The Water Footprint of Food
28 Sep 10
By Arjen Y. Hoekstra, University of Twente, the Netherlands
One single component in the total water footprint of humanity stands out: the water footprint related to food. About 85% of humanity’s water footprint is related to the consumption of agricultural products; 10% relates to industrial products and only 5% to domestic water consumption. Within the category of agricultural products, one sub-category stands out: animal products. Products derived from animals generally have a much larger water footprint per kilogram or caloric value than crop products. This means that if people consider reducing their water footprint, they better critically look at their diet than at their water use in the kitchen, bathroom and garden. Wasting water never makes sense, so saving water at home when possible is certainly advisable, but when we would limit our actions to water reductions at home, many of the most severe water problems in the world would hardly be lessened. The water in the Murray-Darling basin in Australia is so scarce mostly because of water use for the production of various types of fruits, vegetables, cereals and cotton. The Ogallala Aquifer in the American Midwest is gradually being depleted because of water abstractions for the irrigation of crops like maize and wheat. Much of the grains cultivated in the world are not for human consumption but for animals. In the United States, for example, 68% of the grains consumed is used for animal feed. Animal products do not have a relatively large water footprint because of the water volumes required for drinking, but because of the water needed to grow the feed. From a water-saving point of view, it is obviously more efficient to eat the crops directly then indirectly by having them first processed into meat.
Consumers can reduce their direct water footprint – i.e. their home water use – by installing water-saving toilets, applying a water-saving showerhead, etc. For reducing their indirect water footprint – that is the water consumption behind the production of food and other consumer products – they have basically two options. One option is to substitute a consumer product that has a large water footprint by a different type of product that has a smaller water footprint. Eating less meat or becoming vegetarian is one example, but one can also think of drinking tea instead of coffee, or even better plain water. Not wearing cotton but synthetic fibre clothes also saves a lot of water. But this substitution approach has limitations, because many people do not easily shift from meat to vegetarian and people like their coffee and cotton. A second option is that people stick to the same consumption pattern but select the beef, coffee or cotton that has a relatively low water footprint or that has its footprint in an area that does not have high water scarcity. This requires, however, that consumers have proper information to make that choice. Since this sort of information is generally not available, this in turn asks for an effort from businesses to create product transparency and an effort from governments to install the necessary regulations. Currently we are far removed from a situation in which we have relevant information about the environmental impact of one piece of beef compared to another piece. The water footprint of beef, however, greatly varies across production systems and countries and strongly depends on feed composition. The same holds for other food items.
The water footprint concept is an analogue to the ecological and the carbon footprint, but indicates water use instead of land or fossil energy use. The water footprint of a product is the volume of freshwater used to produce the product, measured over the various steps of the production chain. Water use is measured in terms of water volumes consumed (evaporated) or polluted. The water footprint shows volumes of water use and pollution, but also the locations, which is relevant, because the impact of water use depends on local conditions. A water footprint generally breaks down into three components: the blue, green and grey water footprint. The blue water footprint is the volume of freshwater that is evaporated from the global blue water resources (surface and ground water). The green water footprint is the volume of water evaporated from the global green water resources (rainwater stored in the soil). The grey water footprint is the volume of polluted water, which is quantified as the volume of water that is required to dilute pollutants to such an extent that the quality of the ambient water remains above agreed water quality standards.
Table 1 shows the global average water footprint for a number of common food products. The numbers show that, as expected, animal products are more water-intensive than food crops. However, what the averages hide is that there is a very large variation of the water footprint for each of the products shown in the table. Knowing these differences is essential if one has already chosen to buy a certain product but not yet chosen which of the various options that still remain. One piece of beef is simply not equal to the other one, even though the taste and all other measurable characteristics are the same. The history may be different.
Water consumption in relation to diet
Since food consumption gives the most important contribution to the water footprints of people, dietary habits greatly influence the associated water footprint. In industrialised countries, the average calorie consumption is 3400 kcal per day; roughly 30% of that comes from animal products. When we assume that the average daily portion of animal products is a reasonable mix of beef, pork, poultry, fish, eggs and dairy products, we estimate that 1 kcal of animal product requires roughly 2.5 litres of water on average. Products from vegetable origin, on the other hand, require roughly 0.5 litre of water per kcal, this time assuming a reasonable mix of cereals, pulses, roots, fruit and vegetables. Under these circumstances, producing the food for one day costs 3600 litres of water (Table 2). For the vegetarian diet we assume that a smaller fraction is of animal origin, but not zero, because of the dairy products still consumed. It is obvious that consumers can reduce their water footprint through reducing the volume of their meat consumption. Alternatively, however, or in addition, consumers can reduce their water footprint by being more selective in the choice of which piece of meat they choose to buy. Chickens are less water-intensive than cows and beef from one production system cannot be compared in terms of associated water impacts to beef from another production system.
Globalization of water
Protecting freshwater resources can no longer be regarded as an issue for individual countries. Let us take Europe as an example. The water footprint of Europe – the total volume of water used for producing all commodities consumed by European citizens – has been significantly externalised to other parts of the world. Europe is a large importer of crops like sugar and cotton, two of the thirstiest crops. Europe also imports large volumes of feed, like soybean from Brazil. European consumption strongly relies on water resources available outside Europe. How is Europe going to secure its future water supply? China and India are still largely water self-sufficient, but with rising food demand and growing water scarcity within these two major developing countries, one will have to expect a larger demand for food imports and thus external water demand.
Although in many countries most of the food still originates from the country itself, substantial volumes of food and feed are internationally traded. As a result, all countries import and export water in virtual form, i.e. in the form of agricultural commodities. Worldwide, trade in food products results in international virtual water flows that add up to 1250 billion m3/yr, which is equivalent to more than two times the annual runoff of the Mississippi. Within Europe, France is the only country with a net export of virtual water. All other European countries have net virtual water import, i.e. they use some water for making export products but more water is used elsewhere to produce the commodities that are imported. Europe as a whole is a net importer of virtual water. Europe’s water security thus strongly depends on external water resources. Related to this, a substantial proportion of existing problems of water depletion and pollution in the world relates to export to Europe.
Product transparency in the food sector
In order to know what we eat we will need a form of product transparency that is currently completely lacking. It is reasonable that consumers have access to information about the history of a product. The question is: how water-intensive is a particular product that is for sale and to which extent does it relate to water depletion and/or pollution? Establishing a mechanism that makes sure that such information is available is not an easy task. It requires a form of accounting along production and supply chains that accumulates relevant information all the way to the end-point of a chain.
Governments that put interest in ‘sustainable consumption’ may translate this interest into their trade policy. Given the fact that about 50% of the Italian water footprint lies outside its own territory, the Italian government could strive towards more transparency about the water impacts of imported products. National governments can tune their trade and development cooperation policies towards their wish to promote consumption of and trade in sustainable products. They can also put regulations in place that urge businesses along the supply chain of food products to cooperate in creating product transparency.
Business can have a key role, particularly the large food processors and retailers. Since they form an intermediary between farmers and consumers, they are the ones that have to pass on key information about the products that they are trading. As big customers they can also put pressure on farmers to actually reduce their water footprint and require them to provide proper environmental accounts. In addition, businesses can cooperate in water labelling, certification and benchmarking schemes and produce annual water accounts that include a report of the supply-chain water footprints and associated impacts of their products.
You can find more information on this subject in 6 languages on the site www.waterfootprint.org
This article was published in the italian magazine Slow Food N°45, in a section dedicated to Water.
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