When we manufacture goods, we embed energy in them: that is, their existance means we have already spent a certain amount of energy, no matter what we then do with them.
In a similar way, when we grow crops we are in a sense embedding water within them. If a kilo of wheat takes a thousand liters of water to grow from sowing to harvest, we can, seen from a certain light, think of that kilo of wheat as containing 1,000 liters of water.
When we consider how much water is embedded in the food we transport around the planet, it turns out that there is a massive trade in virtual water. The wetter regions of the world every year ship vast amounts of embedded water to the drier parts of the planet. This has gigantic ecological and geopolitical consequences, and as climate change intensifies, could be a trend which produces great friction.
One helpful concept? Thinking of our water footprints, which, like ecological footprints or carbon footprints, allow us to measure the ways in which our actions echo in the world -- in this case, how what we buy, use and eat influences the amount of water (both immediate and virtual) we consume.
