The Water Footprint (WF) of a crop product is defined as the volume of water use to produce it at the place of production. The WF accounts for the water use in the supply chain (indirect) and/or in the operations (direct). "Water use" is measured in term of water evaporated (i.e. water depleted from the system where it came from) and volume of water polluted through the use of pollutants (e.g. fertilizer).
The WF associated to the production of a product is the same as its Virtual Water Content (VWC), expressed in m3 of water use per ton of product produce. The VWC of unprocessed crops depends on the place and time of production and refers to the crop water requirement. It is expressed in term of water evapotranspiration because of the difficulty to separate transpiration of the crop from evaporation from the soil. The VWC consists of three components; the green, the blue and the gray component. The 'green' virtual water content of a crop refers to the total rainwater evapotranspiration from the field during the growing period. The 'blue' virtual water refers to the total volume of surface water or groundwater evapotranspiration during the growing period. The 'gray' virtual water content of a crop is the volume of polluted water generated during its production.
The Water Footprint Network (WFN) today is the central actor promoting the development of a water footprint methodology. On June 2009, SAI Platform issued a Discussion Paper with recommendations for the WFN. Click here to view the Discussion Paper.