The Water Footprint is an environmental parameter that indicates the quantity of fresh water used by a consumer, a community, a process or a production system.
The Water Footprint of a product, on the other hand, be it a good or a service, is defined as the total volume of fresh water used directly or indirectly for all stages of its production.
Like all environmental "footprints", the water footprint is a quantitative measure and as such is expressed in terms of total volume consumed in the unit of time (in liters or cubic meters/year).
The estimate of the WFP (Water Footprint) does not take place on the basis of the total water withdrawal since, being an indicator of "actual consumption", it cannot count the part of water withdrawn and not consumed and, at the same time, must necessarily take into account the evaporated water and polluted water used in production processes.
The calculation of the Water Footprint is therefore given by the sum of three elements that are distinguished on the basis of the use of water and its origin:
- Blue Water: Volume of fresh water withdrawn downstream from surface and groundwater that does not return (or returns at different times than expected) because it is used during a process. It generally concerns water destined for the domestic sphere, for the agricultural and industrial sectors;
- Green Water: Volume of rainwater that is withdrawn, absorbed and evaporated by plants and that which can seep into the soil or available in it as moisture. In this case, therefore, it mainly concerns the irrigation of the agricultural sector;
- Grey Water: Volume of polluted water calculated as the volume of water needed to dilute the pollutants released into a water body, restoring its quality standards. Gray water therefore concerns all the phenomena of contamination, for the most part of industrial origin, which can also involve any processes of eutrophication of the water.
In essence, the Water Footprint is a measure of the consumption and pollution of fresh water and offers a geo-localized view of how sustainable the water resource is in supporting human activity in a given geographical area.