A Global Assessment of the Water Footprint of Farm Animal Products
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- Mekonnen, M.M. & Hoekstra, A.Y. Ecosystems (2012) 15: 401. doi:10.1007/s10021-011-9517-8
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The increase in the consumption of animal products is likely to put further pressure on the world’s freshwater resources. This paper provides a comprehensive account of the water footprint of animal products, considering different production systems and feed composition per animal type and country. Nearly one-third of the total water footprint of agriculture in the world is related to the production of animal products. The water footprint of any animal product is larger than the water footprint of crop products with equivalent nutritional value. The average water footprint per calorie for beef is 20 times larger than for cereals and starchy roots. The water footprint per gram of protein for milk, eggs and chicken meat is 1.5 times larger than for pulses. The unfavorable feed conversion efficiency for animal products is largely responsible for the relatively large water footprint of animal products compared to the crop products. Animal products from industrial systems generally consume and pollute more ground- and surface-water resources than animal products from grazing or mixed systems. The rising global meat consumption and the intensification of animal production systems will put further pressure on the global freshwater resources in the coming decades. The study shows that from a freshwater perspective, animal products from grazing systems have a smaller blue and grey water footprint than products from industrial systems, and that it is more water-efficient to obtain calories, protein and fat through crop products than animal products.
Keywordsmeat consumption livestock production animal feed water consumption water pollution sustainable consumption
Global meat production has almost doubled in the period 1980–2004 (FAO 2005) and this upward trend will continue given the projected doubling of meat production in the period 2000–2050 (Steinfeld and others 2006). To meet the rising demand for animal products, the on-going shift from traditional extensive and mixed to industrial farming systems is likely to continue (Bouwman and others 2005; Naylor and others 2005; Galloway and others 2007). There is a rich literature on the expected environmental consequences of increased consumption of animal products (Naylor and others 2005; Myers and Kent 2003; McAlpine and others 2009; Pelletier and Tyedmers 2010; Sutton and others 2011), and on the pros and cons of industrial versus conventional farming systems (Lewis and others 1990; Capper and others 2009). Specific fields of interest include, amongst others, animal welfare (Fraser 2008; Thompson 2008), excessive use of antibiotics (Gustafson and Bowen 1997; Witte 1998; Smith and others 2002; McEwen 2006), the demand for scarce lands to produce the required feed (Naylor and others 2005; Keyzer and others 2005; Nepstad and others 2006) and the contribution of livestock to the emission of greenhouse gases (Pelletier and Tyedmers 2010; Tilman and others 2001; Bouwman and others 2011). Although it is known that animal products are very water-intensive (Pimentel and others 2004; Chapagain and Hoekstra 2003), little attention has been paid thus far to the total impact of the livestock sector on the global demand for freshwater resources. Most of the water use along the supply chain of animal products takes place in the growing of feed. As a result of the increasing global trade in feed crops and animal products and the growth of meat preservation over longer periods, consumers of animal products have often become spatially disconnected from the processes necessary to produce the products, so that the link between animal products and freshwater consumption is not well known (Naylor and others 2005; Hoekstra 2010; Hoekstra and Chapagain 2008).
There are earlier publications on the water use behind animal production (Steinfeld and others 2006; Galloway and others 2007; Pimentel and others 2004; Chapagain and Hoekstra 2003, 2004; De Fraiture and others 2007; Peden and others 2007; Van Breugel and others 2010; Renault and Wallender 2000), but a detailed comprehensive global assessment was lacking. The objective of the current paper is to provide such an assessment by quantifying the water footprint of farm animals and of the various derived animal products per country and per animal production system. The period of analysis was 1996–2005. The water footprint of a product consists of three colour-coded components: the green, blue and grey water footprint (Hoekstra and Chapagain 2008). The blue water footprint refers to the volume of surface and groundwater consumed (that is evaporated after withdrawal) as a result of the production of the product; the green water footprint refers to the rainwater consumed. The grey water footprint refers to the volume of freshwater that is required to assimilate the load of pollutants based on existing ambient water quality standards. Water footprint calculations have been based on the recently established global water footprint standard (Hoekstra and others 2011), which was developed based on earlier water footprint studies (see for example, Chapagain and others 2006; Hoekstra and Chapagain 2007; Gerbens-Leenes and others 2009; Aldaya and others 2010).
With the exception of Chapagain and Hoekstra (2003, 2004), no previous study has estimated the water footprint of animal products by product and country at a global level. Although Chapagain and Hoekstra (2003, 2004) were able to estimate the water footprint of farm animals and animal products per country, they have made very crude assumptions regarding the composition and amount of feed consumed by different animals. Besides, the water footprints of feed crops were estimated based on national average climatic data. The main differences with Chapagain and Hoekstra (2003, 2004) are: (1) we estimated the amount of feed consumed per animal category, per production system and per country based on estimates of feed conversion efficiencies and statistics on the annual production of animal products, (2) we took into consideration the relative occurrence of the three production systems (grazing, mixed and industrial) in each country and (3) we estimated the green, blue and grey water footprints of growing feed crops using a grid-based dynamic water balance model that takes into account local climate, soil conditions and data on irrigation at a high spatial resolution.
The Water Footprint of an Animal
We follow the water footprint definitions and methodology as set out in Hoekstra and others (2011). The blue water footprint refers to consumption of blue water resources (surface and groundwater) along the supply chain of a product. ‘Consumption’ refers to loss of water from the available ground-surface water body in a catchment area. Losses occur when water evaporates, returns to another catchment area or the sea or is incorporated into a product. The green water footprint refers to consumption of green water resources (rainwater in so far as it does not become runoff). The grey water footprint refers to pollution and is defined as the volume of freshwater that is required to assimilate the load of pollutants given natural background concentrations and existing ambient water quality standards.
We consider eight farm animal categories: beef and dairy cattle, pigs, sheep, goats, broiler and layer chickens, and horses. When estimating total feed amounts and total water footprints per category, we include ‘buffaloes’ in the category of ‘beef cattle’ and ‘asses and mules’ in the category of ‘horses’.
Feed[a,c,s,p] represents the annual amount of feed ingredient p consumed by animal category a in country c and production system s (ton/y), WFprod*[p] the water footprint of feed ingredient p (m3/ton), WFmixing[a,c,s] the volume of water consumed for mixing the feed for animal category a in country c and production system s (m3/y/animal) and Pop*[a,c,s] the number of slaughtered animals per year or the number of milk or egg producing animals in a year for animal category a in country c and production system s.
The Water Footprint of Feed Ingredients
Volume and Composition of Feed
The volume and composition of the feed consumed vary depending on the type of animal, the production system and the country. The amount of feed consumed is estimated following the approach of Hendy and others (1995), in which the total annual feed consumption (including both concentrates and roughages) is calculated based on annual production of animal products and feed conversion efficiencies. Only for horses we have used the approach as in Chapagain and Hoekstra (2003), which means that we multiplied the estimated feed consumption per animal by the number of animals, thus arriving at an estimate of the total feed consumed by horses.
Estimating Feed Conversion Efficiencies
Estimating the Total Annual Production of Animal Products
Estimating the Feed Composition
The composition of concentrate feeds varies across animal species and regions of the world. To our knowledge, there are no datasets with global coverage on the composition of feed for the different animals per country. Therefore, we have made a number of assumptions concerning the concentrate feed composition of the different animal species. According to Hendy and others (1995), the diets of pigs and poultry include, on average, 50–60% cereals, 10–20% oil meals and 15–25% ‘other concentrates’ (grain substitutes, milling by-products, non-conventional concentrates). Wheeler and others (1981) provide the feed composition in terms of major crop categories for the different animal categories. We have used these and other sources in combination with FAOSTAT country average concentrate feed values for the period 1996–2003 (FAO 2009) to estimate the diet composition of the different animal species. To estimate the feed in terms of specific crops per animal, we first estimated the feed in terms of major crop categories following Wheeler and others (1981). The feed in terms of major crop categories is further distributed to each crop proportional to the crop’s share in its crops category as obtained from FAO (2009). The roughage feed is divided into fodder, grass and crop residues using the data obtained from Bouwman and others (2005). The estimated fraction of concentrate feed in total feed dry matter, per animal category, production system and world region is presented in Appendix IV (Supplementary material).
A large amount of data has been collected from different sources. A major data source for animal stocks, numbers of animals slaughtered each year, annual production of animal products, and concentrate feed per country is FAOSTAT (FAO 2009). Other important sources that have been used are: Bouwman and others (2005), Seré and Steinfeld (1996), Wint and Robinson (2007), Hendy and others (1995), FAO (2003) and Wheeler and others (1981). Appendix V (Supplementary material) summarizes how specific data have been obtained from these different sources.
The Water Footprint of Animal Products per Ton
The Green, Blue and Grey Water Footprint of Selected Animal Products for Selected Countries and the Weighted Global Average (m3/ton)
Leather (beef cattle)
When we look at global averages (Table 1), we see that the water footprint of meat increases from chicken meat (4,300 m3/ton), goat meat (5,500 m3/ton), pig meat (6,000 m3/ton) and sheep meat (10,400 m3/ton) to beef (15,400 m3/ton). The differences can be partly explained from the different feed conversion efficiencies of the animals. Beef production, for example, requires 8 times more feed (in dry matter) per kilogram of meat compared to producing pig meat, and 11 times if compared to the case of chicken meat. This is not the only factor, however, that can explain the differences. Another important factor is the feed composition. Particularly the fraction of concentrate feed in the total feed is important, because concentrate feed generally has a larger water footprint than roughages. Chickens are efficient from a total feed conversion efficiency point of view, but have a large fraction of concentrates in their feed. This fraction is 73% for broiler chickens (global average), whereas it is only 5% for beef cattle.
For all farm animal products, except dairy products, the total water footprint per unit of product declines from the grazing to the mixed production system and then again to the industrial production system. The reason is that, when moving from grazing to industrial production systems, feed conversion efficiencies get better (Appendix I — Supplementary Material). Per unit of product, about three to four times more feed is required for grazing systems when compared to industrial systems. More feed implies that more water is needed to produce the feed. The fraction of concentrate feed in the total feed is larger for industrial systems if compared to mixed production systems and larger for mixed systems if compared to grazing systems (Appendix IV — Supplementary Material). The water footprint per kg of concentrate feed is generally larger than for roughages, so that this works to the disadvantage of the total water footprint of animals raised in industrial systems and to the advantage of the total water footprint of animals raised in grazing systems. This effect, however, does not fully compensate for the unfavorable feed conversion efficiencies in grazing systems.
In dairy farming, the total water footprint per unit of product is comparable in all three production systems. For dairy products, the water footprint happens to be the smallest when derived from a mixed system and a bit larger but comparable when obtained from a grazing or industrial system.
Blue and Grey Water Footprints per Ton of Product
All the above is about comparing the total water footprints of animal products. The picture changes when we focus on the blue and grey water footprint components. With the exception of chicken products, the global average blue and grey water footprints increase from grazing to industrial production systems (Table 1). The larger blue and grey water footprints for products obtained from industrial production systems are caused by the fact that concentrate feed takes a larger share in the total feed in industrial systems when compared to grazing systems. For beef cattle in grazing systems, the global average share of concentrate feed in total feed is 2%, whereas in industrial systems it is 21%. Mixed systems are generally somewhere in between. Although the feed crops that are contained in the concentrate feed are often to a great extent based on green water, there is a blue water footprint component as well, and the larger the consumption of feed crops compared to roughages, the larger the total amount of blue water consumed. This explains the larger blue water footprint per ton of product in industrial production systems for beef, milk, cheese, and pig, sheep and goat meat. The application and leaching of fertilizers and other agro-chemicals in feed crop production results in the fact that the grey water footprint of animal products from industrial systems, where the dependence on feed crops is the greatest, is larger than for grazing systems. Given the fact that freshwater problems generally relate to blue water scarcity and water pollution and to a lesser extent to competition over green water, industrial systems place greater pressure on ground- and surface-water resources than grazing systems, because grazing systems hardly depend on blue water.
In the case of chicken products (chicken meat and egg), the industrial production system has, on average, a smaller blue and grey water footprint per ton of product compared to the other two production systems. The reason is that chickens strongly rely on concentrate feed in all production systems, intensive or extensive. Broiler chickens in extensive systems have a share of concentrate feed in total feed of 63%, whereas this is 81% in intensive industrial systems. There is still a difference, but the differences in feed composition for both broiler and layer chickens is smaller if compared to the other animal categories. As a result, the relatively unfavorable feed conversion efficiency in extensive systems is not compensated by a more favorable composition of the feed as is in the other animal categories.
The trends in the global averages do not always hold for specific countries. This can be seen from Table 1, which provides country average water footprints for China, India, the Netherlands and the USA as well as global averages. The feed composition varies per production system but also from country to country; as a result, the magnitude of the different components of the water footprint in the different countries varies significantly from the global mean. Cattle in US grazing systems, for example, are also fed relatively large amounts of grains, predominantly maize, which is irrigated and fertilized, which explains the relatively large blue and grey water footprints of US beef from grazing systems. In China and India, cattle in grazing and mixed systems are mainly fed with pasture and crop residues that have no blue and grey water footprints. Beef from industrial systems in China and India, on the contrary, have a relatively large blue and grey water footprint, which can be explained from the fact that the concentrates in Chinese and Indian industrial systems have a relatively large blue and grey water footprint. This shows that systems that belong to the same category, grazing, mixed or industrial, differ in the feed they provide to animals. Often, the feed ingredients in the different countries have different water footprints, resulting in differences in the total green, blue and grey water footprint of the animal products.
The Total Water Footprint of Animal Production
During the period 1996–2005, the total water footprint for global animal production was 2,422 Gm3/y (87.2% green, 6.2% blue and 6.6% grey water). The largest water footprint for animal production comes from the feed they consume, which accounts for 98% of the total water footprint. Drinking water, service water and feed-mixing water further account the only for 1.1, 0.8 and 0.03% of the total water footprint, respectively. Grazing accounts for the largest share (38%), followed by maize (17%) and fodder crops (8%).
The global water footprint of feed production is 2,376 Gm3/y, of which 1,463 Gm3/y refers to crops and the remainder to grazing. The estimate of green plus blue water footprint of animal feed production is consistent with estimates of earlier studies (Table 4). The total water footprint of feed crops amounts to 20% of the water footprint of total crop production in the world, which is 7,404 Gm3/y (Mekonnen and Hoekstra 2011). The globally aggregated blue water footprint of feed crop production is 105 Gm3/y, which is 12% of the blue water footprint of total crop production in the world (Mekonnen and Hoekstra 2011). This means that an estimated 12% of the global consumption of groundwater and surface water for irrigation is for feed, not for food, fibers or other crop products. Globally, the total water footprint of animal production (2,422 Gm3/y) constitutes 29% of the water footprint of total agricultural production (8,363 Gm3/y). The latter was calculated as the sum of the global water footprint of crop production (7,404 Gm3/y, Mekonnen and Hoekstra 2011), the water footprint of grazing (913 Gm3/y, this study) and the direct water footprint of livestock (46 Gm3/y, this study).
Average Annual Water Footprint of One Animal, per Animal Category (1996–2005)
Water footprint of live animal at end of life time (m3/ton)
Average animal weight at end of life time (kg)
Average water footprint at end of life time (m3/animal)1
Average life time (y)
Average annual water footprint of one animal (m3/y/animal)2
Annual water footprint of animal category (Gm3/y)
% of total WF
Water Footprint of Animal versus Crop Products per Unit of Nutritional Value
The Water Footprint of Some Selected Food Products from Vegetable and Animal Origin
Water footprint per ton (m3/ton)
Water footprint per unit of nutritional value
Protein (liter/g protein)
Fat (liter/g fat)
Meat-based diets have a larger water footprint compared to a vegetarian diet. We explored the implications of our results by examining the diet within one developed country—the USA—to determine the effect of diet composition on water footprint. Meat contributes 37% towards the food-related water footprint of an average American citizen. Replacing all meat by an equivalent amount of crop products such as pulses and nuts will result in a 30% reduction of the food-related water footprint of the average American citizen.
The result of the current study can be compared with results from earlier studies. However, only a few other studies on the water footprint per unit of animal product and the total water footprint of animal production are available. We will first compare our estimates of the water footprints per ton of animal product with two earlier studies and subsequently we will compare the total water footprint related to animal feed production with five earlier studies.
The rough estimates made by Pimentel and others (2004) for the water footprints of beef and meat from sheep, pigs and chickens are partly very close to our global estimates but partly also quite different. As Pimentel’s studies did not include the grey water footprint component, we will compare only the green plus blue water footprint from our estimate with that of Pimentel and others (2004). They report a water footprint of chicken meat of 3,500 m3/ton, which is only a bit lower than our global average estimate of 3,858 m3/ton. They report a water footprint of pig meat of 6,000 m3/ton, which is a slightly larger than our global average estimate. For sheep meat, they report a water footprint of 51,000 m3/ton and for beef 43,000 m3/ton, values that are very high when compared to our estimates (10,400 m3/ton for sheep meat and 15,400 m3/ton for beef). We consider the values reported by Pimentel as rough estimates, for which the underlying assumptions have not been spelled out, so that it is difficult to explain differences with our estimates.
When we compare our estimates with Chapagain and Hoekstra (2004) at a country level, more differences are found (Figure 1B–F). The two studies show a relatively good agreement for pig meat, chicken meat and egg—although for egg the earlier study systematically gives higher numbers—but little agreement for beef and dairy products. In general we find that Chapagain and Hoekstra (2004) underestimated the water footprints for African countries and overestimated the water footprints for OECD countries. As already pointed out in the introductory section, there are three main reasons why the estimates from the current study can differ from the 2004-study and are considered more accurate. First, the current study is based on better data for the estimation of the quantity and composition of animal feed. Second, the current study takes into consideration the relative presence of the three production systems per country and accounts for the differences between those systems. Third, we have estimated the water footprints of the various feed ingredients more accurately by using a high-resolution grid-based crop water use model, including the effect of water deficits where they occur, making explicit distinction between the green and blue water footprint components and including the grey water footprint component.
Comparison of the Results of the Current Study with the Results from Previous Studies
Global water footprint1 related to animal feed production (Gm3/y)
Postel and others (1996)
Zimmer and Renault (2003)
De Fraiture and others (2007)
Rost and others (2008)
Hanasaki and others (2010)
There are several uncertainties in this study in the quantification of the water footprint of animals and animal products. Due to a lack of data, many assumptions have to be made. There are a number of uncertainties in the study, but particularly two types of uncertainty may have a major effect on the final output of the study. First, data on animal distribution per production system per country for OECD countries is not available. Wint and Robinson (2007) provide livestock distributions per production system per country for developing countries but not for OECD countries. For these countries we are forced to use the data from Seré and Steinfeld (1996), which provide livestock distribution per economic region. These data have the limitation that they are not country-specific and may lead to errors in distribution of animals into the different production system for some countries. The second major uncertainty is related to the precise composition of feed per animal category per country. Such data are not directly available so that we had to infer these data by combining different data sources and a number of assumptions. Despite the uncertainties in the data used, the order of magnitudes of the figures presented are unlikely to be affected. Similarly, the general findings regarding the overall comparison between different animals and different production systems and the comparison between animal versus crop products is not likely to change with better data.
Although the scope of this study is very comprehensive, there are many issues that have been left out. One issue is that we neglected the indirect water footprints of materials used in feed production and animal raising. We expect that this may add at most a few percent to the water footprint estimates found in this study (based on Hoekstra and others 2011). In the grey water footprint estimations we have looked at the water pollution by nitrogen-fertilizers only, excluding the potential pollution by other fertilizer components or by pesticides or other agro-chemicals. Besides, we have not quantified the grey water footprint coming from animal wastes, which is particularly relevant for industrial production systems. Neglecting nitrogen leaching and runoff from manure underestimates the grey water footprint related to animal production. The magnitude of this underestimate can roughly be shown by estimating the grey water footprint related to manure based on the global nitrogen input from manure found in the literature. Global nitrogen input from manure for the year 2000 varies from 17 million tons per year (Liu and others 2010) to 92 million tons per year (Bouwman and others 2011). Based on the relative contribution of manure to the total nitrogen input and the global total nitrogen leaching/runoff, the nitrogen leaching/runoff from manure can be estimated at 6.0–14.5 million tons per year. This amount of nitrogen leached/runoff to the freshwater systems can be translated into a grey water footprint of 600–1,450 Gm3/y. The grey water footprint is more significant in the intensive animal production system, which often generates an amount of waste that cannot be fully recycled on the nearby land. The large amount of waste generated in a concentrated place can seriously affect freshwater systems (FAO 2005; Steinfeld and others 2006; Galloway and others 2007). Finally, by focusing on freshwater appropriation, the study obviously excludes many other relevant issues in farm animal production, such as micro- and macro-cost of production, livelihood of smallholder farmers, animal welfare, public health and environmental issues other than freshwater.
In conclusion, we provide a detailed estimate of the water footprint of farm animals and animal products per production system and per country. The results show that the blue and grey water footprints of animal products are the largest for industrial systems (with an exception for chicken products). The water footprint of any animal product is larger than the water footprint of crop products with equivalent nutritional value. Finally, 29% of the total water footprint of the agricultural sector in the world is related to the production of animal products; one-third of the global water footprint of animal production is related to beef cattle.
The global meat production has almost doubled in the period 1980–2004 (FAO 2005) and this trend is likely to continue given the projected doubling of meat production in the period 2000–2050 (Steinfeld and others 2006). To meet this rising demand for animal products, the on-going shift from traditional extensive and mixed farming to industrial farming systems is likely to continue. Because of the larger dependence on concentrate feed in industrial systems, this intensification of animal production systems will result in increasing blue and grey water footprints per unit of animal product. The pressure on the global freshwater resources will thus increase both because of the increasing meat consumption and the increasing blue and grey water footprint per unit of meat consumed.
Managing the demand for animal products by promoting a dietary shift away from a meat-rich diet will be an inevitable component in the environmental policy of governments. In countries where the consumption of animal products is still quickly rising, one should critically look at how this growing demand can be moderated. On the production side, it would be wise to include freshwater implications in the development of animal farming policies, which means that particularly feed composition, feed water requirements and feed origin need to receive attention. Animal farming puts the lowest pressure on freshwater systems when dominantly based on crop residues, waste and roughages. Policies aimed to influence either the consumption or production side of farm animal products will generally entail various sorts of socio-economic and environmental tradeoffs (Herrero and others 2009; Pelletier and Tyedmers 2010). Therefore, policies aimed at reducing the negative impacts of animal production and consumption should be able to address these potential tradeoffs. Policies should not affect the required increase in food security in less developed countries neither the livelihood of the rural poor should be put in danger through intensification of animal farming.
This study provides a rich data source for further studies on the factors that determine how animal products put pressure on the global water resources. The reported incidents of groundwater depletion, rivers running dry and increasing levels of pollution form an indication of the growing water scarcity (Gleick 1993; Postel 2000; UNESCO 2009). As animal production and consumption play an important role in depleting and polluting the world’s scarce freshwater resources, information on the water footprint of animal products will help us understand how we can sustainably use the scarce freshwater resources.
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