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A dwindling river: as water demands rise, the Colorado River is running dry.

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About 100 years ago, the Colorado River raged southward toward the Gulf of California. Where the two water bodies met, great walls of water once sprayed into the sky. But these spectacular events no longer occur. These days, the Colorado River often dries up before it even reaches the Gulf of California.

The Colorado River is shrinking, as are many of the world's fresh water sources. People are draining away huge quantities of water for personal use, such as for drinking and bathing. Agricultural and industrial uses are depleting even more of our supply of fresh water. For instance, water is used in the manufacture of goods like cotton T-shirts and paper. People are tapping into Earth's fresh water at an unsustainable rate, says Eleanor Sterling, curator of the exhibition Water: [H.sub.2]O = Life, which highlights water's many forms and uses, at the American Museum of Natural History in New York City. As the world's population grows, the demand for this precious liquid is increasing. "Ensuring that everyone has enough fresh water will be one of the major issues facing us this century," says Sterling.

WATER PRESSURE

Roughly 70 percent of Earth's surface is covered by water; so how can the planet's supply be at risk of falling short of our needs? More than 97 percent of Earth's water is salt water. The remainder is fresh water, most of which is frozen in ice caps and glaciers or is situated deep beneath Earth's surface. Only a tiny fraction of fresh water is currently available for use.

In addition, freshwater sources are spread extremely unevenly around the globe. Water shortages are greatest in and regions like southern Africa and the southwestern United States. Plus, populations in many of these regions are rapidly increasing, stretching already limited water supplies even thinner.

Phoenix, Arizona, is one of these areas. The region is home to approximately 3 million people, and thousands of new residents are pouring into the region each year. Yet the city--located in the middle of the dry Sonoran Desert--receives fewer than 25 centimeters (10 inches) of rain annually. That amount of precipitation is roughly one third the national average.

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WATERING THE DESERT

So how do people in the Southwest quench their thirsts, grow acres of crops, and still leave enough water for wildlife? Groundwater, or underground water that is stored in the tiny spaces in soil, sand, gravel, and rock, provides one source of fresh water. But there isn't enough groundwater to meet all of the demands. The bulk of the water comes from the Colorado River (see map, right).

The 2,334 kilometer (1,450 mile)-long river supplies water to several big cities, including Las Vegas and San Diego. In all, it delivers fresh water to roughly 30 million people. But much of the water, about 80 percent, is used to irrigate millions of acres of farmland.

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SOUTHWEST DISTRESS

The demand for water is taking a toll on the river. Except in heavy-flood years, dams and canals capture every drop of the Colorado River for use. As the region's population grows, the river is becoming unable to provide enough water for everyone's needs.

Overuse of the Colorado River threatens water supplies to homes and to ranchers and farmers, who provide food for the nation. But the drying of the river has also taken its toll on plants and animals in ecosystems along the river. The Colorado River Delta, where the river meets the sea, was once a fertile region teeming with life. But so little of the water reaches the delta now that bobcats, beaver, and many fish species have lost suitable habitat. To restore this important habitat, people will have to learn to live comfortably with less water, says Sterling.

"To tackle the problem of water shortages, the focus should be on conservation--how to live with less of it," says Sterling. People in the U.S. use more water than most other people in the world. Most of that water is used for agricultural purposes (see graphs, below).

Aiming to decrease our thirst for water, scientists are developing new conservation methods. "In places like the Southwest, large amounts of water [used on crops] can be lost to evaporation," says Sterling. To limit evaporation, scientists are studying irrigation techniques that would deliver water directly to a plant's roots. Individuals and communities are trying to develop solutions too, like planting drought-tolerant gardens.

PERSONAL DECISIONS

When it comes to conserving water, everyone can make a difference. For instance, says Sterling, choose your food wisely: Everything you eat needs water at some point. Which do you suppose requires more water to produce: a slice of watermelon or a hamburger? An entire watermelon requires 400 liters (100 gallons) of water, while a quarter-pound hamburger needs 27 times as much. How can that possibly be? A lot of grain has to be watered to feed the cow, explains Sterling.

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Other ways to conserve may be more surprising. Bottled water, which is so popular among consumers, actually has environmental pitfalls, says Sterling. That's because it depletes water from one location by distributing it to another, and a huge amount of energy is used to produce and transport the bottles. Sterling recommends using refillable bottles instead.

Water is also needed to manufacture many goods like computer chips in cell phones, cameras, and toys. By buying only what you need, you will save money and help to protect the planet's water supply.

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PERCENT OF WORLDWIDE
WATER USAGE, BY SEGMENT

Household
activities, such
as bathing and
washing dishes,
account for less
than 10 percent
of fresh-water
usage. Which
segment
accounts for the
most usage?

Household 8%
Industrial 22%
Agricultural 70%

PERCENT OF HOUSEHOLD
WATER USAGE, BY ACTIVITY

The typical
household in
an industrialized
country uses more
water for bathing
and showering
than for any other
activity. How
could you greatly
reduce your
household water
consumption?

Cleaning 5%
Bathing and Showering 35%
Flushing Toilet 30%
Laundry 20%
Cooking and Drinking 10%


check it out

Earth's surface is nearly three-quarters water. So why should you care about saving a few gallons here or there? Every drop counts. Even in places where it rains a lot, water conservation ensures that there is enough for humans and wildlife alike.

Water: [H.sub.2]O = Life is a new exhibition opening November 3, 2007, at the American Museum of Natural History. In it, you can explore the mystery and necessity of water-and how you can help conserve this vital resource.

To learn more, ask your teacher, or visit www.amnh.org. You can also visit http://ology.amnh.org.

PRE-READING PROMPT

* What factors could lead to a shortage of fresh water in the United States?

DID YOU KNOW?

* According to the United Nations Environment Programme, groundwater aquifiers provide 50 percent of global drinking water.

CRITICAL THINKING:

* Desalination plants remove salt from ocean water to make fresh water. What are some pros and cons of using this technology? (For possible answers, read the story found on this Web site: http://news.bbc.co.uk/2/hi/science/nature/6767533.stm)

CROSS-CURRICULAR CONNECTIONS:

MUSIC: Many cultures around the world use water to create music. Do research and write a report on a water-based musical instrument.

RESOURCES

* For teaching materials about conserving the Colorado River, visit this Web Site: www.crwcd.org/page_104

* "Test Your WaterSense" is a game that quizzes kids on water usage. Find it at: www.epa.gov/watersense/quiz/index.htm

1. Roughly--percent of Earth's surface is covered by water. More than 97 percent of Earth's water is--. The remainder is--.

2.--is underground water that is store(t in the tiny spaces in soil,--gravel, and

3. A--is the area where a river meets the sea.

4. About--of the water that flows from the Colorado River is used to irrigate millions of acres of--.

5.--is responsible for the largest percent of worldwide water usage. It accounts for --percent. People in this country use more water than people anywhere else in the world: --.

ANSWER

1. 70: salt water: fresh water 2. Groundwater, sand, rock 3. delta 4. 80 percent, farmland 5. Agriculture: 70: United States
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Title Annotation:EARTH WATER
Author:Jango-Cohen, Judith
Publication:Science World
Date:Oct 8, 2007
Words:1367
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