A water footprint sounds like something you leave on the bathroom floor after a shower. Virtual water, meanwhile, might seem like an ironic postmodern conceit by the late Jean Baudrillard. Yet if environmental campaigners are successful these two ideas could soon become powerful and practical tools in the management of the world's water needs - as potent, perhaps, as the carbon footprint now is in shaping global and governmental consciousness about greenhouse gas emissions.
As WWF's new report on the UK's water usage explains today, virtual water is the volume of water that is required to produce a particular product. A can of fizzy drink might contain 0.35 litres of water, for instance, yet it also requires around 200 litres to grow and process the sugar that goes into it. A pair of leather shoes may contain no water at all, but it requires 8,000 litres to grow the feed, support the cow and then process its skin before you start wearing the shoes. Add all this virtual water together and you have a water footprint for a person, a business, a community or a country.
Start thinking in these terms and two things become obvious. First, that we consume far more water to support our lifestyles than most of us may imagine - a typical British household uses 30 times as much virtual water as the amount it obtains through the taps for washing, cooking or drinking. Second, that when virtual water is taken into account, consumers in developed nations are leaving a large water footprint not just in their own countries but across the globe too. Only 38% of the UK's total footprint, for instance, comes from our own resources. The other 62% comes from other parts of the planet (we are the world's sixth largest net importer of virtual water) . But since water is in many ways a finite and, in some places, a dwindling resource that is also the cause of conflict, this massive import of virtual water too often comes at the expense of people and ecosystems that can ill afford to lose it.
Competition for water takes many forms in many continents. But it cannot be responsible behaviour for consumers in the west to unthinkingly demand water-heavy food imports from countries where resources are under such pressure. In 25 years, the UN reckons, more than half of all Africans will be living in countries suffering such "water stress". Fresh mangetout at such a price is not acceptable.
Happily, some producers and retailers are responding to calls to stop the flow of water from the poor to the rich in their food chains. But individual consumers must act too. All of us need to apply as much rigour to reducing our water footprint as we have begun belatedly to apply to the reduction of our carbon one.