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Home page > Research Topics > Trade Policy > Agriculture > World Water GAP

World Water GAP, A Global Approach Program

Our transferable hydrologic capital


Virtual Water is the volume of water needed to produce a specific quantity of good or services. For agricultural products, it is calculated on the basis of a country’s specific crop water requirements estimated in cubic meter per ton of products (< see chart for comprehensive calculation >). This water is said to be virtual as it is not anymore present in the good or service. For instance, an egg needs 135 liters of water to be produced a 150 grams hamburger needs 2400 liters of water to be produced, a cotton tee shirt and a pair of (bovine) leather shoes respectively 2000 and 8000 liters.

These observations reframe our perception of water in a totally different dimension.

The importance of relativity… once and for all

The importance of absolute terms gives us goals in terms of increasing water productivity (i.e. is the amount of water for a specific amount of production or crop water requirements).

The analysis must also consider the comparison between countries and the origin of the production of goods or services. Depending on climatic, land, geographical and hydrological characteristics, a country uses more or less water to produce certain goods. Put differently, countries have specific water productivities for each of its agricultural production:

Consequently, a country can have an advantage over others to produce certain products in terms of water content as a production factor. This does not mean that Morocco should stop growing wheat or maize and import them from other countries. Firstly because countries have the right to implement national food security policies, secondly because what matters is the relative advantage of producing a good so that a country can always gain from producing a basket of good depending on its relative advantage.

Water that crosses borders

Water is bulky – of course, water cannot be transported as easily as goods can be. It is far more interesting to export virtual water embedded into the good.

Water crosses borders – it does so in a virtual way through international trade. A virtual water map can then be drawn as a subsequent layer of international trade flows. Right after NAFTA (North American Free Trade Agreement) was signed, Canada began to have concerns about its water falling into the agreement’s constraint. A text from the NAFTA statement of September 1993 states that:

"Unless water, in any form, has entered into commerce and become a good or product, it is not covered by the provisions of any trade agreement including the NAFTA. And nothing in the NAFTA would oblige any NAFTA Party to either exploit its water for commercial use, or to begin exporting water in any form."

Let’s recall that the concept of virtual water was put forward at first in 1994. Mostly addressing the question of water bottles, did Canada knew at the time the amount of Canadian virtual water that would cross its border through agricultural trade? Last evaluations show that nearly 13% of all water consumed for agriculture globally is being exported as virtual water.

On going research

Water GAP will try to contribute to the debate on whether international trade can save water or not, by:

  • determining the impact of selected agricultural trade policies on virtual water flows and on how trade policy can affect water depletion or water savings;
  • determining how water can be a side-factor for agricultural trade negotiations in particular in the context of World Trade Organization or regional trade agreements;
  • determining the impact of agricultural products subsidies and water uses subsidies on virtual water flows.


Le Vernoy, Alexandre, "Water and Trade in Agriculture: Investigating Virtual Water Hypothesis in the Euro-Mediterranean Region", Policy brief. May 2006. English, Français.

Le Vernoy, Alexandre, "L’eau, une chance pour l’agriculture française: La libéralisation des échanges agricoles pourrait donner l’avantage aux pays utilisant plus parcimonieusement le précieux liquide", Le Monde, January 2006



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