Page 241 - Materials Chemistry, Second Edition

4.5 Impact Categories, Impact Indicators and Characterisation Factors 225

especially rivers, to flows. The latter is true only in case of a plentiful supply or of
use not followed by consumption (e.g. as cooling water).
As water is already regionally traded, though not yet worldwide, and shows
extremely inhomogeneous local distribution, a global reference basis (as in
Equation 4.8) does usually not make sense. Already within relatively homoge-
neous economic areas (EU, USA) extreme differences in the available fresh water
supply occur, so that only a regional view is applicable. This requires a suffi-
ciently elaborate LCI and also includes a definition of use or ‘consumption’ of this
resource. Consumption mostly consists in the use of water with contamination,
which makes it useless for further use, for example, as drinking water, another loss
being evaporation (especially during irrigation). Water purification belongs to the
end-of-life of many product systems and can be regarded as resources recovery.
The inclusion of water use seems particularly important in view of LCAs where
geographical system boundaries of countries, respectively, to regions with scarce
clean fresh water supply are included. The resource types (e.g. surface water (river,
lake), fossil and non-fossil groundwater, precipitation) considered and the forms of
water use (e.g. drinking, cooling, irrigation) must be defined. The volume of water
considered depends on whether only the so-called blue water (surface water and
groundwater) is included or the so-called green water (precipitate and soil moisture
that is evaporated by plants) is also included. The volume of water calculated for the
production of, for example, 1 kg wheat will differ significantly. Hence, particular
attention must be paid when comparing LCA results and not exactly the same LCI
and LCIA methods have been used.
The quantification of water scarcity can principally be done according to
Equation 4.8, albeit under consideration of water withdrawal and regional availabil-
ity of fresh water supply (withdrawal-to-availability ratio – WTA). Regional reserves
of the special case as well as formation rates for all used water categories are
to be determined. Regarding the availability of fresh water supply a recourse to
data banks is possible, for example, WaterGAP2. 120) An approach to include water
scarcity is also included in the Swiss ecoscarcity model. 121)
The inclusion of water as a resource is essential whenever consumption exceeds
the formation rate (R > 0 in Equation 4.9), or if different uses compete, for
i
example, irrigation in agriculture, drinking water or water supply to a humid
biotope (wetlands).
A comprehensive survey of water as a resource in the context of the impact
estimation has been elaborated by a working group of the UNEP/SETAC Life Cycle
Initiative. 122) An aspect that has so far been neglected was considered: often (fresh)
water is not only a scarce resource for humans but also essential to the life of
all organisms. It therefore serves a more substantial function than the resources
discussed above, all fossil and most mineral resources being of interest to humans
only or at least predominantly. In this function, water belongs to a protected

120) Alcamo et al. (2003).
121) Frischknecht et al. (2009).
122) Koellner and Scholz (2008) and Koellner and Geyer (2013).