Virtual water

Virtual water is the volume of water used to make a product, and is the sum of the water use in the various steps of the production chain. Virtual water comprises three components of different colours: the green, blue and grey waters

1. Green water is the water transpired by the plant that comes from rain water stored in soil. Soil is a storage reservoir for the green water that falls from the sky, or that which has been added through irrigation from blue-water reservoirs.
2. Blue water is the water in our surface and groundwater reservoirs. In irrigated agriculture, blue water is abstracted to maintain transpiration. It is imperative that it is used with a high level of efficiency.
3. Grey water is the water that becomes polluted during production, say in agriculture because of the leaching of nutrients and pesticides. Grey-water volume can be quantified by calculating the blue water that would be required to dilute the receiving water body to an acceptable quality standard.