Water Footprint

The water footprint of an economic activity measures the volume of freshwater appropriated by that activity, including water consumed and water needed to account for pollution. It can include both direct water use and indirect use across the supply chain, within a specified geographical and temporal boundary. It differs from simple water withdrawal because it distinguishes the source and purpose of water use.

Components of the footprint

The total water footprint combines three components, each representing a different form of freshwater appropriation.

• The green water footprint is rainwater stored in the soil and consumed, mainly through evapotranspiration by crops.
• The blue water footprint is surface water or groundwater consumed, including water evaporated, incorporated into a product or otherwise not returned to the same catchment in the same period.
• The grey water footprint is the volume of freshwater theoretically required to assimilate pollutants so that specified water-quality standards are met.

Scope and calculation

An activity's footprint is obtained by aggregating relevant process water footprints within the chosen system boundary. It may be expressed as water volume per unit of time or, for a product, per unit produced, such as cubic metres per tonne.

• A product footprint covers relevant stages of production and includes direct water use and indirect water embodied in inputs and processing.
• For crops, it reflects climatic conditions, crop water requirements, irrigation, yield and pollutant loads from inputs such as fertilisers.
• For crop-based products such as ethanol, assessment may include cultivation, processing and allocation of water use among multiple products.

Interpreting sustainability

A water footprint is a volumetric accounting indicator, not a complete measure of environmental damage. The same volume can have different consequences depending on local water scarcity, season and the condition of the river basin or aquifer.

• Blue water use should be compared with locally available water, while grey water requirements should be compared with local pollution-assimilation capacity.
• Separating green, blue and grey components reveals dependence on rainfall, irrigation and pollution rather than hiding them within one aggregate figure.