Water Footprint: One-fifth for export

World trade shifts water needs in producer countries

Cotton is one of the most water-intensive export goods © Kimberly Vardeman / CC-by-sa 2.0
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Every person consumes almost an Olympic swimming pool full of water every year, solely through the consumption of goods: an average of 1, 385 cubic meters of precious water. However, much of this water does not come from the own country. Instead, it is consumed in countries that manufacture products for export. About one fifth of the global water footprint goes back to such export products. As a result, water consumption is shifting to producer countries, Dutch researchers report in the journal Proceedings of the National Academy of Sciences.

As a footprint, the researchers summarize the amount of water that is taken from resources such as rivers, lakes or groundwater and discharged as polluted wastewater again. So far, little attention has been paid to national statistics on water use, which leaves water footprints outside of their own country, say the scientists. This includes, for example, how much water is needed elsewhere to produce the imported products or how much water is polluted there.

"Many producer countries are suffering from water scarcity, raising the question of how sustainable and effective it is to use scarce resources for export, " write Arjen Hoekstra and Mesfin Mekonnen from the University of Twente in Enschede. Accurate mapping of virtual water flows is the first step in weighing this up.

The biggest factor is world trade in agricultural products

According to the researchers, between 1995 and 2005, around 2, 320 billion cubic meters of water were shipped per year with world trade around the world - this corresponds to about one and a half times the amount of water in Lake Ontario. 76 percent of this virtual water trade was due to international trade in agricultural products such as cotton, soybeans and cereals. To produce one kilo of cotton, you need about 15, 000 liters of water, for a kilo of wheat still around 1, 000 liters.

This chart shows the ratio of virtual water import and export through world trade for countries worldwide (green = more export, red = more import) and the main trade flows of agricultural and non-agricultural industrial products between 1996 and 2005. PNAS / Hoekstra, Mekonnen

Among the largest importers of water-consuming products, the researchers rank Germany third after the USA and Japan. Germany imports 125 billion cubic meters of virtual water per year, which is equivalent to around one and a half times Lake Geneva. On the other hand, Germany also exports 64 billion cubic meters of water per year via various products to other countries. display

Water footprint broken down into three components

In their study, the scientists separate three components of the water footprint: The "blue" footprint stands for used ground and surface water, the "green" footprint for rainwater and the "gray" for the amount of water that is polluted. China's water pollution alone accounts for 26 percent of the global gray water footprint, the researchers report.

In all three categories, China, the USA and India are the largest water consumers worldwide. These three countries together account for 38 percent of the global water footprint of humanity. In the US, per capita consumption is also significantly higher at 2, 842 cubic meters per year than in most European countries, the researchers say. This is mainly due to the high beef consumption of Americans. The water footprint for this beef is around 15, 000 cubic meters of water per tonne. (PNAS, 2012; doi: 10.1073 / pnas.1109936109)

(PNAS, 14.02.2012 - NPO)