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Mekonnen and Hoekstra (2011) provide a summary of national water footprints of production and consumption for countries around the world. They provide a guideline for the determination of the representative water footprint of various commodities that may be both produced within a country as well as imported for consumption from elsewhere around the globe. An example that is provided determines the average water footprint for tomatoes consumed in Germany. Using the data presented in Table 1.6, determine what the water footprint for tomato consumption in Germany is assuming the total quantity imported is consumed, using a weighted average of each water footprint for tomatoes imported from other countries.

Solution. Using a weighted average of the water footprint and Germany’s import levels from the countries listed in Table 1.6 yields the following results using Equation 1.1 for the calculations.

(1.1)

where Tomato Consumption = annual T of tomatoes produced or imported and consumed from each country, i; Water Footprint = m³ water/T tomatoes produced from each country, i; and n = total number of countries, including itself, from which Germany imports tomatoes. Substituting values from Table 1.6 into Equation 1.1 yields:

Table 1.6 Water footprint and quantities of German tomato consumption as a function of place of origin.

Place of origin	Quantity imported or consumed, T/yr	Water footprint, m3/T
Germany	47,000	36
The Netherlands	252,000	10
Spain	244,000	83
Italy	72,000	109
France	52,000	110
Total	667,000