chemicals discharged into a water body (Effl × ceffl) will be equal or larger than the
amount abstracted chemicals (Abstr × cact), so the load is positive. In exceptional
circumstances (either because ceffl < cact or because Effl < Abstr), one could
calculate a negative load, which has to be neglected for water footprint accounts
(so one should account for a zero water footprint in such a case). The positive
contribution made to the environment in the exceptional case of a ‘negative load’
is to be appreciated but should not be counted in the water footprint accounts, in
order to separate the discussion of possible water footprint compensation from
existing positive water footprints. Water footprint compensation or ‘offsetting’
is a debate in itself (see Box 5.2 in Chapter 5), which should be held and made
explicit, not hidden in the accounts. It is further to be noted that, when water
for a certain process is abstracted in catchment A while the effluent is discharged
into catchment B, one should take Abstr = 0 for the calculation of the grey water
footprint in catchment B.