humans and the water supply

water shortages

Water shortages are common in much of the world. People are most likely to run short of water during droughts. A drought is a period of unusually low rainfall. Human actions have increased how often droughts occur. One way people can help to bring on drought is by cutting down trees. Trees add a lot of water vapor to the air. With fewer trees, the air is drier and droughts are more common. We already use six times as much water today as we did a hundred years ago. As the number of people rises, our need for water will grow. By the year 2025, only half the worlds people will have enough clean water. Water is such a vital resource that serious water shortages may cause other problems. Crops and livestock may die, so people will have less food available. Other uses of water, such as industry, may have to stop. This reduces the jobs people can get and the products they can buy. People and nations may fight over water resources. In extreme cases, people may die from lack of water. The Figure 21.7 shows the global water situation in the 2030s with water stress and water scarcity on the map.

water problems poor quality water

The water Americans get from their faucets is generally safe. This water has been treated and purified. But at least 20 percent of the worlds people do not have clean drinking water. Their only choice may be to drink water straight from a river (see Figure 21.8). If the river is polluted with wastes, it will contain bacteria and other organisms that cause disease. Almost 9 out of 10 cases of disease worldwide are caused by unsafe drinking water. Diseases from unsafe drinking water are the leading cause of death in young children.

wealth and the water supply

Richer nations can drill deep wells, build large dams or supply people with water in other ways. In these countries, just about everyone has access to clean running water in their homes. Its no surprise that people in these countries also use the most water. In poorer nations, there is little money to develop water supplies. Look at the people in Figure 21.6. These people must carry water home in a bucket from a distant pump.

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rainfall and the water supply

Rainfall varies around the globe. About 40 percent of the land gets very little rain. About the same percentage of the worlds people dont have enough water. You can compare global rainfall with the worldwide freshwater supply at the two URLs below. Drier climates generally have less water for people to use. In some places, people may have less water available to them for an entire year than many Americans use in a single day! How much water is there where you live? Global rainfall: http://commons.wikimedia.org/wiki/File:World_precip_annual.png Freshwater supply: http://commons.wikimedia.org/wiki/File:2006_Global_Water_Availability.svg

water in industry

Almost a quarter of the water used worldwide is used in industry. Industries use water for many purposes. Chemical processes need a lot of water. Water is used to generate electricity. An important way that industries use water is to cool machines and power plants.

water in agriculture

Many crops are grown where there isnt enough rainfall for plants to thrive. For example, crops are grown in deserts of the American southwest. How is this possible? The answer is irrigation. Irrigation is any way of providing extra water to plants. Most of the water used in agriculture is used for irrigation. Livestock also use water, but they use much less. Irrigation can waste a lot of water. The type of irrigation shown in Figure 21.2 is the most wasteful. The water is sprayed into the air and then falls to the ground. But much of the water never reaches the crops. Instead, it evaporates in the air or runs off the fields. Irrigation water may cause other problems. The water may dissolve agricultural chemicals such as pesticides. When the water soaks into the ground, the dissolved chemicals do, too. They may enter groundwater or run off into rivers or lakes. Salts in irrigation water can also collect in the soil. The soil may get too salty for plants to grow.

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how we use water

Figure 21.1 shows how people use water worldwide. The greatest use is for agriculture and then industry. Municipal use is last, but is also important. Municipal use refers to water used by homes and businesses in communities.

where is all the water

One problem is that only a tiny fraction of Earths water is fresh, liquid water that people can use. More than 97 percent of Earths water is salt water in the oceans. Just 3 percent is freshwater. Most of the freshwater is frozen in ice sheets, icebergs, and glaciers (see Figure 21.5).

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water problems not enough water

Most Americans have plenty of fresh, clean water. But many people around the world do not. In fact, water scarcity is the worlds most serious resource problem. How can that be? Water is almost everywhere. More than 70 percent of Earths surface is covered by water.

water for fun

There are many ways to use water for fun, from white water rafting to snorkeling. When you do these activities you dont actually use water. You are doing the activity on or in the water. What do you think is the single biggest use of water for fun? Believe it or not, its golf! Keeping golf courses green uses an incredible amount of water. Since many golf courses are in sunny areas, much of the water is irrigation water. Many golf courses, like the one in Figure 21.4, have sprinkler systems. Like any similar sprinkler system, much of this water is wasted. It evaporates or runs off the ground.

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household uses of water

Think about all the ways people use water at home. Besides drinking it, they use it for cooking, bathing, washing dishes, doing laundry, and flushing toilets. The water used inside homes goes down the drain. From there it usually ends up in a sewer system. At the sewage treatment plant, water can be is treated and prepared for reuse. Households may also use water outdoors. If your family has a lawn or garden, you may water them with a hose or sprinkler. You probably use water to wash the car, like the teen in Figure 21.3. Much of the water used outdoors evaporates or runs off into the gutter. The runoff water may end up in storm sewers that flow into a body of water, such as the ocean.

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instructional diagrams

No diagram descriptions associated with this lesson

questions

Regarding water use, developing nations use

a. a greater percentage for industry.

-->  b. more for agriculture than for industry.

c. more for household uses than any other category.

d. a greater percentage for agriculture.

Municipal use of water refers to water that is used for

a. manufacturing.

b. growing crops.

c. raising livestock.

-->  d. none of the above

Irrigation water may cause

a. soil to become too salty for plants.

b. pesticides to enter groundwater.

c. a lot of water to be wasted.

-->  d. all of the above

Recreational uses of water include

a. irrigating golf courses

b. kayaking

c. scuba diving

-->  d. all of these

Almost a quarter of the water used worldwide is used by

a. farms.

-->  b. factories.

c. businesses.

d. households.

Agricultural chemicals

-->  a. may enter groundwater

b. evaporate into the air

c. stay on the plants they target

d. all of these

Water is lost for human use if it

a. infiltrates into the ground

b. enters a stream

-->  c. becomes polluted

d. all of these

In industry, water is used for

a. cooling machines.

b. chemical reactions.

c. purifying municipal sewage.

-->  d. two of the above

The main cause of disease and death in young children worldwide is

a. food scarcity.

b. water scarcity.

-->  c. water pollution.

d. none of the above

The amount of water available to a population depends on

a. rainfall

b. the money available to develop water supplies

c. political agreements

-->  d. all of these

Which of the following human actions increases the risk of drought?

-->  a. cutting down trees

b. irrigating farmland

c. building golf courses

d. polluting water with wastes

A lot of irrigation water is wasted because it

a. evaporates in the air.

b. runs off the field.

c. soaks into the soil.

-->  d. two of the above

All forms of life need water to survive.

-->  a. true

b. false

We can live longer without water than we can without food.

a. true

-->  b. false

Irrigation may add unwanted chemicals to groundwater.

-->  a. true

b. false

Large irrigation systems may waste a lot of water.

-->  a. true

b. false

Water can be used to generate electricity.

-->  a. true

b. false

Water scarcity is not a problem since 70% of Earth is covered by water.

a. true

-->  b. false

More than 70 percent of Earths surface is covered with water.

-->  a. true

b. false

Glaciers are a source of fresh water in some locations.

-->  a. true

b. false

Most people in the world have enough clean fresh water.

a. true

-->  b. false

Most of the fresh water on Earth is under the ground.

a. true

-->  b. false

By the year 2025, only one-quarter of the worlds people will have enough clean water.

a. true

-->  b. false

In poorer countries, many young children die from waterborne diseases.

-->  a. true

b. false

Drier climates generally have less water for people to use.

-->  a. true

b. false

Because of conservation, we use less water today than we did a century ago.

a. true

-->  b. false

Water is safe to drink as long as it is moving water.

a. true

-->  b. false

worlds most serious resource problem

a. agriculture

b. irrigation

c. storm sewer

d. drought

-->  e. water scarcity

f. water quality

period of unusually low rainfall

a. agriculture

b. irrigation

c. storm sewer

-->  d. drought

e. water scarcity

f. water quality

degree to which water is polluted

a. agriculture

b. irrigation

c. storm sewer

d. drought

e. water scarcity

-->  f. water quality

any method of providing extra water to plants

a. agriculture

-->  b. irrigation

c. storm sewer

d. drought

e. water scarcity

f. water quality

underground pipe that collects runoff water

a. agriculture

b. irrigation

-->  c. storm sewer

d. drought

e. water scarcity

f. water quality

greatest use of water worldwide

-->  a. agriculture

b. irrigation

c. storm sewer

d. drought

e. water scarcity

f. water quality

diagram questions

No diagram questions associated with this lesson