Forget carbon: you should be checking your water footprint

Ethical shopping just got harder – but the latest attempt to help conscientious consumers calculate their impact on the environment could do more to preserve scarce resources than all its predecessors.

The concept of water footprints – or "virtual water" – will tell consumers the amount of precious H2O that has been used in the manufacture of products they buy. As with carbon footprints, a "virtual water" figure will indicate the extent to which a particular product has cost the earth. And, as with carbon footprints, the message is clear: less is better.

A new website run by the University of Twente in the Netherlands, waterfootprint.org, gives ethically minded consumers a chance to work out the hidden implications of their shopping habits. Common commodities including groceries, clothes, stationery and electrical goods are evaluated according to a water footprint calculator. In each case, the water footprint covers both the manufacture and transport of the goods.

The results are striking. An apple weighing 100g has a water footprint of 70 litres, while a 125ml cup of coffee has a water footprint twice that size, 140 litres. But the water used in producing wheat or meat is much greater. A single kilogram of barley has a water footprint of 1,300 litres, while the industrial production of a kilogram of beef amasses a water footprint of 15,500 litres.

Poultry, meanwhile, has a smaller water footprint than red meat: producing a kilogram of chicken meat leaves a comparably much smaller water footprint of 3,900 litres.

Academics behind the "virtual water" calculations have also created a worldwide league table for the water footprint of different countries. The US is the biggest offender, with a water footprint of close to 2,500 cubic metres per year per capita, while Italy is a close second. Britain's water footprint is relatively modest at 1,245 cubic metres per year per capita.

The calculations are fiendishly complicated. But if they prove popular, calculations of water footprints could do much more to help minimise the environmental impact of consumption than other, similar schemes.

Over the past year in particular, controversy has surrounded the idea of "food miles", as mounting evidence throws doubt on the idea that locally produced food is better for the environment. Research suggests that many products freighted in from halfway across the globe can leave smaller carbon footprints than carbon intensive production methods closer to home.

Yet for consumers keen to minimise their water wastage, there remains a single, simple mantra to live by: always recycle.

A cotton shirt, for example, has a water footprint of 2,700 litres, tallying up the water evaporated in irrigating and growing the cotton, as well as the water needed to wash away fertilisers. Recycling such products, and thereby minimising fresh production, could make the earth's water resources go much, much further.

"Our research shows that most people aren't aware of how much water they use," a spokesperson from the Consumer Council for Water said yesterday.

Though it covers more than two-thirds of the earth's surface, water has never been more precious. An influential UN report published in 2003 predicted severe water shortages would affect 4 billion people by 2050, adding that 40 per cent of the world's population did not have access to adequate sanitation facilities.

Counting the cost

*Slice of white bread: 40 litres

*Burger: 2,400 litres

*Kilogram of cheddar: 5,000 litres

*Cotton shirt: 2,700 litres

*Pint of beer: 160 litres

*125ml glass of wine: 120 litres

*Pint of milk: 1,760 litres