Hoekstra & Chapagain 2007 Water footprints of nations: water use by people as a function of their consumption pattern. Water Resources Management 21,

Water Footprint Concept

The water footprint is an indicator of water use related to the consumption of people.
The water footprint of a country is the volume of water needed to produce the goods and services consumed by its inhabitants.
It consists of two parts:
- Internal water footprint: water used from domestic water resources.
- External water footprint: water used in other countries to produce goods and services imported and consumed.
The study calculates the water footprint for each nation for the period 1997–2001.
- USA: average water footprint of $2480 m^3/cap/yr$
- China: average water footprint of $700 m^3/cap/yr$
- Global average: $1240 m^3/cap/yr$
Four major direct factors determining a country's water footprint:
- Volume of consumption (related to gross national income).
- Consumption pattern (e.g., high versus low meat consumption).
- Climate (growth conditions).
- Agricultural practice (water use efficiency).

Introduction

Traditional databases show water withdrawals in the domestic, agricultural, and industrial sectors.
Assessing water demand in a country typically involves adding water withdrawals for different sectors.
This approach doesn't reveal the water actually needed by people in relation to their consumption pattern.
Many goods consumed in a country are produced in other countries, affecting the real water demand of a population.
National water withdrawals may be substantial, but a large amount of the products are being exported for consumption elsewhere.
The water footprint concept was introduced in 2002 as a consumption-based indicator of water use, complementing traditional production-sector-based indicators (Hoekstra and Hung, 2002).
The water footprint of a nation is the total volume of freshwater used to produce the goods and services consumed by the people of that nation.
The water footprint includes use of domestic water resources and use of water outside the borders of the country.
Developed in analogy to the ecological footprint concept.
- Ecological footprint: area of productive land and aquatic ecosystems required to produce resources and assimilate wastes.
- Water footprint: indicates the water required to sustain a population.

Virtual Water Concept

Closely linked to the water footprint concept.
Virtual water is the volume of water required to produce a commodity or service.
Introduced by Allan in the early 1990s.
Importing virtual water can be a partial solution to water scarcity problems.
Virtual water import releases pressure on scarce domestic water resources, acting as an alternative water source.
Imported virtual water is also called ‘exogenous water’ (Haddadin, 2003).
Assessing a nation's water footprint requires quantifying flows of virtual water entering and leaving the country.
Starting from domestic water resource use, subtract virtual water flows leaving the country and add flows entering the country.

Study Objective

Assess and analyze the water footprints of nations.
Builds on earlier studies quantifying virtual water flows related to international trade of crop products (Hoekstra and Hung, 2002, 2005) and livestock products (Chapagain and Hoekstra, 2003).
The present study refines earlier studies by making improvements and extensions using the period of 1997–2001.

Method

A nation’s water footprint has two components: internal and external water footprint.
Internal Water Footprint (IWFP): use of domestic water resources to produce goods and services consumed by inhabitants.

Equation for Internal Water Footprint (IWFP)

$IWFP = AWU + IWW + DWW − VWEdom$

AWU is the agricultural water use (evaporative water demand of crops).
IWW and DWW are the water withdrawals in the industrial and domestic sectors respectively.
VWEdom is the virtual water export to other countries related to the export of domestically produced products.
Agricultural water use includes both effective rainfall and irrigation water used effectively for crop production.
Irrigation losses are not included, assuming they largely return to the resource base and can be reused.
External Water Footprint (EWFP): annual volume of water resources used in other countries to produce goods and services consumed by the inhabitants.

Equation for External Water Footprint (EWFP)

$EWFP = VWI − VWEre−export$

VWI is the virtual water import into the country.
VWEre-export is the volume of virtual water exported to other countries as a result of re-export of imported products.
Both internal and external water footprints include the use of blue water (ground and surface water) and green water (moisture stored in soil strata).
The use of domestic water resources comprises water use in the agricultural, industrial, and domestic sectors.
Data for the latter two sectors are from AQUASTAT (FAO, 2003).
Significant fractions of domestic and industrial water withdrawals return to the water system but are generally polluted, so they have been included in the water footprint calculations.
The total volume of water use in the agricultural sector is calculated based on the total volume of crop produced and its corresponding virtual water content.
The methodology for calculating the virtual water content of crop and livestock products is described in Chapagain and Hoekstra (2004).
Virtual water content (m3/ton) of primary crops is calculated based on crop water requirements and yields.
Crop water requirements are calculated per crop and per country using the methodology developed by FAO (Allen et al., 1998).
Virtual water content of crop products is calculated based on product fractions and value fractions.
Virtual water content (m3/ton) of live animals is calculated based on the virtual water content of their feed and the volumes of drinking and service water consumed during their lifetime.
Virtual water content is calculated for eight major animal categories: beef cattle, dairy cows, swine, sheep, goats, fowls/poultry (meat purpose), laying hens, and horses.
The virtual water content of livestock products is again based on product fractions and value fractions.

Calculating Virtual Water Flows

$VWF[ne, ni, c] = CT [ne, ni, c] × VWC[ne, c]$

VWF denotes the virtual water flow ( $m^3yr^{-1}$ ) from exporting country ne to importing country ni as a result of trade in commodity c.
CT is the commodity trade (ton yr-1) from the exporting to the importing country.
VWC is the virtual water content ( $m^3 ton^{-1}$ ) of the commodity, defined as the volume of water required to produce the commodity in the exporting country.
The study takes into account the trade between 243 countries, using trade data from the Personal Computer Trade Analysis System of the International Trade Centre (ITC, 2004).
Calculations are carried out for 285 crop products and 123 livestock products.
The virtual water content of an industrial product can be calculated similarly to agricultural products.
Due to the diverse range of industrial products and difficulty in finding detailed standardised national statistics, an average virtual water content per dollar added value in the industrial sector ( $m^3/US$ ) is calculated.
This is the ratio of the industrial water withdrawal ( $m^3/yr$ ) in a country to the total added value of the industrial sector ( $US/yr$ ), which is a component of the Gross Domestic Product.

Water needs by product

The total volume of water used globally for crop production is $6390 Gm^3/yr$ at the field level.
Rice has the largest share in the total volume water used for global crop production, consuming about $1359 Gm^3/yr$ , which is about 21% of the total volume of water used for crop production at field level.
Wheat is the second largest water consumer (12%).
Rice consumes much more water per ton of production than wheat due to the higher evaporative demand for rice production.
The global average virtual water content of rice (paddy) is $2291 m^3/ton$ and for wheat $1334 m^3/ton$ .
The virtual water content of rice (broken) that a consumer buys in the shop is about $3420 m^3/ton$ which is larger than the virtual water content of paddy rice.
Livestock products generally have a higher virtual water content than crop products because a live animal consumes a lot of feed crops, drinking water and service water in its lifetime before it produces some output.
In an industrial farming system, beef cattle take an average of 3 years before being slaughtered to produce about 200 kg of boneless beef; consuming nearly 1300 kg of grains, 7200 kg of roughages, 24 cubic meters of water for drinking, and 7 cubic meters of water for servicing.
With every step of food processing, part of the material is lost, resulting in a higher virtual water content of the product.
The global average virtual water content of maize, wheat and rice (husked) are 900, 1300 and $3000 m^3/ton$ respectively, whereas the virtual water content of chicken meat, pork and beef are 3900, 4900 and $15500 m^3/ton$ respectively.
The virtual water content of products strongly varies from place to place, depending upon the climate, technology adopted for farming and corresponding yields.
One cup of coffee requires for instance 140 l of water in average, one hamburger 2400 l and one cotton T-shirt 2000 l.
The global average virtual water content of industrial products is 80 l per US$.
In the USA, industrial products take nearly 100 l per US$.
In Germany and the Netherlands, average virtual water content of industrial products is about 50 l per US$.
Industrial products from Japan, Australia and Canada take only 10–15 l per US$.
In world’s largest developing nations, China and India, the average virtual water content of industrial products is 20–25 l per US$.

Water footprints of nations

The global water footprint is $7450 Gm^3/yr$ , which is $1240 m^3/cap/yr$ in average
India is the country with the largest footprint in the world, with a total footprint of $987 Gm^3/yr$ . While India contributes 17% to the global population, the people in India contribute only 13% to the global water footprint
The people of the USA have the largest water footprint, with $2480 m^3/yr$ per capita, followed by the people in south European countries such as Greece, Italy and Spain ( $2300–2400 m^3/yr$ per capita).
High water footprints can also be found in Malaysia and Thailand.
The Chinese people have a relatively low water footprint with an average of $700 m^3/yr$ per capita.
The size of the global water footprint is largely determined by the consumption of food and other agricultural products.
The estimated contribution of agriculture to the total water use ( $6390 Gm^3/yr$ ) is even bigger than suggested by earlier statistics due to the inclusion of green water use (use of soil water).
If we include irrigation losses, which globally add up to about $1590 Gm^3/yr$ (Chapagain and Hoekstra, 2004), the total volume of water used in agriculture becomes $7980 Gm^3/yr$ .
About one third of this amount is blue water withdrawn for irrigation; the remaining two thirds is green water (soil water).

Factors Determining Water Footprint

The four major direct factors determining the water footprint of a country are:
- Volume of consumption (related to the gross national income).
- Consumption pattern (e.g. high versus low meat consumption).
- Climate (growth conditions).
- Agricultural practice (water use efficiency).
In rich countries, people generally consume more goods and services, which immediately translates into increased water footprints.
The composition of the consumption package is relevant too, because some goods in particular require a lot of water (bovine meat, rice).
In many poor countries it is a combination of unfavourable climatic conditions (high evaporative demand) and bad agricultural practice (resulting in low water productivity) that contributes to a high water footprint.
Underlying factors that contribute to bad agricultural practice and thus high water footprints are the lack of proper water pricing, the presence of subsidies, the use of water inefficient technology and lack of awareness of simple water saving measures among farmers.
The water footprint of the USA is high ( $2480 m^3/cap/yr$ ) partly because of large meat consumption per capita and high consumption of industrial products.
The water footprint of Iran is relatively high ( $1624 m^3/cap/yr$ ) partly because of low yields in crop production and partly because of high evapotranspiration.
In the USA the industrial component of the water footprint is $806 m^3/cap/yr$ whereas in Iran it is only $24 m^3/cap/yr$ .
The aggregated external water footprints of nations in the world constitute 16% of the total global water footprint.
The share of the external water footprint strongly varies from country to country.
Some African countries have hardly any external water footprint because they have little import.
Some European countries have external water footprints contributing 50–80% to the total water footprint.
The agricultural products that contribute most to the external water footprints of nations are: bovine meat, soybean, wheat, cocoa, rice, cotton and maize.
Eight countries contribute fifty percent to the total global water footprint: India, China, the USA, the Russian Federation, Indonesia, Nigeria, Brazil and Pakistan.
India (13%), China (12%) and the USA (9%) are the largest consumers of the global water resources.

Conclusion

The global water footprint is $7450 Gm^3/yr$ , which is in average $1240 m^3/cap/yr$ .
The USA has an average water footprint of $2480 m^3/cap/yr$ whereas China has an average water footprint of $700 m^3/cap/yr$ .

Direct Factors Explaining High Water Footprints

Total volume of consumption, which is generally related to gross national income of a country. This partially explains the high water footprints of for instance the USA, Italy and Switzerland.
Water-intensive consumption pattern - high consumption of meat significantly contributes to a high water footprint. This factor partially explains the high water footprints of countries such as the USA, Canada, France, Spain, Portugal, Italy and Greece. The average meat consumption in the United States is for instance 120 kg/yr, more than three times the world-average meat consumption. Next to meat consumption, high consumption of industrial goods significantly contributes to the total water footprints of rich countries.
Climate - high evaporative demand, the water requirement per unit of crop production is relatively large. This factor partially explains the high water footprints in countries such as Senegal, Mali, Sudan, Chad, Nigeria and Syria.
Water-inefficient agricultural practice - water productivity in terms of output per drop of water is relatively low. This factor partly explains the high water footprints of countries such as Thailand, Cambodia, Turkmenistan, Sudan, Mali and Nigeria. In Thailand for instance, rice yields averaged 2.5 ton/ha in the period 1997–2001, while the global average in the same period was 3.9 ton/ha.

Reducing Water Footprints

Break the link between economic growth and increased water use, for instance by adopting production techniques that require less water per unit of product. Water productivity in agriculture can be improved for instance by applying advanced techniques of rainwater harvesting and supplementary irrigation.
Shift to consumptions patterns that require less water, for instance by reducing meat consumption. However, it has been debated whether this is a feasible road to go, since the world-wide trend has been that meat consumption increases rather than decreases. Probably a broader and subtler approach will be needed, where consumption patterns are influenced by pricing, awareness raising, labelling of products or introduction of other incentives that make people change their consumption behaviour. Water costs are generally not well reflected in the price of products due to the subsidies in the water sector. Besides, the general public is – although often aware of energy requirements – hardly aware of the water requirements in producing their goods and services.
Shift production from areas with low water-productivity to areas with high water productivity, thus increasing global water use efficiency. For instance, Jordan has successfully externalised its water footprint by importing wheat and rice products from the USA, which has higher water productivity than Jordan.

The water footprint of a nation is an indicator of water use in relation to the consumption volume and pattern of the people. As an aggregated indicator it shows the total water requirement of a nation, a rough measure of the impact of human consumption on the natural water environment.
one has to look at what is blue versus green water use, because use of blue water often affects the environment more than green water use. Also it is relevant to consider the internal versus the external water footprint. Externalising the water footprint for instance means externalising the environmental impacts. Also one has to realise that some parts of the total water footprint concern use of water for which no alternative use is possible, while other parts relate to water that could have been used for other purposes with higher added value. There is a difference for instance between beef produced in extensively grazed grasslands of Botswana (use of green water without alternative use) and beef produced in an industrial livestock farm in the Netherlands (partially fed with imported irrigated feed crops).
Consumptive water use, i.e. the volumes of water from groundwater, surface water and soil water that evaporate. The effect of water pollution was accounted for to a limited extent by including the (polluted) return flows in the domestic and industrial sector. The calculated water footprints thus consists of two components: consumptive water use and wastewater production. The effect of pollution has been underestimated however in the current calculations of the national water footprints, because one cubic metre of wastewater should not count for one, because it generally pollutes much more cubic metres of water after disposal (various authors have suggested a factor of ten to fifty).
International water dependencies are substantial and are likely to increase with continued global trade liberalisation. Today, 16% of global water use is not for producing products for domestic consumption but for making products for export. Considering this substantial percentage and the upward trend, we suggest that future national and regional water policy studies should include an analysis of international or interregional virtual water flows.