takes into account the water needed to create a product or commodity (Kort 2010). In this regard the definition is similar to the virtual water content; however, the water footprint can be applied more broadly to the water consumed by people or businesses, and it has dimensions of location and time associated with it. The water footprint considers where the water has come from, when it was used, and more recently has started to also differentiate between the kinds of water used (green, blue or grey water) (Water Footprint Network 2010).

To calculate your water footprint visit the Water Footprint Network page.




Explore the sub-basins of the Kunene River

Video Interviews about the integrated and transboundary management of the Kunene River basin

View information on the dams and weirs of the Kunene Basin

Examine the virtual water trade and water footprints of SADC countries

Explore how hydroelectric dams work