The Water Footprint (WF) is a multidimensional indicator of appropriation (use, consumption and contamination) of fresh water resources, that contemplates 2 dimensions, direct and indirect, and three types: blue, green and grey. Direct use refers to the direct use of water by a consumer or producer, whereas indirect use refers to the volume of water in the whole production chain of a good or service (sometimes known as virtual water).
Evaluating the Water Footprint makes visible the way in which water is used by the environment, by city economies, by production practices in the agricultural and industrial sectors and by the daily habits of the population, and makes it possible to compare the true supply with the true demand, including water contamination, and thus promote efficient water management.
It expresses the volume of water consumed or contaminated in a fixed period of time, enabling the analysis of the environmental, social and economic implications of the use of water in different geographic contexts.
It is a quantitative indicator that reflects the direct and indirect use, consumption and contamination of water in 3 components: blue footprint, green footprint and grey footprint.
The concept and methodology for quantifying the WF were developed by Dr. Arjen Hoekstra in 2003 and were spread widely by the Water Footprint Network (WFN), which brings together international organisations working on water and sanitation issues since 2008.
The City Footprints Project bases its water footprint measurement methodologies on the following tool, both for organisations and cities:
Water Footprint Assessment Manual
The Water Footprint Assessment Manual, developed by the Water Footprint Network (WFN), provides a wide range of definitions and methods for water footprint accounting. It includes methods for assessing water sustainability and a range of options for responding to the results of these calculations. This manual represents a common standard for the definitions and assessment methods for water footprint calculations, as a basis for designing sustainable water management strategies and public policy making (WFN, 2004).
Volume of surface and groundwater consumed as a result of the production of a good or service. It is the amount of water abstracted from groundwater or surface water that does not return to the catchment from which it was withdrawn.
Volume of rainwater consumed during the production process. This is particularly relevant for agricultural and forestry products (products based on crops or wood), where it refers to the total rainwater evapotranspiration (from fields and plantations) plus the water incorporated into the harvested crop or wood.
The grey water footprint of a product is an indicator of the freshwater pollution associated with the supply chain. It is defined as the volume of freshwater that is required to assimilate the load of pollutants based on ambient water quality standards.
The use of water in urban areas is far from sustainable, even at current levels of demand. The evidence about climate change and its impacts on water resources show that the distribution of precipitation will change drastically and will become ever more erratic in the future, affecting the availability of water resources for human consumption, energy generation and agriculture, and hence likely affecting food security and sovereignty.
According to the FAO, water consumption has grown by more than double population growth in the last century. The demand for water could increase to 40% more than supply (McKinsey and Company, Charting our Water Future: Economic frameworks to Inform decision-making, 2009).
If we take into account the variable of water contamination (Grey WF), it is clear that the capacity of ecosystems to provide this vital resource is being drastically surpassed.
The evaluation of the water footprint makes visible how this resource is used by the environment, city economies, the daily production practices of the agricultural and industrial sectors, the daily habits of the population, and enables the true supply to be compared with the true demand, including water contamination. This evaluation process and the results obtained lead to an understanding of water as a common resource, thus promoting efficient management in cities with the involvement of relevant actors under a governance scheme.