4. Water Footprint Assessment

Assessing the water footprint of any product, individual, city, country, etc. is a complex activity. The water footprint (WF) of a country depends on what products and how much of those products are consumed as well as the WF of each of those products, which changes depending on where it was produced. A complete understanding of a country’s water footprint requires measuring water used to produce goods then following the path of that water through virtual water trade to measure the water consumed within each country. Obviously, countries with large populations will have larger water footprints than countries with small populations, so it is more useful to analyze the water footprint on a per capita basis to compare water footprints between countries (Figure 2D.4.1).

Color coded map of all countries with countries in shades of red having above average water footprints per capita and countries in shades of green having below average water footprints per capita. Relevant information about specific countries or groups of countries is discussed in the paragraph text following this figure.
Figure 2D.4.1 Map showing the total water footprint of consumption per country in the period 1996–2005 (cubic meter per year per capita). Countries shown in green have a water footprint that is smaller than the global average; countries shown in shades of yellow to red have a water footprint larger than the global average. Source: Hoekstra and Mekonnen (2012). Found here. Used with permission.

The range of total WFs per capita is high for developing countries, ranging from 550–3,800 m3/y per capita. This range is narrower for industrialized countries, from 1,250–2,850 m3/y per capita. The United States is on the high end of this with a per capital WF of 2,842 m3/y while the United Kingdom is on the low end with a per capita WF of 1,258 m3/y. This is in large part due to food production choices. The U.S. consumes 4.5 times the amount of beef as the global average while the UK consumes only 2 times the global average of beef. This means the U.S. has a much higher green and blue water component in its WF put towards raising cattle, one of the higher virtual water content foods. In addition, how cattle are raised in the U.S. is very different than in the UK as the UK has a much smaller reliance on animal feedlots. The widespread usage of feedlots in the U.S. contributes to a higher grey water footprint related to cattle production.

Historically, governments have only assessed water used within the country (the internal water) to make national water plans. However, this fails to consider virtual water trade and the amount of water that was used in other countries and imported (the external water). In assessing the global water footprint for a country, both the internal and external water needs to be measured. Figure 2D.4.2 below shows the water footprint just for crops and animal products consumed by citizens of the United States. This set of maps shows the total water footprint per capita (bottom map), as well as how each of the three water footprint components (green, blue, and grey) contribute to this total (top three maps). On these maps, any water within U.S. borders is internal water and water in all other countries is external water that was imported to the U.S. via virtual water trade.

Series of 4 maps showing the global water footprint of U.S. citizens related to the consumption of crops and animal products from 1996 - 2005. Maps are green water footprint, blue water footprint, grey water footprint, and total water footprint. In all cases, the highest water usage is internal water (water within the U.S.), but these maps demonstrate that there is still water usage from all over the world that is part of the external water usage which is incorporated as virtual water in products imported to the U.S.
Figure 2D.4.2 The global water footprint of U.S. citizens related to the consumption of crops and animal products from 1996 – 2005. These maps demonstrate that crops and animal products do not only use internal water. Source: Hoekstra and Mekonnen (2012). Found here. Used with permission.

While most of the water footprint for U.S. citizens is internal water, roughly 20% is the result of external water. Most external water is green water used in agricultural production, which is logical as green water is the largest component of all national water footprints.

By using a comprehensive water footprint assessment, and categorizing both internal and external water, governments can make more informed water policy decisions that help reduce water stress and ultimately work towards a more globally sustainable use of water resources.

References

Hoekstra, A. Y., & Mekonnen, M. (2012). The water footprint of humanity. Proceedings of the National Academy of Sciences of the United States of America109(9), 3232-3237. https://doi.org/10.1073/pnas.1109936109

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