Building a Solar Still
- Africa, Cape Verde
- Grades 3-5, Grades 6-8
- Two class periods, 45-60 minutes each
In this lesson, students explore the water cycle and the role it can play in making water drinkable. Through an online video, Peace Corps Volunteers Nicholas Hanson and Brian Newhouse describe how they built a solar still to distill saltwater into drinkable water in Cape Verde. During the first class period, students construct their own model solar stills. In the second class period, they check to see how much pure water their solar stills produced from a supply of saltwater.
- Students will describe how water can change forms through the processes of evaporation and condensation
- Students will explain how a solar still functions to purify water
- Students will discuss how water distillation can benefit human communities
- World map
- Large bowl
- Short glass or cup
- Plastic wrap
- Small rock
- Pitcher of water
- Liquid measuring cup
- Looking at a globe, discuss: What covers most of the earth? Can we drink all of the water that covers earth? Why not? Explain that most bodies of water on earth contain saltwater, and few bodies of water (lakes, rivers) contain freshwater. Less than 1% of water on earth is usable by humans.
- Ask students to brainstorm all the places they can think of on earth where there is water. Prompt students to think about less obvious sources (e.g. not in liquid form). Is the water in these places freshwater or saltwater? [Possible lists: Saltwater—Oceans, seas; Freshwater—Lakes, rivers, glaciers, atmosphere/clouds, inside plants/animals; Both—Groundwater (can be saline or fresh) ]
- Explain that many people get their drinking water from underground. Groundwater is usually pure and good to drink. Near the ocean, however, it can contain too much salt. This can be a problem for people in areas with little access to freshwater.
- Tell students they are going to see how people in Cape Verde are dealing with this problem. Find Cape Verde on a map; provide some information about the culture and geography. Introduce Nicholas Hanson and Brian Newhouse as Peace Corps Volunteers serving in Cape Verde. If students are unfamiliar with Peace Corps, share some background information ( http://www.peacecorps.gov/ ).
View the video Bringing Water from Sol to Soul. Then discuss:
- What problem were Nicholas and Brian trying to solve? [remove salt from the groundwater so it would be drinkable]
- What did they do to solve the problem? [built a solar still to distill the saltwater into freshwater]
- How did the solar still work? [The sun heated up the saltwater, causing the water to evaporate, but leaving the salt behind. The evaporated water condensed on a plastic sheet, and turned back into a liquid form containing no salt]
Now students are ready to practice distilling saltwater into freshwater. To prepare, read the activity instructions then view a short demonstration video. Provide each group of students with the materials (above) and demonstrate how to set up the model solar still. As students build their solar stills, ask them to make predictions such as:
- What do you think will happen?
- Will this solar still be able to turn saltwater into freshwater? If so, how?
- How much freshwater do you think will be produced?
- Where do you think the salt will go?
- How long do you think it will take to distill the water?
- What would make it go faster?
- Ask students to make visual observations of their solar stills. What happened? How accurate were students' predictions?
- Deconstruct the solar stills. Measure the amounts of distilled water collected in the cups. Have students taste the water to see if it still contains any salt.
- Ask students to posit explanations about what happened. How did the water in the cup become purified? Discuss the processes of evaporation and condensation, and their roles in the distillation process.
- Refer back to Nicholas and Brian's project in Cape Verde. How did the ability to distill water impact the people in their community? Why is distillation useful to people with limited access to freshwater?
Frameworks & Standards
- Access to freshwater is essential for human survival
- Freshwater is not equally accessible in all areas of the world
- Knowledge of scientific principles, such as the water cycle, can be beneficial for solving problems
- Why do people need freshwater?
- How does water change states through the water cycle?
- How can scientific knowledge be used to solve real-world problems?
- Content Standard A: Science as Inquiry
- Content Standard B: Physical Science
- Content Standard E: Science and Technology
- Content Standard F: Science in Personal and Social Perspectives
- Essential Element I: The World in Spatial Terms
- Essential Element II: Places and Regions
- Essential Element III: Physical Systems
- Essential Element V: Environment and Society
- Thematic Strand III: People, Places, and Environment
- Thematic Strand VIII: Science, Technology, and Society
- Thematic Strand IX: Global Connections