Water, Water Everywhere and Not a Drop to Drink!

Goals:

To describe limitations of fresh water resources on ships at sea.

To understand the value of fresh water on the ocean and around the world.

To gain an understanding of the process and economic cost of desalinization.

Content Areas:

Science - desalinization, salt vs. fresh water

Social Studies - fresh water usage

Math - problem solving

Materials:

Three 1 liter flasks or beakers

Graduated cylinder

Water

Procedure: (1 hour)

1) Students should form groups of 3-4 students.

2) The teacher should fill a one liter beaker or flask with tap water and display it to the class. Next, explain to the class that this amount of water represents the world's supply of water. Ask the students to make an educated guess on how much water in the flask represents salt water and how much represents fresh water. Students should also be asked the following questions: Where does the ice for polar ice caps come from? Is this fresh or salt water? What portion of the fresh water would represent the ice caps and glaciers?

3) The teacher should write down the guesses from each group on the board. The teacher should measure 2 ml of water from the flask using a graduated cylinder and transfer the water to a separate 1 liter flask. Transfer 1 mL of water from the original flask into a separate 1 liter flask. These two amounts of water represent the fresh water tied up in the polar ice caps and the remaining fresh water respectively. The amount of fresh water not locked up in ice caps is literally a drop in the bucket.

4) The teacher should explain the difference between salt water and fresh water. Why can't humans drink salt water? Include discussion of major salts such as sodium and magnesium chloride. Can students think of any way to convert salt water into fresh water? Is rain fresh or salt water? How could a sailing ship acquire fresh water?

5) Introduce the concept of desalinization. Explain that through the process of distillation fresh water can be produced from salt water. Also, explain the concept of reverse osmosis, which involves filtering water for salts using thin mineral collecting membranes. Ask students to discuss the cost of these processes.

6) Explain that conventional methods of acquiring water, such as wells and reservoirs, cost about $0.30 per 3800 liters, while water from desalinization plants costs about $1.00 per 3800 liters. Water in grocery stores costs about $0.75 per gallon.

7) Student groups should answer the following questions:
 

In what locations of the world do you think desalinization plants are being built?

What is the source of the water you use for daily cooking, cleaning, and drinking?

How much water do you use daily? Your family?

If a ship crew has 35 members and each member uses 25 gallons of water daily, how much would it cost to supply water to the ship for a 30 day journey using water bottled from a well at their port? From a grocery store? From desalinization aboard the ship? What are the advantages and disadvantages of using each source of water?

Assessment:

Students will be assessed based upon participation in discussion and completion of the problems assigned (see Discussion Rubric). Criteria for success: Although students are working in groups to solve the problems, each must hand in answers to the questions. Students should show their work. A list of the questions asked in Procedures should be handed out to students to answer. Each question is worth 5 points.

Extensions:

Water awareness: Students should keep a log of their personal water use. The log should include their personal use of water, how much they used, and how they could reduce the amount they used. The log could be kept for a day or a week.

 This page was submitted by St. Norbert College Ocean Voyagers Program