The water footprint is composed of three colours: green, blue and grey (Hoekstra et al. 2011). The green process water
footprint is the volume of green water (rainwater) consumed during the production process of a good. It is the total rainwater evapotranspiration plus the water incorporated in the product. The blue-water footprint refers to consumption of
blue-water resources (surface- and groundwater). The bluewaterfootprint of a process is defined as the sum of blue-water
evapotranspiration, blue water incorporated into a product and lost return flow (water not returning to the same catchment area or water that is not returned in the same time period). It should be noted that consumptive use of blue water is generally smaller than water withdrawal, because water withdrawals partly return to the catchment. The blue-water footprint is hence the ‘net water withdrawal’. The grey-water footprint of a product, or production phase of a good, is an indicator of the degree of freshwater pollution that can be associated with production. It is the volume of freshwater that is required to assimilate the load of pollutants based on existing ambient water quality standards (Hoekstra et al., 2011). The grey-water footprint is determined by dividing the pollutant load by the difference between the maximum acceptable concentration for that pollutant and its natural concentration in the receiving water body.