December 2008, Vol. 20, No.12

Water Volumes

Globalization of Water: Sharing The Planet’s Freshwater Resources

Arjen Y. Hoekstra and Ashok K. Chapagain (2008). Blackwell Publishing, 350 Main St., Malden, MA 02148 USA, 224 pp., $64.95, hard cover, ISBN: 978-1-4051-6335-4.

It is widely accepted today that environmental impact is not to be considered locally but, rather, globally. Nevertheless, water use is still evaluated as direct local (national) consumption of surface water and groundwater (referred to as “blue water” in this book), in some cases also including rainwater (“green water”).

The authors propose to reverse the logic of production volumes to consumption volumes. This implies that the water volume needed to obtain a product is calculated; this is denoted as the “virtual water content” of the product. World trade then can be translated to virtual flows of water — a typical example is a cup of coffee, which requires 140 L of water to produce, not at the place of consumption but in a totally different area of the world. This approach entirely changes all conclusions concerning water stress in the world, dependencies on other countries, and responsibility for water scarcity. This detailed study gives new insights into these mechanisms, leading to a more realistic picture of a country’s water needs. A country may solve a water scarcity problem by importing water-intensive products, such as meat, rice, and wheat. This can be expressed by a nation’s water footprint, to be divided into an internal footprint (extraction and consumption in the country itself) and an external footprint (consumption in the country but production in a different country).

The concepts of virtual water and water footprints are explained well in the first five chapters of the book, which include extensive numerical data and color maps. These data indicate how the global water balance can be improved. Evidently, more detailed studies are needed for specific virtual water flows, as shown in a detailed case study about the water footprints of Morocco and the Netherlands (and virtual water trade between the two). This also can be done within one country, as described in a separate chapter about water transfers in China. Conclusions here are quite remarkable. Real water flows from south to north in China, but the water-scarce north is actually the largest exporter of virtual water.

One also may study specific crops, as was done in this book for coffee and tea, and for cotton. The book contains extensive and detailed tables, with all the data required for an in-depth evaluation. One of the most prominent conclusions is that water consumption on a global scale depends mainly on evaporation rates (for crops) and yield of product; water savings can be obtained when production is localized in the most water-efficient place.

The book concludes with some important remarks on fairness, sustainability, responsibility, and price-setting.


Bart Van der Bruggen is a professor in the Department of Chemical Engineering at the University of Leuven (Belgium).