Integration over time and different pollutants
Daily values for the grey water footprint can be added over the year to get annual
values. When a waste flow concerns more than one form of pollution, as is
generally the case, the grey water footprint is determined by the pollutant that
is most critical, that is the one that is associated with the largest pollutantspecific
grey water footprint. For the purpose of finding an overall indicator
of water pollution, the grey water footprint based on the critical substance is
sufficient. If one is interested in the pollutant-specific grey water footprints, one
can of course report those values separately. For formulating response measures
targeted at specific pollutants, this is of course very relevant. For the overall
picture of pollution, however, showing the grey water footprint for the critical
substance is good enough.