Virtual Water

The Concept of Virtual Water and its Ambition

The term of Virtual Water refers to the fact that every good contains water, which has been used to produce the good. The adjective “virtual” means that the water is not necessarily contained in the final product. This measure of the amount of water, which has been used to produce the good, is carried out by adding the volume of freshwater consumed during the entire production chain (WATERFOOTPRINT 2010). This concept is sometimes also called the water footprint of a product, though with the same aims: Both concepts visualise the amount of “hidden” water that has been utilised for production. This is important to show because the production of goods is a global business today. As a result of global trade, the use of water has become spatially disconnected from the consumers (HOEKSTRA et al. 2009). At the same time, there are signs that the use of water exceeds a sustainable level in many parts of the world (MEKONEN & HOEKSTRA 2010). So, the concept of Virtual Water helps us to understand the global character of fresh water use which includes quantifying the effects of consumption and trade with water resources (HOEKSTRA et al. 2009).

The Three Colours of Virtual Water

(Adapted from HOEKSTRA 2009)

Water used during the production of any good can be divided into three different types of water, depending on the source of water and the type of pollution caused. Blue water means the amount of surface water (like lakes and rivers) and groundwater consumed. This blue water is used for irrigation and is lost through evaporation/runoff or because of incorporating into a product. The second part is called green water, i.e. , rainwater, the main source of water for rain-fed agriculture. Some of the rain water is being stored in the soil and can be used by plants. Both, green and blue water can vary of course within a year and from year to year as well. Finally, the grey water involves the water which has been polluted during he production (see also water pollution). It is defined as the volume of freshwater that is required to assimilate the load of pollution.

Examples of Products

Even if the concept is simple and well understandable, it is not easy to calculate the whole amount of water which has been used for a product. This is mainly because of the fact that every product has its own producing history. Nevertheless, most of the calculations are based on two different approaches. The first one is called chain-summation approach and is calculated, as the name suggests, by taking account all process steps during the whole production of a product. However, this approach can only be applied if a production system produces only one output product.

In a case where many products are necessary to produce an output product, the amount of water used is calculated by summing the water use of the input products and by adding the water consumed during each processing step. This is called the step-wise approach (HOEKSTRA et al. 2009).

In general, livestock products generate a much higher virtual water content than crop products. As an example, a cow needs approximately 3 years until it can be slaughtered for 200 kg of beef. During this time, a cow consumes nearly 1300 kg of grain, 7200 kg of roughage and 31’000 kg of water for drinking and servicing. Of course, the production of feed also requires water, so that with every step of food processing, part of material is lost because of selection and inefficiencies. The higher a product is positioned in a product chain, the higher will be the virtual water content of the product (CHAPAGAIN & HOEKSTRA 2004).

The units which express the virtual water content are in terms of cubic metres of water per ton of the product (=litres/kg). Below there are some virtual water contents of chosen products.

Virtual Water Trade and Globalisation

Goods are today being exported and imported all over the world. This implies that the virtual water content is also traded with the goods. So, the virtual water concept can be used to highlight the pressure on the available domestic water resources. The import of virtual water can be seen as an alternative water source (CHAPAGAIN & HOEKSTRA 2004). Furthermore it can be applied as an instrument to achieve water security as well as efficient water use. From an economic perspective, it makes sense to produce the water-intensive products in those places where water is most abundantly available. Virtual water trade from a nation where water is more than abundant to a nation where water is often scarce can effectively help to save water as seen from a global perspective (HOEKSTRA 2003). In order to show how a country performs in terms of water trade, it is helpful to quantify the flows of virtual water leaving and entering the country (CHAPAGAIN & HOEKSTRA 2004). If the resulting number is negative, the respective country imports more virtual water than it exports. This can be a sign of high water scarcity as one would expect. But there are countries which exhibit a low water scarcity and therefore should show a positive virtual water balance. However for different reasons, those countries (e.g. Indonesia) still have to rely heavily on virtual water import and therefore a net import of water can be noticed (HOEKSTRA 2003).

It is estimated, that the virtual water trade between nations lies in the range of approximately 1040 × 109m³/year of which 67 % relates to international trade of crops, 23 % to trade of livestock and 10% to trade of industrial products (HOEKSTRA 2003).

See concept to learn more about sustainable approaches to water and wastewater management.