Environmental Engineering Reference
In-Depth Information
Virtual
water
flow
Virtual
water
flow
Virtual
water
flow
Processing
plant
Farm
Retailer
Consumer
Real
water
use
Real
water
use
Real
water
use
Real
water
use
Figure 9.5
Real water input and virtual water flow in the food production chain.
From Hoekstra, 2008.
2.
Overhead operational water
is water consumed by employees, toilets, kitchen, plant
sanitation, working clothing, and landscaping.
3.
Supply-chain water related to product inputs
, which includes water used to produce ingre-
dients other than water added to the food product and water used to produce packaging
material.
4.
Overhead supply-chain water
includes but is not limited to water that has been used to
construct buildings, equipment used in the plant and offices, transportation, and energy
generation.
Each of the four components contains water consumption as green and blue water and waste-
water production as grey water (Ercin et al., 2011).
Water footprint of agricultural products
The calculation of the water footprint of agricultural products is based on typical water
needs for particular crops in ideal conditions with models such as the ones developed by the
Food and Agriculture Organization (1998). The consumption of water in
m
3
/
hectare
divided
by the yield for a particular field in
tonnes/hectare
will provide the water consumption in
m
3
/
tonne
. Table 9.5 presents the average content of virtual water for selected agricultural
products.
For animal products, water footprint is calculated by accounting all the water directly drank
by the animal plus the virtual water consumed with feed during its lifetime (Hoekstra, 2008).
When different products come out of agricultural or animal products (e.g., chickens produce
meat for human consumption, by-products that are transformed into protein meals, and fat that
is used as animal feeds), then the total water footprint needs to be allocated to the different
fractions. Hoekstra and Chapagain (2008) suggest the use of mass as allocation criterion;
however, depending on the situation, allocation can be done according to other criteria such as
energy content or economic value (more about allocation is found in Chapter 4).
Water neutrality
Water neutrality is a concept that has been developed as a way of motivating companies
and individuals to reduce water consumption and compensate for their impact (Hoekstra,
2008). It can be seen as a similar concept to offsetting carbon emissions by supporting projects
in renewable energy. In the case of water, the offsetting may come from investing in improving
