Comparing Apples and Oranges: Virtual Water Flow and John Lennon’s Beautiful Idea

apple_orange_wikiWe need about 125 litres of water to grow an apple, and about 80 litres for an orange. A glass of apple juice: 230 litres. A glass of orange juice: 200 litres. See? When done right, comparing apples and oranges can lead us down some interesting paths.

The amount of water required to grow fruits, or to produce a food item (such as pizza) (Pizza is food, right?), or to make a consumer product (such as a pair of jeans) is called embodied water. From our previous example of apples and oranges, the embodied water for an apple is 125 litres (that’s about 500 – 600 glasses of water, depending on your glass). In case you are wondering, the embodied water of a margherita pizza is 1260 litres of water (that’s more than 5000 glassfuls). (That number – 1260 litres – is the global average embodied water for a 725 gramme margherita pizza, and changes depending on where you bake or eat it).

The water footprint of a product or a process can be further broken down in to three categories: Green, Blue and Grey water footprints.


Embodied water in products: Let’s look at the water footprints of some of the everyday items we would find in our refrigerators, pantries and closets.


 Water footprints of some things you might have at home. Top to bottom: pizza, beer, a pair of jeans, tea, coffee, chocolate, lettuce, milk. (The data comes from this resource maintained by the Water Footprint Network.

These numbers are not meant to start soul-stirring environmental slogans* such as “Save Water: Say No to Chocolate!”, “This Earth Day, Give Up Pizza!”, “Go Green: No Coffee!” (you can have coffeemug’s coffee-mug when you pry it from his cold dead hands), “Save our planet: Don’t Wear Pants!” (hold on, let’s think this through…). Knee-jerk reactions and hasty decisions based on a single metric (such as water footprint) will not solve our environmental problems. Before we decide to stay under-caffeinated or go pant-less, let us remember that chocolate, coffee or pants are not the worst offenders when it comes to water footprint. Still, these water footprint data should make us pause and think. We are consuming water not only when drinking or showering, but also when shopping at the grocery store or buying clothes on sale. How do international trade policies for these commodities affect the sustainability of global water reserves?

Virtual water: The embodied water in a product is also called virtual water. When countries import or export goods, a global virtualJAAlaan_withname water flow is set in motion. The concept of virtual water was introduced Dr. John Anthony Allan. He received the 2008 Stockholm Water Prize for his pioneering work, which showed how water, food, energy, economics and politics are interconnected. His work influenced how we think about sustainability today.

In his own words: “Should an individual run out of water, it would be much easier to access one tonne of grain than the 1000 tonnes of water required to produce it… International trade moves the “virtual water” from comparatively advantaged regions, where there is a surplus of soil water in soil profiles, to comparatively disadvantaged regions such as the [Middle East/North Africa] MENA region, where water is scarce. The U.S. Department of Agriculture and European Community export to MENA region as much water as flows down the Nile into Egypt for agriculture each year.” (Source: 1)

Virtual water flow in international trade – An example: We must think of these global virtual water flows as one big system. Isolating the imports and exports of individual countries might give a warped image of the overall sustainability of these flows. Let us look at the virtual water flows involved in Egypt’s wheat imports and Thailand rice exports. Through its wheat imports, Egypt saves about 3575 Mmof its national water resources per year. However, these imports result in a net global water loss of about 400 Mm3 per year.


 Virtual water flow of Egypt’s wheat import. (Source 2

We see the opposite in Thailand’s rice export. Thailand experiences a net loss of water due to rice exports, but those exports result in a net saving in the global water reserves. How? Let’s take Thailand’s rice export to Nigeria for example. Thailand loses about 1750 Mmof water by exporting rice to Nigeria. This loss (~1700 Mm3 per year), however, is less than Nigeria’s national water savings due to this rice import: about 3260 Mm3. (See the figure below. In this transaction, Nigeria saves water because rice yield in Thailand is higher than that in Nigeria.) So, we see an overall saving of global water reserves. And remember, a country’s loss in water due to one export may be compensated by the gains due to other imports.



 Virtual water flow of Thailand’s rice export. (Source 2

Water-rich regions of the planet can help in mitigating the challenges in the water-stressed regions through this virtual water ‘trade’. Maybe John Lennon had it right. But the economics and politics of one region depending on another… ugh, sustainability is wicked (3, 4, 5) messy and clumsy indeed (6).


John Lennon’s Imagine. “And the world will live as one.” Amen.

Take-home messages:

1. All food items and consumer products have some embodied water associated with them.

2. The embodied water is also called virtual water.

3. International trade of agricultural and industrial products determines the net import/export of virtual water.

4. We may feel good about ourselves by turning off running faucets or switching off the lights, but these measures may not wash away our environmental sins of wasting food or consumer products.

5. John Lennon was onto something.

Until next time. Meanwhile, don’t waste food. Don’t let the lettuce get soggy** or the milk go bad in the fridge. For now, you don’t have to give up pizza (or beer) and you definitely shouldn’t give up wearing pants. Please – and I can’t stress this enough – do wear pants.


*You want a slogan?



**I am referring to an actual report with the delightful name The Soggy Lettuce Report. Yes, it exists. Source: Prudential (2004), Soggy Lettuce Report 2004: Are We A Nation of Wasters?

Image courtesy:

Photo of Dr. J. A. Allan:

Others: Wikipedia


1. Allan, J. Anthony. Virtual water: A strategic resource global solutions to regional deficits. Groundwater 36.4 (1998): 545-546.

2. Chapagain, A.K. and Hoekstra, A.Y. and Savenije, H.H.G. (2006) Water saving through international trade of agricultural products. Hydrology and Earth System Sciences, 10 (3). pp. 455-468. ISSN 1027-5606

3. Seager, Thomas, Evan Selinger, and Arnim Wiek. Sustainable engineering science for resolving wicked problems. Journal of agricultural and environmental ethics 25.4 (2012): 467-484.

4. Brown, Valerie A., John Alfred Harris, and Jacqueline Y. Russell, eds. Tackling wicked problems through the transdisciplinary imagination. Earthscan, 2010.

5. Lach, Denise, Steve Rayner, and Helen Ingram. Taming the waters: strategies to domesticate the wicked problems of water resource management. International Journal of Water 3.1 (2005): 1-17.

6. Frame, Bob. ‘Wicked’,messy’, and ‘clumsy’: long-term frameworks for sustainability. Environ. Planning C 26 (2008): 1113-1128.


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