Environmental Engineering Reference
In-Depth Information
Taking Out the Salt
The ocean holds 97 percent of the earth's water, but its salinity renders
it unusable for drinking and for most other uses. It contains about 35,000
parts per million (ppm) of dissolved materials (3.5 percent). The EPA's
guideline for drinking water recommends a maximum of 500 ppm; most
drinking water in the United States contains 100 ppm or less. Expensive
technology is required to make seawater potable, but the benefi t is incal-
culable: an unending supply of freshwater. As one water specialist has
said, “When you're running out of water, you don't care about what the
energy bill is.” The world's largest desalination plant opened in Ashkelon,
Israel, on the Mediterranean Sea coast in 2005; it supplies 5 to 6 percent
of the nation's demand and 13 percent of domestic consumer needs.
29
Freshwater produced by desalination of seawater costs two to three
times more than water obtained by conventional water treatment, but
water is so cheap in the United States that doubling or even tripling the
cost is something most Americans can easily bear. At present, desalina-
tion's contribution to the total U.S. water supply is negligible. There were
about 250 desalination plants in the United States in 2005 and every
state has at least one, but they have the capacity to provide less than 0.4
percent of the water used in the United States, and most of this water is
used by industries, not municipalities.
30
Florida has nearly half of the
plants, with Texas and California in second and third place.
Most of the existing plants are designed to handle brackish water
(1,000-10,000 ppm) rather than seawater, and cost about half as much
money to build. Brackish water is present at depths of less than 500 feet
over about half of the conterminous United States (fi gure 1.6) and is a
large potential source of water that has not been tapped.
The Bureau of Reclamation forecasts that by 2020, desalination tech-
nologies will contribute signifi cantly to ensuring a safe, sustainable,
affordable, and adequate water supply for the nation.
31
The ability to
make ocean water potable guarantees an inexhaustible water supply,
albeit at prices higher than Americans are used to paying. Desalination
is an inevitable part of America's water future.
Poisoning Our Water
Americans are making a two-pronged attack on their water supply. Not
only do they use it extravagantly and wastefully, but they pour harmful
chemicals in it as well.
32
In 2007, 232 million pounds of toxic chemicals
