Virtual water and free trade

Dalin et al argues in a recent article in the PNAS (Feb 2012):

. . . The water used throughout the production process of a good is referred to as virtual water.  

Importantly, China imports soy mostly from Brazil, the United States, and Argentina (Fig. 4A), and all these three countries produce soy with less water than China would use to grow this crop domestically (e.g., in 2007, the soy VWC was higher in China than in the three exporting countries) (Materials and Methods) (Table 1). Thus, imports of soybean to China contributed to saving water resources globally, and they were actually responsible for a substantial part (96%) of the global water savings associated with soy trade in 2007 and a significant part (36%) of the total global water savings in 2007 (Fig. 4B). 

This finding illustrates that food trade actually reduces global water use by transferring commodities to relatively less-efficient regions, because irrigation requirement per unit of crop varies widely among world regions (14, 15, 22). 

An interesting argument for free trade. See the Wikipedia entry on virtual water.