Expert Commentary

The water footprint of humanity

2012 study in the Proceedings of the National Academy of Sciences on the total amount of water utilized by individuals and societies globally.

As the world’s population continues to grow, measuring countries’ water consumption patterns is crucial for understanding looming resource challenges and making effective international policy decisions.

A 2012 study from the University of Twente (The Netherlands) published in the Proceedings of the National Academy of Sciences, “The Water Footprint of Humanity,” quantifies water consumption and pollution for all countries, including water resources used as part of international trade, to establish a full picture of global water use. The study employs a broad “water footprint” (WF) measurement, which encompasses water withdrawals within a country’s territory, use of rainwater, water used for “waste assimilation,” as well as water used in the making of imported goods.

The study’s findings include:

  • From 1996 to 2005, annual global average WF was 9,087 gm3 per year (a gigameter is 1 billion meters.) The countries with the highest WF within their territories were China (1,207 gm3/y), India (1,182 gm3/y) and the United States (1,053 gm3/y); together, they made up 38% of the world’s total WF.
  • Of global WF due to industrial production, China represented 22% and the United States 18% — the “largest WFs in their territory related to industrial production.”
  • “The WF of the global average consumer was 1,385 m3∕y.The average consumer in the United States has a WF of 2,842 m3/y, whereas the average citizens in China and India have WFs of 1,071 and 1,089 m3/y, respectively.” (A cubic meter is approximately 264 gallons, meaning that the average daily consumption globally for an individual is 1,002 gallons. For U.S. residents, the figure is 2,057 gallons a day.)
  • Of the 9,087 gm3/y global average for water used in human activities, 74% typically involve rainwater, 11% ground or surface water and 15% volumes of water polluted.
  • Agricultural uses constituted the vast majority (92%) of global WF; industrial uses make up 4.4% and domestic water supply 3.6%. Moreover, “at the level of product categories, cereals consumption contribute the largest share to the global WF (27%), followed by meat (22%) and milk products (7%).”
  • Some 76% of “virtual” international water flows — calculated by multiplying the volume of trade in a commodity by the WF per ton of that commodity in the exporting country — are accounted for by international trade in crops and derived crop products. Industrial products have a 12% share of global virtual water flows. Export goods were found to have a stronger correlation with “water consumption from and pollution of surface and groundwater than non-export goods.”
  • Roughly half of the global virtual flows are accounted for by countries that also report water scarcity, including the United States, Pakistan, India, Australia, Uzbekistan, China and Turkey. This raises the question whether decisions to export water-intensive products resulted in the most efficient use of water sources for domestic populations.

The study concludes that approximately 20% of global water footprint from 1996 to 2005 was intended for export. “The relatively large volume of international virtual water flows and the associated external water dependencies strengthen the argument to put the issue of water scarcity in a global context,” the report states. “For governments in water-scarce countries such as in North Africa and the Middle East, it is crucial to recognize the dependency on external water resources and to develop foreign and trade policies such that they ensure a sustainable and secure import of water-intensive commodities that cannot be grown domestically.”

Tags: water, agriculture, development, China, Asia

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