Definition of Virtual WaterEach product contains a given amount of virtual water. It corresponds to the sum of the water incorporated during its elaboration during each step of the process.
Only water that does not come back to the same water catchment or that was altered (polluted) is taken into account.
Blue, green and grey waterVirtual water sources belongs to 3 categories.
Blue water is the most obvious one. It comes from lakes, rivers, underground sources.
Domestic and irrigation water are blue.
Water is considered as being used when it evaporates, is incorporated in products, goes to the sea or to another catchment and eventually when returning to the same catchment at a different period.
Green water is rain water plus the natural sol moisture.
It is generally more renewable than blue water.
Grey water corresponds to polluted water output of agriculture, industries and domestic usage.
Each liter of polluted water (grey water) will contaminate and certain amount of clean water making it unusable downstream.
In other words the grey water amount equals to the volume of clean water necessary to dilute pollution in order to comes back to natural concentration.
Margherita Pizza example
Pizza margerita is made of tomato puree, wheat flour and mozarella.
Water is needed to grow tomatoes, wheat and food for the cows. It comes from irrigation (blue water) and/or from rain and soil moisture (green water).
Fertilizers and other chemicals used in agriculture are released in rivers.
The virtual water content of a 725g pizza is about 1200 litres in Italy:
- 73% coming from mozzarella production, especially during the growth of the cow feed
- 24% from flour
- 3% from tomatoes
It is the sum of blue, green and grey water used thorough the production of these 3 ingredients.
Definition of water footprintThis is a more larger concept.
We can talk about the water footprint of a consumer (the sum of virtual water contained in the products he/she buys), a business (via the products it manufactures), a nation (taking into account footprint of local product, imports and exports) , etc...
It is focused not only on the water content of products but also to various factors such as the country of production, origin of the water, time of use, geopolitics, economical consideration, etc...
Geographic differencesThe footprint of a product varies from country to country.
This is especially true with agriculture with the climate directly acting on evapotranspiration.
Northern countries have also a far more larger water footprint - around 2 millions of liters per capita and per year - compared to countries under development and despite better climatic conditions.
Two main reason:
- they are eating more meat
- they are consuming much more industrial product
Murray River and Aral Sea examplesFinally, water is not really lost because it evaporates, goes into the ground or return polluted to river but withdrawing water for any use deprives temporally usage the same source of water for further use downstream.
Australia is relatively arid country with a few rivers.
Murray river used to be a large one in south Australia, having its mouth near Adelaide.
However, because of the climate and the number of farmers, upstream withdrawal due to irrigation has been so intense that the river ends up in a mud lake and does not reach Adelaide anymore in summer.
Citizens are supplied by bottle waters, what a paradox for a developed country !
Aerial view of the mouth of Murray River.
Applying water footprint concept would have certainly demonstrate that agriculture is not really sustainable in this region. A part of the products should be imported from areas with a most favorable climate; producing more meet with fewer water.
This way, a vital amount of water would remain available for domestic usage in Adelaide region.
The dying Aral Sea is yet another famous example.
The Russian Empires has started to develop the culture of cotton in Central Asia when it was no more possible to import it from America during the American Civil War.
The Soviet Union, so stubborn when it comes to production and ideology, has drastically improved the output, pumping all the water from the 2 rivers - Syr-Daria and Amur-Daria - feeding the Aral Sea.
The Aral Sea is reduced to a small lake in Uzbekistan nowadays.
Again cotton was not sustainable in these areas.
The population growing, the culture of rice and wheat has expanded as well, swallowing more blue water.
Economic considerations may cope with water preservation if agriculture ares move to region with more rain. Indeed, rain-fed culture uses mainly rain water present in the soil and reduce irrigation level.
One good example is the culture of wheat in Kazakhstan which is using solely green sources.
Water footprint of sample products in litres
|1kg of beef||15500|
|1kg of cheese||4900|
|1kg of chicken||3900|
|1 cotton Tshirt||2700|
|1 litre of milk||1000|
|1kg of apple||700|
|1kg of tomato||180|
|1 cup of coffee||140|
|1 year of washing machine||20000|
|What drinks a person per year||1000|
Trading products may lessen water footprintConsider a fictive example where 2 countries, A and B, are producing the same products, X and Y.
Country A has the most favorable water footprint on X and Y.
However, even a partial trade may cut down the overall footprint of both nations pertaining to both products.
If a part of X production, requiring more water is done by A for country B and, if B takes a part of the production of Y and sells it back to A, we ends up with a better water footprint.
This example just illustrates that some trade opportunities needs to be considered when it comes to global water preservation.
Use the right water at the right place !
Note that this may be somehow in opposition to carbon dioxide reduction due to the corresponding transport of virtual water.
Middle-East countries have well understand the advantages of trading virtual water although water is not officially a trade good.
As they are seriously lacking of water resources, they import most of their food - at a reasonable price - , keeping their tiny reserves for their domestic or industrial needs.
Virtual water of products on iPhone®Retrieve all the product with our iPhone application.
Water Aflamed, water footprint calculator