Water and Water Pollution - Environmental Science - page 248

Bottom line: Currently, significant desalination is
practical only for wealthy and water-short countries
and cities that can afford its high cost.
Scientists are working to develop new membranes
for reverse osmosis that can separate water from salt
more efficiently and under less pressure. If successful,
this strategy could bring down the cost of using desali-
nation to produce drinking water. Even so, desalinated
water probably will not be cheap enough to irrigate
conventional crops or meet much of the world's de-
mand for fresh water unless scientists can figure out
how to use solar energy or other means to desalinate
seawater cheaply and how to safely dispose of the salt
left behind.

in arid and semiarid areas, stimulate local economies,
and help keep the prices of food, manufactured goods,
and electricity low.
Most water resource experts believe that when
water scarcity afflicts many areas in this century, gov-
ernments will have to make the unpopular decision to
raise water prices. China did so in 2002 because it
faced water shortages in most of its major cities, rivers
running dry, and falling water tables in key agricul-
tural areas.
Higher water prices encourage water conserva-
tion but make it difficult for low-income farmers and
city dwellers to buy enough water to meet their needs.
South Africa has found a novel solution to this prob-
lem. When the country raised water prices, it estab-
lished lifeline rates that give each household a set
amount of water at a low price to meet basic needs.
When users exceed this amount, the price rises.
The second major cause of water waste is lack of
government subsidies for improving the efficiency of water
use. A basic rule of economics is that you get more of
what you reward. Withdrawing subsidies that encour-
age water waste and providing subsidies for efficient
water use would sharply reduce water waste.

11-3 REDUCING WATER WASTE

Economics: Benefits of Reducing
Water Waste
We waste about two-thirds of the water we use, but
we could cut this waste to 15%.
Mohamed El-Ashry of the World Resources Institute
estimates that 65-70% of the water people use throughout
the world is lost through evaporation, leaks, and other
losses. The United States, the world's largest user of
water, does slightly better but still loses about half of
the water it withdraws. El-Ashry believes it is econom-
ically and technically feasible to reduce such water
losses to 15%, thereby meeting most of the world's wa-
ter needs for the foreseeable future.
This win-win solution would decrease the burden
on wastewater plants and reduce the need for expen-
sive dams and water transfer projects that destroy
wildlife habitats and displace people. It would also
slow depletion of groundwater aquifers and save both
energy and money.
According to water resource experts, the main
cause of water waste is that we charge too little for water.
Such underpricing is mostly the result of government
subsidies that provide irrigation water, electricity, and
diesel fuel for farmers to pump water from rivers and
aquifers at below-market prices.
Because these subsidies keep the price of water
low, users have little or no financial incentive to invest
in water-saving technologies. According to water re-
source expert Sandra Postel, “By heavily subsidizing
water, governments give out the false message that it
is abundant and can afford to be wasted—even as
rivers are drying up, aquifers are being depleted, fish-
eries are collapsing, and species are going extinct.”
Farmers, industries, and others benefiting from
government water subsidies offer a counter-argument:
They promote settlement and agricultural production

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H OW W OULD Y OU V OTE ? Should water prices be raised
sharply to help reduce water waste? Cast your vote online at
http://biology.brookscole.com/miller11.

Solutions: Wasting Less Water
in Irrigation
Although 60% of the world's irrigation water is
currently wasted, improved irrigation techniques
could reduce this proportion to 5-20%.
About 60% of the irrigation water applied throughout
the world does not reach the targeted crops and does
not contribute to food production. Most irrigation sys-
tems obtain water from a groundwater well or a sur-
face water source. The water then flows by gravity
through unlined ditches in crop fields so the crops can
absorb it (Figure 11-17, left). This flood irrigation method
delivers far more water than is needed for crop growth
and typically loses 40% of the water through evapora-
tion, seepage, and runoff.
More efficient and environmentally sound irriga-
tion technologies can greatly reduce water demands
and waste on farms by delivering water more pre-
cisely to crops. For example, the center-pivot low-
pressure sprinkler (Figure 11-17, right) uses pumps to
spray water on a crop. Typically, it allows 80% of the
water to reach crops. Low-energy precision application
(LEPA) sprinklers, another form of center-pivot irriga-
tion, put 90-95% of the water where crops need it by