Products labelled with their carbon footprints are slowly making their way into the marketplace - for example, Timberland Co., a U.S. footwear maker, has identified the environmental impact of many of its shoe lines.
But imagine buying an apple with this label: It took 68 litres of water to produce this fruit.
Water footprints may soon be coming to a store near you.
As global leaders scramble to reach a deal on climate change this week in Copenhagen, environmentalists are hoping a topic that isn't on the agenda - water scarcity - will be the next big issue to capture the world's attention. For the consumer, that means pointing out just how much water is needed to produce items we use every day.
"I think personally that water footprints are much more tangible for people than the concept of a carbon footprint - it's amazing to see people's reactions when they see that 25,000 litres of water go into making a pair of shoes," says Karen Kun, co-founder of Waterlution, a Toronto-based non-profit organization for water education.
"People would respond very well to products being clearly labelled with their water footprint - consumers are crying out for mainstream products to have the right information so they can make their own choices."
The movement to label water footprints saw its first victory this year when Finnish food conglomerate Raisio launched the first voluntary example - 101 litres of water for each 100 grams of its oat flakes breakfast cereal.
And over the past few years, about 60 large companies have signed on to the United Nations' CEO Water Mandate, an informal pledge to lower their water footprints. They include Coca-Cola, Bayer, Cadbury, Dow Chemical, Heineken, Unilever and Siemens.
"All over the world, we consume products that don't include the cost of the water, and this needs to be changed," says Arjen Hoekstra, creator of the water footprint concept. Dr. Hoekstra is a professor at the University of Twente in the Netherlands and scientific director of the Water Footprint Network.
"This is why the concept of a water footprint is useful, to try and show the link between consumption and the creation of those products, and show the consumer's responsibility for the waste."
Some surprising statistics: A cup of coffee typically needs more than 140 litres of water to produce. For one kilogram of beef, it's about 15,150 litres.
Food usually accounts for about 70 per cent of each person's total footprint, but consumer products, such as jeans, cellphones and eyeshadow, require far more water per purchase. A cotton T-shirt soaks up 2,700 litres of water, a microchip needs 30 litres and a car requires more than 150,000 litres.
Of course, footprints can vary from product to product. Beef from cattle raised on soy will carry a different water footprint than meat from cattle fed on grain, and leather jackets made by different designers will vary from one another, which is why many environmentalists are calling for the development of a standardized label.
Dr. Hoekstra is wary of all the corporate interest in the water footprint: "They are all embracing the concept of the water footprint for the same reason they embraced the carbon footprint - because there is a lot of money to be made, not because they are serious about water conservation," he says. "There has been a great deal of hype made over carbon footprints, and you will see the same thing happen with the water footprint as it moves up the political agenda."
In fact, experts say climate change and water scarcity are inextricably linked: Higher temperatures and changing precipitation patterns - along with population growth, deforestation and diversion of water for dams, urbanization and industry - will mean that by 2025, more than two-thirds of the world's population will have to deal with chronic water shortages, according to the UN World Water Assessment Program.
According to the UN, one-third of the world's population currently suffers from water scarcity, when less than a decade ago it was thought the world would not reach that point until 2025.
Dr. Hoekstra says he hopes a labelling standard for the water footprint will avoid the mistakes made with carbon footprints, which use language that makes it easy "to confuse people and for vested interests to appear as though they are doing something substantial when it is the least effort they could make."
For instance, carbon offsets have been fraught with problems: Any individual, company or country can claim to be "carbon-neutral" by purchasing offsets rather than implementing carbon-reducing strategies first. And not all offsets are created equal. They vary widely in quality and impact - investment in renewable-energy projects in developing nations are considered superior to tree-planting schemes, for example.
"Already we are hearing people talk about water offsets - because it's cheaper to spend the money on some nice project somewhere than on reducing the operation's actual water footprint," Dr. Hoekstra says.
Even so, helpful and clear water-footprint labels won't tell the whole story. Listing the volume of water used to grow an orange doesn't tell a consumer anything about the agricultural or water systems in the place where it was grown. For example, would an apple grown in rainy British Columbia carry as high an ecological price as one in an irrigated grove in California that piped water in and depleted groundwater sources hundreds of kilometres away?
And water footprints combined with carbon footprints could become even more confusing for harried shoppers: Which is more important?
"You cannot convey all information in a label about water and its complexities in an easy way," Dr. Hoekstra concedes. So even the creator of the water footprint acknowledges that for consumers, it won't be easy being blue.
Zoe Cormier is a London-based writer specializing in science and the environment.