Water recycling and reuse are often used as two interchangeable terms. Here
we define ‘water recycling’ specifically as the on-site reuse of water for the same
purpose and ‘water reuse’ as the reuse of water elsewhere, possibly for another
purpose. In the case of recycling, we can make an additional distinction between
recycling of wastewater (by treating it for reuse) and recycling of evaporated
water (by condensing water vapour for reuse). The different sorts of water
recycling and reuse are shown for a simple example in Figure 3.5. The figure
shows two processes, the second of which reuses (treated) wastewater from the
first. The scheme shows that for the blue water footprints of both processes it
is the consumptive water use (evaporation and incorporation into products)
that counts. Water recycling and reuse can be instrumental in reducing the blue
water footprint of a process only when it effectively reduces consumptive water
use. Water recycling and reuse may also be instrumental in reducing the grey
water footprint of water users, but this will be discussed in Section 3.3.3.