2.2. Green water footprint (WFgreen)
In conventional WWTPs, the green WF is not considered
because it does not promote the evaporation of water from the soil
or from vegetables and does not promote the incorporation of soil
water with treated water.
2.3. Grey water footprint (WFgrey)
The proposed calculation for the grey water footprint in the
WFA manual (Hoekstra et al., 2011) has been adapted to the specific
domain of WWTPs. The new equation is based on a mass balance at
the WWTP discharge point (see Equations (2) and (3) and Fig. 2).
This mass balance-based approach considers that the grey WF is
the minimum volume of water required to dilute the pollutant