Sunday, May 15, 2011

Virtual water

The idea that freshwater is a finite resource which should not be wasted is gradually permeating our minds. At present, many people shudder at the mere thought of letting the tap drip without making good use of water or hearing that someone spends one hour having a shower, but this was not so in the past. In this sense, we are making good progress. However, how comes that our social awareness in water saving does not result in less water consumption? The answer is pretty simple: we are not aware of other water wasting processes. In other words, there are more ways to waste water other than a dripping tap.
If we take a look at water consumption figures worldwide, we will realise that household consumption is insignificant (less than 10%) and that most water is used in industries and agriculture. That is, our measures to save water at home are just the tip of the iceberg. Besides tap dripping water, there is the so-called virtual water, referred to the water used in the production of a good or service, which we actually don’t see. Everything manufactured or grown needs water to be produced and transported and it truly represents millions of cubic meters of wasted water. Let’s analyse some figures, but instead of cubic meters we will talk about “tap running minutes” in order to better understand its magnitude, taking into account that an average tap (without any water saving device available in the market, which are strongly recommended) pours 12 to 16 litres per minute. Therefore, our standard measurement is 14 litres of water running from an average tap every minute.
And now let’s face the figures:
To produce 100 grams of beef we need 10 cubic metres of water, equivalent to letting the tap run for 714 minutes (almost 12 hours!), whereas we only need 145 minutes of running water to produce 100 grams of rice, 178 minutes for 100 grams of milk and 47 minutes for 100 grams of potato.
The computer you are facing while reading this post requires a volume of water equivalent to 107 minutes of running water (1,500 litres).
The production of plastic products also requires huge amounts of water: 6 minutes of running water for each 1-litre bottle and 18 minutes for each 5-litre bottle.
Your jeans require 13 hours of running water and your cotton T-shirt almost 5 hours.
And for a car weighing one ton, the tap should be pouring water for almost three weeks.
Finally, we would need one year of running water to build a house.
Therefore, we can reach two conclusions: first, most water consumed is invisible to our eyes and secondly, this water does not come from our nearby rivers, sources or aquifers, but from the place of origin (production site or cultivation site) of this product. Hence, most rich countries are “importing” large volumes of water as products from Third World countries, many of them devastated or affected by droughts. We are not aware yet of our water footprint caused by consumption.


  1. Percentage of water consumption worldwide:
  2. Virtual water:
  3. Water saving devices:
  4. The data of water consumption in agriculture are taken from Worldwatch Institute report “State of the World 2004”:
  5. Water footprint:


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