Giulio Boccaletti in Aeon:
A great river encircles the world. It rises in the heartland of the United States and carries more water than the Mississippi and Yangtze rivers combined. One branch, its oldest, streams over the Atlantic, heading for Europe and the Middle East. Another crosses the Pacific, flowing towards China. Countless tributaries join along the way, draining the plains and forests of Latin America, Europe and Asia.
You probably have never heard of such a river, even though almost all of us draw from it. You cannot fish in it, float on it, drink from it. If you were to look, you would not find it: it is invisible. Yet there is no doubt that it flows.
The river starts anywhere water feeds agriculture. But from there, physical water vanishes, replaced by a flow of crops that carry only the memory of the water used to produce them. Crops then travel along the shipping lanes of the global trade system, eventually displacing the water that would have otherwise been used to grow them locally. Thus, water flows from source to destination ‘embedded’ in its products. It is a flow of ‘virtual water’, an idea first developed in the 1980s by the late geographer Tony Allan.