The term virtual water was first defined in 1998.
It is the volume of water required for making a product and the water used in the production chain.
Virtual water is comprised of 3 different components:
Different kinds of ‘coloured water’ (green, blue, grey and black-which is not virtual water) are classified based on where they are found in nature or the level of contamination of wastewater.
Green water is the soil moisture from precipitation, used by plants via transpiration.
It is part of the evapotranspiration flux in the hydrologic cycle.
Blue water is the freshwater: surface and groundwater.
It is stored in lakes, streams groundwater, glaciers and snow.
Grey water is polluted water which was not in contact with faecal matter .
Grey water is the product water of domestic activities: bathing, laundry and dishwashing or polluted water due to pesticides in agriculture and nutrients from fertilizers. agrilearner
It can be recycled and reused, not for drinking, but for irrigation. Since it was not in contact with human waste, it can be used for watering crops and other plants and is safely reabsorbed into the ground.
Grey water contains soap and fat particles, even hair. If the chemicals Agrilearner content is not too high, majority of plants are able to handle it. However, if grey water is to be used for irrigation it is highly advised that what goes down the drain is heavily regulated.