Although over 70% of Earth's surface is covered with water, less than 1% of this water is available for human consumption. In this lesson, students study the availability of water on Earth and discuss methods that can be used to purify and conserve this critical resource. They also assess how much water they and their families typically use, and think about ways to reduce their water usage. Finally, students explore different techniques being employed for water management around the world, including the use of dams to create reservoirs.
- Identify sources of fresh water available for consumption
- Understand the need for water conservation due to the limited fresh water supply
- Explore strategies for conserving water at home
- Compare the benefits and drawbacks of using different water management techniques, particularly dams
Grade Level: 6-8
Two to three class periods
- Global Water Distribution Flash Interactive
- Water Treatment Plant QuickTime Video
- Conserving Water at Home QuickTime Video
- Water Conservation: Israel QuickTime Video
- Water Conservation: Mexico QuickTime Video
- Water Conservation: Denver, CO QuickTime Video
- Two 2-liter bottles full of water
- Food coloring (dark color preferable)
- Measuring cups (for measuring amounts ranging from 50 ml to 14.5 ml)
- Five clear containers (to hold water ranging in volume from 1,950 ml to 0.5 ml)
- Markers and tape for making labels
- Map of your local watershed (See Surf Your Watershed for maps)
- Water Use Worksheet PDF Document
- Notebooks for student work
Before the Lesson
- Fill two 2-liter bottles with water. Add enough food coloring so that the water is visible from all seats in the classroom.
- Prepare to lead the class in a discussion about your local watershed by researching the following:
- How does water get to the school? (Where does it originate? What path does it travel?)
- How is the water managed along the way?
- How is the water treated once it leaves your school as wastewater?
- Where are the water treatment plants?
- Are there any dams? If so, where are they located?
Part I: How Much Water Do We Really Have?
1. Tell students that you would like them to think about the answer to this question: What percentage of Earth's water is available for human consumption? Ask students to write down their answers. You may want to remind students to consider what they know about oceans and about the type of water that is considered usable by people.
2. Ask a volunteer to demonstrate his or her answer to the question. Give the student a 2-liter bottle filled with colored water and a clear, empty container. Tell the class that the bottle represents all of the water on Earth. Ask the volunteer to pour into the empty container the amount of water that he or she thinks represents the percentage of Earth's water available for human use. (Provide the student with a measuring cup if needed.) Then ask the class to make suggestions about whether more or less water needs to be in the container. Have the volunteer adjust the amount until there is a general consensus among the students. Put the class estimate (the clear container with water) aside.
3. Tell students that you will now demonstrate the amount of water on Earth that is available for human consumption.
- Show students the second 2-liter bottle filled with colored water. Tell them that this bottle again represents all of the water on Earth. Measure out 1,950 ml of the water and pour it into a clear, empty container. Label the container SALT WATER. Tell students that this represents how much of our planet's water is found in oceans — 97%.
- Pour the remaining 50 ml from the bottle into another container, and tell students that this represents the amount of fresh water on Earth — 3%. Label this container FRESH WATER. Ask students to guess what percentage of fresh water is available for human use.
Note: You may also want to place a fresh water sign on the table at this time. As you pour off additional amounts of water in steps c-d, you can place the new containers near the fresh water sign to remind students that each one is part of the "fresh water" category.
- Measure 35 ml of the fresh water into another container. Label the container ICE CAPS. Tell students that this water is frozen in ice caps, so it is not available for our use!
- Now measure 14.5 ml of the fresh water into another container. Label the container AIR, SOIL, AND UNDERGROUND. Tell them sorry, but this water is found in the air, in the soil, and deep underground, so it's also not available for human use!
- There should be about 0.5 ml of water left in the fresh water container. (Note that this is just under two drops of water!) Hold this up and explain that this represents all of the fresh water available for human use. Less than 1% of all water on Earth is available for consumption!
- Show students the Global Water Distribution Flash Interactive to reinforce the data behind the demonstration.
4. Divide the class into small groups and ask them to discuss what they just witnessed in your demonstration and in the interactive activity. (You may want to review the terms renewable resource and nonrenewable resource as a class before placing students into their groups.) Have students answer the following questions during their small-group discussions:
- Where is usable water located?
- Is this water a renewable resource?
5. Bring the class back together and ask student groups to share some of their ideas. Conclude by reminding students that water is necessary for life and thus important to conserve and maintain so that it stays available for human consumption, as well as for consumption by plants and animals, which people use for food.
Part II: Where Does Your Water Come From?
6. Watch the Water Treatment Plant QuickTime Video and discuss the methods used to purify water for human consumption. Ask students the following questions:
- Why is it important to treat the water before sending it to homes?
- What do you think the brown sludge is made of? What other things do you think are removed from water to make it safe for drinking?
7. Show the map of your local watershed. Help students trace the path of water to their school. Discuss the following questions:
- Where does the water originate and how is it managed along the way?
- How is the water treated after it leaves the school as wastewater?
- Where do you think the water treatment plants are located?
Part III: How Much Water Do You Use Per Day?
8. Distribute the Water Use Worksheet PDF Document, and ask students to estimate the amount of water that they and their families typically use in a week.
9. Watch the Conserving Water at Home QuickTime Video. Discuss water conservation techniques that people can use to decrease the waste and pollution of our water resources. Consider the following questions:
- An average family uses about 300 gallons of water per day. What are some of the best ways to conserve water?
- What is "gray water" and how can it be used to help conserve water?
- What is Xeriscape landscaping and how can it help conserve water?
10. Divide the class into small groups again and ask them to brainstorm ways that they and their families can conserve water. After the small-group discussions, bring the class back together and ask each group to share their top three ideas with the class.
Part IV: Managing the Water Supply
11. Increases in population and industrial growth are straining water resources around the world and making the need for water management more urgent. Show students the Water Conservation: Israel QuickTime Video and the Water Conservation: Mexico QuickTime Video. Discuss the following questions:
- What water problems are faced by Israel? By Mexico?
- What water conservation techniques does each country use?
- What are some unanticipated consequences of each of these techniques?
12. Divide the classroom into two groups. Assign one group to develop arguments in support of the use of dams to manage water for large cities. Assign the other group to develop arguments against it. Show the Water Conservation: Denver, CO QuickTime Video, and then have the two groups debate the pros and cons of using dams.
13. Show the class the local watershed map again and label the location of any dams in the area. Discuss the following questions:
- How might the dams be changing the natural environment in this area?
- What conservation techniques can be used to help the natural ecosystem survive population increases?
- Invite a guest speaker from the local water conservation department to come to your class and provide detailed information about the process of getting water to students' homes and school, the use of dams and/or reservoirs for water storage, whether or not gray water is collected and reused in the area, etc.
- Take a field trip to a local water treatment plant to expose students firsthand to the complex process of water treatment and reinforce the need for water conservation.
Check for Understanding
Have each student write an article or editorial discussing his or her ideas about one of the following topics. Let students know that they will need to support their ideas using information they learned from the multimedia resources. You may also want to encourage students to conduct additional research online and/or seek out individuals in the community to interview about local efforts regarding their chosen topic. (Note: You can have students submit their pieces to a school or other newspaper.)
- Importance of conserving water and techniques for reducing water use at home
- Positive and negative effects of dams and techniques that big cities can implement to eliminate the need for dams
The Digital Library for Earth System Education (www.dlese.org) offers access to additional resources on this topic.