Global Water Availability

This activity is designed for students to practice questioning and critical thinking skills. Students will learn the concept of potable water, i.e. fit or not fit for human consumption. They will also learn that water is not always accessible for use, such as water that is in glaciers or deep underground. Vocabulary words include potable, consumption, freshwater, salt water.

This interactive lecture is appropriate for the intermediate classroom. Instruction time approximately 30 minutes. Assessment time 30-40 minutes. Previous learning should include the water cycle and discussion of prevalence of Earth's water. Prior math topics covered would be percents and fractions.

Materials:

globe
chart paper and marker
squares of 10 x 10 graph paper cut for each student plus a model for the teacher (larger squares if possible) scissors for each student
number line from 1-100

For assessment:

Disk pattern that accompanies the A Drop in the Bucket Project WET activity (found on page 240 of the 2005 edition)
colored pencils
lined paper

Opening: Today, we are going to learn the answer to a riddle. Here it is:

There's a saying that goes: Water, water everywhere, but not a drop to drink. (This could be written on the chart paper and revealed for the students to read). Where could you be for that saying to be true? Jot down student responses on chart paper. Bring out the globe and remind students that 3/4 of the earth is covered with water. So, if the earth is 3/4 water, why do we hear that we need to be careful with our water supply? Doesn't it seem like there's an awful lot of water? If students don't suggest oceans or poles, point to the ocean and ask - Can we drink the water here? No, be sure to explain that the ocean is salt water, which humans can't use as drinking water. Point to the North and South poles and ask - Can we drink the water that's here? No, it's frozen and too far away even if it is frozen freshwater. So - what water do we use? Where would we find it? Have students turn to a partner and discuss. Eventually ask students for suggestions and write them on the chart paper under the heading: Potable (drinkable) Water (Explain the meaning of potable.)

Introduce the term freshwater and compare to salt water. Discuss where freshwater is found. Develop a list of places where freshwater can be found. Next ask students to talk to their partner and estimate how much of the earth's water is fit for human consumption, meaning it is freshwater. Students will put their estimates on the number line using sticky notes. Discuss estimates being in terms of percentage. At this point, the students will need to have their 10 x 10 graph paper and scissors.

Now you will introduce the Facts of Water. Students, the paper you are holding represents all of the water on earth, or 100% of all water on earth. How many squares do you have? (100) But, of all water on earth, 97% is too salty for human consumption. This is the water found in the oceans and seas, and a very few lakes and rivers. How many of the squares do you need to cut off? (97) Teacher models with their 10x10 graph paper. You now have 3 squares left. This represents freshwater, water that is not salty, water that people could use, - except about 80% is frozen at the poles. Is that a problem? (yes, you will refer to previous discussion). Discuss how you would estimate 80% of the remaining squares and show how you would trim 80% off. Discuss how little of the original 100% of water is left. And then - more bad news! Of this amount, 99.5% is polluted, too far underground, or trapped in the soil. Trim off a sliver of your model to show what .5% would be like. Students will follow suit.

Return to original riddle: Water, water everywhere, but not a drop to drink. Ask students how this fits in with today's lesson. Students should be able to respond that there is a lot of water on earth, but most of it is not fit for human consumption for several reasons.

1. Most water is salt water
2. Much water is frozen
3. Much of what is left is polluted, too far underground, or trapped in soil.

Ask students to study their original usable water estimate on the number line and adjust as needed.

This lesson has been adapted from a Project WET lesson, A Drop in the Bucket. Project Wet, Project WET International Foundation, Bozeman, MT, http://www.projectwet.org

Teaching Notes
Only you will know how much support your students will need in the area of percentages. I teach a considerable number of ELL students and know that forms of the same word — consumption, consumable, consume, will need to be explained and reinforced via word wall or science journal words. Also, some students may not realize that the ocean is salty, VERY salty. The concept of underground water, glaciers, pollution, may also need to be introduced prior to this lesson.
The Project WET lesson, A Drop in the Bucket, could also be done as an additional demonstration. The same concept of scarcity of potable water is explored, but may connect with students with different learning styles.

Assessment will be ongoing during the lesson. There is a disk pattern included in the Project WET guide from the A Drop in the Bucket lesson. You will need to make copies for each student. They will color and label the appropriate sections of the pie graph showing the distribution of water sources. You will need to discuss the last .5% that is potable water, and decide how to show that on the disk as it is not sectioned off on the pattern. Students will be given lined paper and asked to respond to the question: Why isn't all the water on earth fit for human consumption?

Standards
Grade 4 Earth and Space
B) Water Cycle, Weather, Climate
2-The student will identify where water exists on Earth