The concept of “virtual water” was developed by Professor J.A. Allan of King’s College (London University) and the School of Oriental and African Studies. Allan used it to support his argument that Middle Eastern countries could save their scarce water resources by relying more on food imports. The idea was sufficiently novel for Allan to be awarded the 2008 Stockholm Water Prize.
In Allan’s words, “The water is said to be virtual because once the wheat is grown, the real water used to grow it is no longer actually contained in the wheat. The concept of virtual water helps us realize how much water is needed to produce different goods and services. In semi-arid and arid areas, knowing the virtual water value of a good or service can be useful towards determining how best to use the scarce water available.”
As one example, producing a single kilogram of wheat requires (on average) around 1.5 cubic meters of water, with the precise volume depending on climatic conditions and farming techniques. The amount of water required to grow or make a product is known as the “water footprint” of the product.
Hoekstra and Chapagain have defined the virtual-water content of a product, commodity, good or service, as “the volume of freshwater used to produce the product, measured at the place where the product was actually produced”. The virtual water content is the sum of the water used in the various steps of the production chain.
Additional examples, showing the water footprint of producing one kilogram of:
- biodiesel from soya – 11.4 cubic meters
- beef – 15.4 cubic meters
- butter – 5.5 cubic meters
- chocolate – 17.0 cubic meters
- pasta – 1.85 cubic meters
- sugar (from cane) – 0.2 cubic meters
While the idea of virtual water has attracted some attention, its methodology is contested, and its quantification is not yet sufficiently precise to offer much potential for policy decisions.
Imports and exports of virtual water represent the “hidden” flows of water involved when food and other commodities are traded from one place to another. The map below (from Hoekstra and Mekonnen, 2012) shows the net imports (imports minus exports) of virtual water for different countries for the decade 1996-2005. Note that only the major flows are shown.
In North America, both the USA and Canada have a significant positive virtual water balance (i.e. they are major exporters of virtual water), whereas Mexico has a significant negative water balance, and is clearly one of the world’s largest importers of virtual water.
As Allan’s original work suggests, this is not necessarily bad news since it may imply that Mexico is currently using less of its own (limited) water resources than it might otherwise have to. In other words, Mexico’s virtual water imports may be delaying the inevitable crunch time when water usage becomes a critical limiting factor in the nation’s development.
Source of map
A.Y. Hoekstra and M.M. Mekonnen. 2012. The water footprint of humanity. Proc. Nat. Academy of Sciences, 109, 3232-7. Map was reproduced in “Spotlight on virtual water” by Stuart N. Lane in Geography, vol 99-1, Spring 2014, 51-3.
- Mexico’s freshwater aquifers: undervalued and overexploited (Nov 2011)
- How can Mexico City find sufficient water? (May 2013)