Environmental Engineering Reference
In-Depth Information
In China, the North China Plain Aquifer is a deep fossil aquifer that provides water for
agriculture, industries, and cities, including Beijing. A large amount of China's crops come from
this area. Because the aquifer is not rechargeable, once the water is depleted, all the activities that
once benefited from the aquifer will come to an end. A sign of an impending water crisis in that
area is reflected in the fact that wells need to be drilled to deeper and deeper levels (Brown, 2005).
WATER AND FOOD PRODUCTION
Virtual water
Virtual water (also known as imbedded water, embodied water, or exogenous water) is the
cumulative amount of water needed to produce any product or service. It is especially impor-
tant for agricultural products because they need large amount of water for their production.
The concept of virtual water makes countries exporting agricultural commodities “exporters
of water,” not in terms of real water that changes hands at the point of transaction but as the
cumulative water that was invested during production of a particular product. Similarly, coun-
tries with limited water resources that import agricultural products are not only importing the
commodities but also the virtual water attached to them (Chapagain and Hoekstra, 2004).
Estimation of virtual water in food products can be a difficult task. Factors to be considered in
the calculation are place and period of production, point of measurement (e.g., in irrigated crops
measured at field level or the point of water extraction), the production method, and method of
water allocation when intermediate products exist (Hoekstra, 2003, esp. Chapters 1, 3, and 15).
Virtual water is not just applied to agricultural products. Without exception all consumer
products need water at same point in the production chain (Table 9.4). Because production
Table 9.4
Average virtual water for selected consumer products.
Product
Virtual water content (liter)
1 glass of beer (250 mL)
75
1 glass of milk (200 mL)
200
1 cup of coffee (125 mL)
140
1 cup of tea (250 mL)
35
1 slice of bread (30 g)
40
1 slice of bread (30 g) with
90
1 potato (100 g)
25
1 apple (100 g)
70
1 cotton T-shirt (250 g)
2000
1 sheet of A4 paper (80 g/m
2
)
10
1 glass of wine (125 mL)
120
1 glass of apple juice (200 mL)
190
1 glass of orange juice (200 mL)
170
1 bag of potato crisps (200 g)
185
1 egg (40 g)
135
1 hamburger (150 g)
2400
1 tomato (70 g)
13
1 orange (100 g)
50
1 pair of shoes (bovine leather)
8000
1 microchip (2 g)
32
Reproduced from Hoekstra and Chapagain, 2007, with permission of Springer.
