The concept of virtual water is important because it enables us to understand why we enjoy the illusion of water and food security despite strong evidence that the water resources available to sustain our national economies are inadequate.
What is virtual water? Virtual water is the water embodied in the production of food and fiber and non-food commodities, including energy. For example, it requires about 1300 tons (cubic meters) of water to produce a ton of wheat and 16000 tons (cubic meters) of water to produce a ton of beef. Thus, someone who eats a lot of beef can consume as much as five cubic meters of embodied water daily, whereas a vegetarian will consume only about 2.5 cubic meters. Production of a cotton T-shirt weighing about 250 grams requires about 2.7 cubic meters of water.
Hoekstra and Mekonnen estimated that the global annual average water footprint of humanity was about 9,087 billion m3/year. This is a tiny proportion of global blue and green water and approximates the blue water flow of the Amazon, the world’s largest river. But it is the volume of water our rainfed farmers and irrigators have been able to use in the farmland they have converted from natural vegetation. Agricultural production accounts for about 92 percent of global water consumption, industry accounts for about 4.4 percent and household water consumption about 3.6 percent. They also estimated that the total volume of international virtual water “flows” related to trade in agricultural and industrial products was 2,320 billion m3/year.
The concept of virtual water—the water embodied in food and non-food commodities—helps explain why our unsustainable political economies of food-water resources exist. More importantly the concept explains why the existence of the dysfunctional food system can be so effectively backgrounded politically.