Following the logic of the carbon footprint, the water footprint (WF) is related to the quantification of water. It “accounts for both the direct (domestic water use) and indirect (water required to produce industrial and agricultural products) water use of a consumer or producer” (Vanham and Bidoglio 2013). The WF is expressed in total volume of freshwater measured over the entire supply chain. “It is a multi-dimensional indicator, showing water consumption volumes by source and polluted volumes by type of pollution; all components of a total water footprint are specified geographically and temporally. The blue water footprint refers to consumption of blue water resources (surface and ground water) along the supply chain of a product. ‘Consumption’ refers to loss of water from the available ground-surface water body in a catchment area, which happens when water evaporates, returns to another catchment area or the sea or is incorporated into a product. The green water footprint refers to consumption of green water resources (rainwater stored in the soil as soil moisture). The grey water footprint refers to pollution and is defined as the volume of freshwater that is required to assimilate the load of pollutants based on existing ambient water quality standards” (Hoekstra et al. 2009, 8).

As with previously described methods and with the footprint methods in particular, there is also no consensus about the scope and exact accounting procedure of a WF, although there is an excellent manual called “The Water Footprint Assessment Manual: Setting the Global Standard” (Hoekstra et al. 2011) developed by the Water Footprint Network. Discrepancies in reported values may be due to authors not communicating their results according to the components of blue-, green- and grey water or researchers simply not following the proposed manual stringently enough (Harding 2019). Either way, the WF has so far not seen much application on a city scale as is evident from the small number of case studies.