Environmental Engineering Reference
In-Depth Information
feet, so considerable lifting of water would be necessary to tap into the
Great Lakes, in addition to the pipelines that would need to be laid.
Pumping water over the land is energy intensive, and pumping it to
higher elevations is even more energy intensive. About 20 percent of
California's energy is used to move water from the wetter north to the
drier south.
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A novel method for obtaining water has been pioneered by a fi rm in
Israel that has developed a machine that extracts water from the humid-
ity in the air. The method uses a solid desiccant to absorb the moisture
and an energy-saving condenser that reuses more than 85 percent of the
energy input to the system.
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The cost of the water is similar to water
produced by desalination.
Virtual Water: Now You See It, Now You Don't
Virtual water
is an economic concept referring to the amount of water
consumed in the production of an agricultural or industrial product. A
person's water footprint is the total amount of freshwater consumed in
the production of the goods and services that that individual consumes.
Virtual water is a hidden part of a person's water use. The water is said
to be virtual because once the grain is grown, beef produced, jeans fab-
ricated, or automobile manufactured, the real water used to grow it is
no longer actually contained in the product as water. It has been con-
sumed or transformed into other chemicals and cannot be recycled or
recovered (table 1.3).
Each person's water footprint is determined largely by eating habits.
Vegetarians have a lower water footprint than omnivores because of the
large amount of virtual water needed to produce meat and associated
dairy products. Producing a pound of corn, wheat, or potatoes requires
only 30 to 160 gallons of water; beef, however, can require almost 1,900
gallons (fi gure 1.4). The 10 percent of Americans who do not own cars
and families with fewer cars have lower water footprints than those who
are more affl uent. The water footprint of the United States is about 700
gallons per year per person, about double that in the United Kingdom.
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Nations with shortages of freshwater should not compound their
problem by producing and exporting products that require large amounts
of water in their production. For example, in Israel, a nation that is
mostly arid to semiarid and where water shortages are common, the
export of oranges has been discouraged since the 1980s because it is a
relatively thirsty crop and it makes no sense to send Israel's water to
