1. The concept of ‘virtual water’
Virtual water is the water ‘embodied’ in a product, not in real sense, but in virtual sense. It refers to the water needed for the production of the product.
Global trade in goods and services brings
along global trade in ‘virtual water’
The adjective ‘virtual’ refers to the fact that most of the water used to produce a product is not contained in the product. The real-water content of products is generally negligible if compared to the virtual-water content.
‘Virtual water’ has also been called ‘embedded’ or ‘embodied water’. One can compare the concept to ‘embodied energy’ or ‘embodied labour’.

2. ► The Water Footprint of a product is the volume of fresh water used to produce the product, summed over the various steps of the production chain.
The water footprint of a product (good or service) is the volume of fresh water used to produce the product, summed over the various steps of the production chain. ‘Water use’ is measured in terms of water volumes consumed (evaporated) and/or polluted.

3. ► The Water Footprint of a product is the same as its ‘virtual water content’, but includes a temporal and spatial dimension:
when and where was the water used.
The ‘water footprint’ of a product is the same as the ‘virtual water content’ of the product. The term ‘water footprint’, however, is broader, in the sense that the water-footprint concept gives a spatial and temporal dimension to the concept of ‘virtual water content’. In this way, the water footprint offers a link to impact assessment and policy formulation. A water footprint is more than a figure for the total water volume used; it refers specifically to the type of water use and where and when the water was used.

4. ► The Water Footprint consists of three components: BLUE wf + GREEN wf + GREY wf
The ‘water footprint’ includes three components: consumptive use of rainwater (green water), consumptive use of water withdrawn from groundwater or surface water (blue water) and pollution of water (grey water).
The blue water footprint is the volume of freshwater that evaporated from the global blue water resources (surface and ground water) to produce the goods and services consumed by the individual or community. 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 can be 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.

5. ► Assessing the Water Footprint of a product requires analysis of the full production chain.
Assessing the water footprint of a product requires analysis of the full production chain. This will be illustrated with an example for cotton.

6. Production chain cotton
A cotton shirt is made from cotton fabric, which is made from combed or carded cotton, which is derived from cotton lint, which comes from seed cotton, which is harvested from the cotton field. Indeed, before the final cotton textile reaches to the hands of a consumer it passes through a number of intermediate processes and products. First the seed cotton is processed into lint (we get only 350 kg of lint out of 1000 kg of seed cotton), then after carding, spinning and weaving we get grey fabric (1000 kg of lint produces only 900 kg of grey fabric), then it goes to the wet processing (bleaching and dying) and finishes as final printed cotton textile. It requires about 30 m3 per ton for bleaching, 140 m3 per ton for dying and 190 m3 per ton for printing. The average water footprint of printed cotton (for example a pair of jeans weighing 1 kilogram) is litres per kilogram.

7. 2500 litres of water for 1 cotton shirt
Water footprint: 2700 litres for 1 cotton shirt. In order to get 1 kg of final cotton textile, one requires 11,000 litres of water (as a global average). Thus, when we have a shirt with a weight of 250 gram, this shirt costs 2700 litres. Of this total water volume, 45% is irrigation water consumed (evaporated) by the cotton plant; 41% is rainwater evaporated from the cotton field during the growing period; and 14% is water required to dilute the wastewater flows that result from the use of fertilisers in the field and the use of chemicals in the textile industry. Globally, the annual cotton production evaporates 210 billion cubic meters of water and pollutes 50 billion cubic meters of water. This is 3.5 % of the global water use for crop production.

8. The water footprint of products
global averages
1 kg wheat
1 m3 water
1 kg rice
3 m3 water
1 kg milk
1 kg cheese
5 m3 water
1 kg pork
1 kg beef
15 m3 water
Livestock products typically require more water per kilogram (or per calorie) than crop products.
[Hoekstra & Chapagain, 2008]

9. 40 litres of water for 1 slice of bread
Water footprint: 1300 litres of water for 1 kg of wheat. Wheat consumes about 790 billion cubic meters of water annually, which constitutes 12 % of the global water use for crop production. International trade in wheat is responsible for 75 billion cubic meters of virtual water exports annually, which is about 6% of the total sum of international virtual water flows.
40 litres of water
for 1 slice of bread

10. 1500 litres of water per kg refined sugar
Water footprint: 1500 litres of water for 1 kg of cane sugar. Sugar can be produced from different crops, such as sugar cane or sugar beet. We consider here the case of sugar cane. It takes about 175 litres of water to produce 1 kg of sugar cane. About 11% of the sugar cane is sugar, so that 1 kg of sugar cane gives 0.11 kg of sugar. Hence, for 1 kg of refined sugar we did require about 1500 litres of water. Sugar cane consumes about 220 billion cubic meters of water annually, which is 3.4 % of the global water use for crop production.
Photo: sugar cane field in Egypt.
1500 litres of water
per kg refined sugar

11. 1 egg =
135 litres
water
Water footprint: 3900 litres for 1 kg of chicken meat. In an industrial chicken farming system, it takes 10 weeks on average before the chicken is slaughtered. It will produce 1.7 kg of chicken meat. A chicken consumes about 3.3 kg of grains (mainly soybean meal, wheat, corn, canola meal and mill screen) and 30 litres of water for drinking and servicing the farmhouse. This means that to produce one kilogram of chicken meat, we use about 2 kg of grains and 20 litres of drinking and servicing water. Producing 2 kg of feed of this composition takes about 3.9 m3 of water on average.

12. = 140 litres of water
It costs about litres of water to produce 1 kg of roasted coffee. For a standard cup of coffee we require 7 gram of roasted coffee, so that a cup of coffee costs 140 litres of water. Assuming that a standard cup of coffee is 125 ml, we thus need more than 1100 drops of water for producing one drop of coffee. Drinking tea instead of coffee would save a lot of water. For a standard cup of tea of 250 ml we require 30 litres of water.
The world population requires about 120 billion cubic metres of water per year in order to be able to drink coffee. This is equivalent to 1.5 times the annual Rhine runoff and constitutes 2 % of the global water use for crop production. International trade in coffee products is responsible for 80 billion cubic meters of virtual water exports, which is about 6% of the international virtual water flows in the world. Among all the crop and livestock products coffee stands at the top position in the list of global virtual water flows.

13. 2400 litres of water for 100 gram of chocolate
The water footprint of pure chocolate is 2400 litres for a 100-gram bar (as a world average!). Composition of dark chocolate: 40% cocoa paste (water footprint litres/kg); 20% cocoa butter (water footprint litres/kg); 40% sugar (water footprint 1526 litres/kg). We then can calculate: 40% % % 1526 = litres/kg = 2400 liters for one 100gr chocolate bar. The water footprint of milk powder is 4600 litres/kg, so that milk chocolate will have a bit larger water footprint (about 2500 litres for one 100gr chocolate bar) than dark chocolate when total cocoa content remains the same. Most crucial for the water footprint of chocolate is the cocoa paste and cocoa butter content.
2400 litres of water for
100 gram of chocolate

14. 10 litres of water for 1 sheet of A4-paper
Water footprint: 10 litres of water for one A4-sheet of paper. We assume here eighty-grams paper (80g/m2). Further we assume that the paper is produced from wood.
10 litres of water
for 1 sheet of A4-paper

15. ► The Water Footprint is spatially explicit
► The Water Footprint is spatially explicit. Examples for coffee and cotton.
The water footprint has a spatial dimension, so it can be mapped. A water footprint map shows the volumes of water used at various locations, for example the water used worldwide to make the products consumed by a given community.

16. Water footprint of Dutch coffee consumption
Import of water in virtual form into the Netherlands related to coffee imports. Period Source: Hoekstra and Chapagain (2008), map 12.
[Hoekstra & Chapagain, 2008]

17. Water footprint of EU’s cotton consumption
blue water + green water + gray water
The impact of consumption of cotton products by citizens in EU25 on the world’s water resources (million m3/yr). Period Source: Hoekstra and Chapagain (2008), map 15.
[Hoekstra & Chapagain, 2008]

18. ► The Water Footprint of a nation is the total amount of water that is used to produce the goods and services consumed by the inhabitants of the nation.
The water footprint is an indicator of water use that looks at both direct and indirect water use. The water footprint of a nation is defined as the total amount of water that is used to produce the goods and services consumed by the inhabitants of the nation.

19. ► National Water Footprint = national water use + virtual water import
– virtual water export
The national water footprint can be assessed in two ways. In the top-down approach, the water footprint of a nation is calculated as the total use of domestic water resources plus the gross virtual-water import minus the gross virtual-water export. The bottom-up approach is to consider the sum of all goods and services consumed multiplied with their respective product water footprint.

20. Water footprint per capita
Average water footprint per capita per country. Green-colored countries have a water footprint per capita equal to or smaller than the global average; red-colored countries are beyond the global average. Period Source: Hoekstra and Chapagain (2008), map 9.
[Hoekstra & Chapagain, 2008]

21. Water dependency of nations
Many countries have net import of water in virtual form and a significant external water footprint::
most of Europe
North Africa
Middle East
Japan
Mexico

22. Consumer perspective Reduction of the direct water footprint:
water saving toilet, shower-head, etc.
Reduction of the indirect water footprint:
substitution of a consumer product that has a large water footprint by a different type of product that has a smaller water footprint;
substitution of a consumer product that has a large water footprint by the same product that is derived from another source with smaller water footprint.
Ask product transparency from businesses and regulation from governments
Examples of the first sort of substitution are replacing rice consumption in the Netherlands by potatoes or replacing cane sugar by beet sugar. An example of the second sort of substitution is replacing cotton clothes that originate from semi-arid regions with irrigated cotton fields by cotton clothes produced in wetter areas with rain-fed cotton growing. Both sorts of action require that the consumer is provided with proper information about the water footprints of specific products. For the first sort of substitution some general knowledge about the water footprints of different types of products may be sufficient, but for the second sort of substitution individual items need to be labelled in the shop. Source: Hoekstra, A.Y. (2008) Water neutral: reducing and offsetting the impacts of water footprints, Value of Water Research Report Series No.28, UNESCO-IHE.