File:Variation in blue water footprint for selected energy crops.jpg

English: Figure compares the water necessary to produce, transport, and convert a given crop into a fuel in two different regions. This shows important variations, and points to the need for careful matching of energy crops and production and conversion systems with available water supplies. The global trade in biofuel crops has created a ‘virtual water exchange’ where some countries with low water resources ‘export’ their water in the form of biofuels. It is important to consider not only the efficient use of water in the context of a single activity, but also the cumulative effects of several activities in one region on a watershed. Usually a distinction is made depending on the source of the water, for example whether production is entirely rainfed or irrigation is needed. An illustration of the water requirements of selected biofuel crops shows which biofuels demand the most water.