A grey water footprint larger than zero does not automatically imply that
ambient water quality standards are violated; it just shows that part of the
assimilation capacity has been consumed already. As long as the calculated
grey water footprint is smaller than the existing river flow or groundwater flow,
there is still sufficient water to dilute the pollutants to a concentration below
the standard. When the calculated grey water footprint is precisely equal to
the ambient water flow, then the resultant concentration will be exactly at the
standard. When the effluent contains a very high load of chemicals it may
happen that the calculated grey water footprint exceeds the existing river flow or
groundwater flow. In this case, pollution goes beyond the assimilation capacity
of the receiving water body. The fact that the grey water footprint can be larger
than the existing water flow illustrates that the grey water footprint does not
show ‘the polluted water volume’ (because one would not be able to pollute
a larger volume than the existing one). Instead, the grey water footprint is an
indicator of the severity of water pollution, expressed in terms of the freshwater
volume required to assimilate the existing load of pollutants