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Humanity’s Growing Impact on the World’s Freshwater

Dry river bed in Adelaide, South Australia. photo by Michael Coghlan, flickr/creative commons.

 

As the human population has climbed past seven billion, and the consumption per person of everything from burgers to blue jeans has risen inexorably, the finiteness of Earth’s freshwater is becoming ever more apparent.

It takes water to make everything, and the explosion of demand for all manner of products is draining rivers, shrinking lakes, and depleting aquifers.

Consider this: on average it takes 2,700 liters (713 gallons) to make a cotton shirt and 9,800 liters (2600 gallons) to make a pair of blue jeans.  The cotton crops growing in farmers’ fields consume most of that water; a smaller share is used in the factories that churn out the clothes.

On any given day we’re likely wearing more than 15,000 liters (~4,000 gallons) worth of water.  And if we slip on a pair of leather loafers, well, add another 8,000 liters (~2,100 gallons).  It takes a lot of water to grow the grain to feed the cow whose skin is turned into shoes.

Such figures might not matter if there was abundant water whenever and wherever we needed it – or if water had a substitute.  But water is limited, and there’s no substitute for it.  We need water to quench our thirst, to grow our food, to cool electric power plants, and to make cars, computers and all those cotton shirts.

And that’s why the size of humanity’s water footprint – and of yours and mine – matters.

In a study published this week in the Proceedings of the National Academy of Sciences, researchers Arjen Hoekstra and Mesfin Mekonnen of the University of Twente in the Netherlands, have made the most detailed estimate to date of the scale and patterns of humanity’s water consumption.

This is a tricky and complicated task.  Using a high level of spatial resolution, the researchers tabulated all the water from both rainfall and irrigation that’s consumed in making goods and services for the global population. To complete the picture, they added in the volume of water needed to assimilate the pollution generated along the way.  They calculated the annual average global footprint for 1996-2005, the most recent ten-year period for which the necessary data were available.

The result is a large number – 9,087 billion cubic meters (2,400 trillion gallons) per year.   That’s a volume equivalent to the annual flow of five hundred Colorado Rivers.

Agriculture accounts for a whopping 92 percent of that global water footprint.  Not only are crops naturally thirsty, we’re feeding more than a third of the global grain harvest to livestock to satisfy our desires for meat and other animal products. Added up, the average beef burger takes 2,400 liters (634 gallons) of water to make.

In fact diets heavy in meat largely explain why the average water footprint for the United States is twice the global average.  U. S. consumers eat 4.5 times more meat than the global average.

One of the most interesting findings of Hoekstra and Mekonnen is that one-fifth of humanity’s water footprint travels across national borders in the form of “virtual water” – the water embedded in products that are traded between countries. For Egypt, Israel, Iran, Jordan, Saudi Arabia and other water-scarce nations, the ability to externalize their water consumption by importing wheat and other thirsty grains allows them to save their scarce water for industrial production and other higher-value uses.

Photo: Virtual water report
Virtual water trade over the period 1996-2005. Only the biggest flows are shown. Source: Hoekstra and Mekonnen, PNAS early edition, 2012.

 

Yet some water-stressed countries export a great deal of virtual water to other countries. For example, according to U.S. Department of Agriculture statistics, the Central Asian nations of the Aral Sea basin export 96 percent of the cotton they produce. Large-scale cotton production in this region over the last half century has caused the Aral Sea, once the world’s fourth largest lake, to lose 80 percent of its water.  Much of the lake bed is now a salty wasteland.

The United States, blessed with a vast area of highly productive rain-fed cropland, is the world’s biggest exporter of virtual water, sending millions of tons of grain to countries around the world.  Its biggest virtual water imports come from China’s Yangtze basin, which produces a wide variety of goods for the U.S. market.

So what is a growing population to do to live within water’s limits and keep rivers flowing?

The short answer: consumers can alter their diets and buying habits to shrink their water footprints, and producers can use water more efficiently in making their products.

As corporations grow concerned about the risks water scarcity poses to their bottom lines, many are taking a careful look at their supply chains with an eye toward conserving water. Unilever, for instance, has helped Tanzanian tea farmers shift to drip irrigation so its Lipton tea bags have a lower water footprint. Patagonia, retailer of outdoor apparel, has gone a step further. Its eye-opening “Don’t Buy this Jacket” advertisement and its Common Threads Initiative to motivate companies and consumers to reduce, repair, reuse, recycle and re-imagine our world are helping to motivate water stewardship.

There are dozens more examples of organizations offering practical ways to shrink the size of our water footprints – from Meatless Mondays to the Alliance for Water Efficiency.

The movement to live prosperously while reducing our impact on the planet’s precious waters is beginning.  The pace at which it unfolds is up to us.

 

Sandra Postel is director of the Global Water Policy Project and lead water expert for National Geographic’s Freshwater Initiative.  She is the author of several acclaimed books, including the award-winning Last Oasis, a Pew Scholar in Conservation and the Environment, and one of the “Scientific American 50.”

To learn more:

Calculate your own water footprint.

Learn about the water footprint of U.S. consumption.

See how much water it takes to make everyday products.

Visit the Water Footprint Network.

 


Comments

  1. [...] out this National Geographic article, written by Worldwatch senior fellow and  Freshwater Fellow of the National Geographic Society, [...]

  2. [...] to understand issues like water use and scarcity when making consumer decisions.Check out this National Geographic article, written by Worldwatch senior fellow and  Freshwater Fellow of the National Geographic Society, [...]

  3. Katie
    Michigan
    March 19, 2012, 2:53 pm

    According to the Millennium Ecosystem Assesment annual global withdrawal of freshwater is estimated to rise 10% every decade. The consumptive use of water is used upward of 70% for irrigation and agriculture alone. This amount is staggering and really shows how important sustainable water research is. Whilst the population grows ands more and more developed nation have a higher demand for animal products the water supply dwindles.

    Agriculture and irrigation is a consumptive use of water,this means that the water will not return to the water cycle for human use. So therefore as the need for more agriculture increases the water supply will decrease. N

    Growing up you are taught to conserve water by turning it off while brushing your teeth or washing your hands, however is that really going to help solve our freshwater problems? The water that we really need to worry about is on as much larger scale as the author shows, it’s within the infrastructure of agriculture, economics, and population growth that is really affecting how much water wer have left.

  4. Radical Kray Z
    Singapore
    March 12, 2012, 6:10 am

    altering diets is not gonna help much. the occasional meat is mandatory for a healthy body. however , what we can do is cut down on UNnecessary things like exorbitant clothes or golf resorts.
    Food is necessary. Golf Resorts are not.

  5. Mariel Siscar
    Manila, Philippines
    March 1, 2012, 2:39 am

    @David Zetland: I’ve read about what happened to the Aral Sea and I’m deeply saddened by what I’ve read.

    We should really start with the children; teach them now about being aware of water (and carbon) footprints and set examples. Always explain why we have to be conscious of our actions. It could be tiresome to constantly remind them, but it woked for me and my siblings. My grandfather who raised us was very concerned that the world he knew as a child was no longer available for his grandkids to enjoy. We were raised to use as minimal water as possible, and still stay clean (re-use bath water to flush the toilet, limited water for bath, doing the all the laundry in 1 day to conserve water, instead of twice or thrice a week, etc.,). Now that I live on my own, I realize the practice we used to do helps in saving me money from water bills too. :D

  6. Seymour Lyphe
    February 22, 2012, 5:30 am

    @Jan: Go vegan and use up even more water in even more destructive totalitarian agriculture? Is that your plan? A dietary lifestyle choice will change NOTHING in the all destroying dominant culture! Have fun with your ideological purity, but please stand out of the way of those who FIGHT against the madness called Tar Sands and Industrial Civilization!

  7. Evan
    USA
    February 21, 2012, 2:40 pm

    So this article says that the answer to conserving water is to convince billions of people to change their lives to consume less water? While that would work, it’s a foolish notion. Government involvement, like providing incentive to farmers/corporations to use best management practices to conserve water, or the implementation and enforcement of environmental regulations would have a more definitive impact on water use. Politics, however, might be just as foolish a notion.

  8. Jan
    February 19, 2012, 2:06 pm

    Go vegan and conserve water. Once the water is gone, so is life.

  9. David Zetland
    February 18, 2012, 8:57 am

    I’d prefer to see policies in place that target local, sustainable use of water. No need to track footprints, change diet, etc.

    Will that happen in the Aral basin? Not unless rulers there decide they prefer sustainability over short term profits, i.e., don’t propose solutions that conflict with price signals.