Environmental Engineering Reference
In-Depth Information
The external water footprint is “the annual volume of water resources used in other coun-
tries to produce goods and services consumed by the inhabitants of the country” (Hoekstra and
Chapagain, 2007). In other words:
Volume of virtual water imports into the country
− Volume of virtual water exports to other countries
=
External water footprint
Then,
Internal water footprint
+
External water footprint
Water footprint of a nation
In addition:
Internal water footprint
Water self-sufficiency
=
Water footprint of a nation
A water self-sufficiency ratio of 1 means that a nation is capable of producing domestic
goods and services with water taken only from resources within the country's boundaries.
A ratio less than 1 implies that water demands are fulfilled by internal sources and water
imports as virtual water. When the ratio is zero, then 100 percent of the country's water needs
are met with virtual water imports (Chapagain and Hoekstra, 2004).
The water footprint for the whole world is estimated at 7.450 × 10
12
m
3
/year with an average
of 1,240 m
3
per person each year. Water footprint among countries varies significantly.
For instance China's water footprint is 700 m
3
per person each year and in the United States,
2,480 m
3
per person each year, which is a function of consuming patterns and diet—
meat consumption in the United States is three times the world's average (Hoekstra and
Chapagain, 2007).
Water footprint of a business
At a business level, water footprint can be calculated for the whole operation, for a particular
facility, or for individual products. When calculating the water footprint of a whole company
or a facility, the boundaries are automatically set by the limits of that entity. However, in the
case of products (especially food), it is important to set the boundaries to indicate at what level
the water footprint is computed. Figure 9.5 shows the water inputs at each step of the typical
supply chain for a food product. If the water footprint is calculated when the product reaches
the consumer (without including consumption), then the water footprint will incorporate all
the water used from the farmer to the retailer. If food preparation at home is also included,
then the consumer needs to be encompassed by the boundaries. In cases when food processors
want to know the water footprint of a particular product right before shipping to a distribution
center or a retailer, then the boundary would include only the steps upstream from the process-
ing facility.
The water footprint of a business has four components (Ercin et al., 2011):
1.
Operational water
, which is the water incorporated into the product, water consumed dur-
ing production (e.g., cleaning and washing bottles), and water polluted during the process.
