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Usable Water on Earth



TIME REQUIRED: About 30 minutes.

SCIENCE INFORMATION: Even though most of the Earth's surface is water, only 1% of it is fresh usable water. Ninety-seven percent of the Earth's water is saltwater, which contains too many minerals for humans to use untreated. Two percent of our water is "locked up" in ice caps and glaciers, leaving only one percent as usable fresh water.

PURPOSE: To provide the students with an understanding there is a very limited amount of usable water on Earth (water quantity).

OBJECTIVES: The learner will be able to:
1. Identify the percent of salt water, fresh water, and fresh usable water on Earth from a model.
2. Infer there is a very limited amount of usable water on Earth.
3. Model the percent of salt water, fresh water, and fresh, usable water on Earth.

PROCESS SKILLS: Numbering, predicting, forming models.

TEACHER PREPARATION:


What to Use:
1 globe of the Earth
100 pennies for each cooperative learning group (suggest 4 students per group)

Divide class into cooperative groups. The number in each cooperative group is your decision as a teacher. However, three or four students per group seems to work well.

INSTRUCTIONAL STRATEGIES:
Engage: Display a globe of the Earth in front of the class. Rotate it slowly as the class observes. Think about the land space and the water space. Ask the questions: How much of the Earth's surface is water? Approximately 75% of the Earth's surface is water. How much of the total water on Earth is fresh, usable water? Only 1% of it is fresh usable water.

Explore: Each group gets 100 pennies, representing all the water on Earth. Considering all the water on Earth, how many pennies would represent the fresh, usable water?  Each group must come to a consensus and report the number to the class.

Explain: Each group will report their number to the class as a recorder lists the amounts on the board. Discuss the findings and lead the students to the fact that one penny of the one hundred represents all the fresh water on Earth.

VOCABULARY:
    salt water    fresh, usable water
    ice caps       glacier

WHAT DID YOU LEARN?

    1. How may pennies represent salt water?

     Ninety-seven pennies (or 97%) represent salt water.

    2. How many pennies represent all the fresh water in the world?

     Three pennies (or 3%) represent all the fresh water.

    3. How many pennies represent ice caps and glaciers?

     Two pennies (or 2%) represent the ice caps and glaciers.

    4. How many pennies represent all of the rest of the fresh, usable water on Earth?

     One penny (or 1%) represents all the fresh, usable water on Earth.

    5. What is the total number of pennies you have and what do the pennies represent?

     The total number of pennies is 100 (or 100%). The pennies represent 100% of the water on planet Earth.

APPLIED LEARNING:

    1. If one penny represents all the fresh water on the Earth, what would be the quantity for Colorado?

    Colorado, being only a small percent of the Earth, would have only a small percent of the Earth's fresh water.

    2. What is the purpose of taking care of the water we have?

    There is a very limited amount of usable water on Earth, and it is important to maintain water quality through wise use and good water conservation practices.

EXTENSION:

As a student-assisted demonstration, have a student measure 1000 ml of clean tap water into the transparent containers. Encourage the students to suggest what this water quantity might indicate (all the water on the Earth's surface).

Encourage another student to pour 970 ml of the water into another clear container. Have students suggest what this amount of water indicates (all the salt water on the Earth's surface).

Have the students suggest what should be added to the 970 ml of water to make the model more real(salt). Have the students suggest what should happen to the remaining 30 ml of water.

 A logical suggestion would be to pour 20 ml of water into a clear plastic container and freeze the water. The remaining 10 ml of water indicates usable water.

You may wish to pour 5 ml of water into a small clear plastic vial and pollute the water with soil, chalk dust, oil, alcohol and other classroom materials. Encourage the students to recognize the polluted water and discuss the importance of keeping usable water clean.



COLORADO RIVER WATER CONSERVATION DISTRICT
P.O. Box 1120 - Glenwood Springs, CO 81602 - 201 Centennial, Suite 200 - Glenwood Springs, CO 81601
(970) 945-8522 FAX (970) 945-8799
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