Posted 10 September 2007
National water footprints for selected countries (after Hoekstra & Chapagain, 2007)
A new study has quantified the cost of consumption of goods and services to our global water supplies. By comparing the consumption patterns of different countries, strategies can be developed to improve water use efficiency and reduce our impact on water resources.
Researchers from the University of Twente in the Netherlands have collaborated with the UNESCO-IHE Institute for Water Education to develop the water footprint concept as a measure of water consumption.
The water footprint of a population is the quantity of water required annually to sustain the consumption of goods and services by that population. The total amount of water consumed by all humans in a year is the global water footprint, which is contributed to by the national water footprint of each country, and ultimately by the water footprint of each individual.
The total global water footprint is 7450Gm3/yr*, which is an average of 1240m3/yr for every person on earth. This is about half the water required to fill an Olympic swimming pool.
Water footprints are calculated using the virtual water content of products and services. The virtual water content of a product is the volume of water required to produce it.
By far, the greatest single factor contributing to the global water footprint is crop production, responsible for about 85% of all water use. Rice production is the highest water consumer, accounting for about 21% of the total water used for crop production, while wheat production is the second highest consumer, at around 12%.
The virtual water content of products increases when additional resources are required for their production such as processing, packaging and transport. Processing of rice suitable for sale in shops requires 50% more water than that required to produce the raw ingredient.
This means that the total amount of water used by all of the resources and processes to generate products is reflected in the virtual water content of individual items. So for example, to produce a single 125ml cup of coffee requires the use of about 140 litres of water, and one cotton t-shirt requires around 2000 litres of water to produce.
Because production of meat requires so many additional resources than those needed to produce crops, it has a much higher virtual water content. The feed and water consumed by farmed cattle, combined with a relatively long production time, contribute to a virtual water content of about 15500 litres per kilogram of beef. This equates to about 2400 litres for a hamburger and 8000 litres for a pair of leather shoes.
Product | Virtual water content (litres) | |
1 glass of beer (250 ml) | 75 | |
1 glass of milk (200 ml) | 200 | |
1 cup of coffee (125 ml) | 140 | |
1 cup of tea (250 ml) | 35 | |
1 slice of bread (30g) | 40 | |
1 slice of bread (30g) with cheese (10 g) | 90 | |
1 potato (100 g) | 25 | |
1 apple (100 g) | 70 | |
1 cotton T-shirt (250 g) | 2000 | |
1 sheet of A4 paper (80 gsm) | 10 | |
1 glass of wine (125 ml) | 120 | |
1 glass of apple juice (200 ml) | 190 | |
1 glass of orange juice (200 ml) | 170 | |
1 bag of potato crisps (200 g) | 185 | |
1 egg (40 g) | 135 | |
1 hamburger (150 g) | 2400 | |
1 tomato (70 g) | 13 | |
1 orange (100 g) | 50 | |
1 pair of shoes (bovine leather) | 8000 | |
1 microchip (2 g) | 32 | |
Global average virtual water content of some selected products, per unit of product (from Hoekstra and Chapagain, 2007).
Quantification of the water cost of goods and services allows comparison of the consumption patterns of different populations on a country by country basis to identify factors contributing to national water footprints and how they might be reduced.
The study found that national water footprints vary due to four main factors.
The first is volume of consumption, which is directly related to the gross national income of a country. Because wealthier countries are higher consumers they have higher water footprints.
The second factor is the type of goods consumed by a population. Because production of some goods requires more water than others, their consumption can contribute to a higher footprint. Because meat requires a far greater volume of water to produce than other foods, countries with high meat consumption tend to have larger water footprints.
Climate is the third factor, because the availability of water due to climatic conditions has a direct impact on the amount of water available for use.
The fourth factor is efficiency of water use in agriculture. Low water productivity due to poor management of water resources for agriculture can contribute to a higher footprint.
India has the largest water footprint of any nation at 987Gm3/yr. However, on a per capita basis, the USA has the largest water footprint of 2480m/3/cap/yr. This is due in part to the high consumption of meat and industrial goods by this relatively wealthy nation. As a result, while USA has less than one third the population of India, each US citizen accounts for the consumption of nearly three times as much water as each citizen of India.
Australia has a water footprint of 1393m3/cap/yr, which is above the global average. Of the nations sampled, Australia has the highest rate of internal domestic water use per person of 341m3/cap/yr.
National water footprints have two components: the internal and external footprints. The internal water footprint is determined by the quantity of water used to produce goods and services that are consumed by the inhabitants of that nation. The external water footprint of a country is a measure of the volume of water used in other countries to produce goods and services for consumption by inhabitants of that country. Importing food and industrial goods contributes to the external water footprint because the water resources of other nations are used for their production.
The authors suggest a number of ways of reducing water footprints.
Developing more water efficient methods for the production of goods would reduce the footprint of countries with high consumption. This could be achieved by improvements to rainwater harvesting and irrigation technologies.
Another method would be to reduce consumption of products that require high volumes of water to produce, such as meat. However, because all populations exhibit similar patterns of increasing consumption with increasing wealth, this might be better achieved by changes to labelling, raising public awareness and raising prices to better reflect the water costs of production.
Finally, global water use efficiency can also be improved by shifting production from countries with low water productivity to those with high water productivity. This would mean increasing the external water footprint of counties with low domestic supply by the importation of goods from countries that have more water resources.
*One m3 is a cubic metre. A cubic metre contains 1,000 litres. One Gm3 or giga-cubic metre is one billion cubic metres. This contains one trillion (1,000,000,000,000 or 1×1012) litres.
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