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Environment Magazine September/October 2008


April 2007

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Bytes of Note: Navigating Virtual Water

It is difficult to comprehend the amount of natural resources used to produce the goods and services we consume. As individuals, therefore, we have little basis to make rational, conservation-minded decisions about our consumption patterns. Every day we make a multitude of decisions that place demands on natural systems: paper or plastic, coffee or tea, oatmeal or corn flakes, corn-derived ethanol or gasoline. Assuming we could instantly alter our preferences to pick the option with the least environmental consequence, we still wouldn’t know the correct answers.

In response to this need, researchers have been hard at work estimating so-called “ecological footprints.” The most prominent examples are based on the work of Mathis Wackernagel and built upon by many others. Wackernagel defines ecological footprint as the “amount of renewable and non-renewable ecologically productive land area required to support the resource demands and absorb the wastes of a given population or specific activities.” This is a useful concept, but what about ecological services other than those provided by the land? What about those that water resources provide, for example?

In their 27 June 2002 Proceedings of the National Academy of Sciences article, Wackernagel and colleagues acknowledged that their footprint computation does not adequately address freshwater use. However, a new community of researchers has begun tracing consumption back to freshwater requirements—a concept known as “virtual water.” The water footprint is too new and not really mature enough to consider a formal integration with the land-based footprints, but it is useful on its own terms. A good introduction to the concept can be found in an article by water management professor Arjen Hoekstra, “Virtual Water Trade Between Nations: A Global Mechanism Affecting Regional Water Systems”; the Water Footprint Network’s site serves as the principal community portal. At the entrance to this portal, we learn that:

• The production of one kilogram of beef requires 16 thousand litres of water.
• To produce one cup of coffee we need 140 litres of water.
• The water footprint of China is about 700 cubic meter per year per capita. Only about 7% of the Chinese water footprint falls outside China.
• Japan, with a footprint of 1150 cubic meter per year per capita, has about 65% of its total water footprint outside the borders of the country.
• The USA water footprint is 2500 cubic meter per year per capita.

The network also provides details on such estimates with such documents as a 2006 Water Resources Management article, “Water Footprints of Nations: Water Use by People as a Function of Their Consumption Pattern,” and the first and second volumes of the UNESCO-IHE Institute for Water Education report Water Footprints of Nations.

The World Water Council, host of the annual World Water Forum, maintains a related virtual water portal with a focus on meeting summaries.

In addition, the Virtual Water Trade Research Programme, which is sponsored by the UNESCO-IHE Institute for Water Education, provides several useful publications.

THOMAS M. PARRIS is a research scientist at and director of the New England offices of ISCIENCES, LLC.

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