Solar Still Challenge

Learning Guide

A simple guide to lead you through the kickoff, the core challenge, and everything in between.

Mai’s Tips

1. Encourage your learner to take notes or draw observations throughout the experiment – especially while waiting for the still to produce water, they can record predictions and thoughts.
2. If you don't have 'dirty' water readily available, simply add a few drops of food coloring and a pinch of soil to clean water to simulate it.

Prep Before Session 15 min

• Gather a large bowl, a small cup, plastic wrap, a small rock, paper, and a pencil.
• Identify a sunny outdoor spot where the solar still can remain undisturbed for several hours.

Photo by Rajesh S Balouria on Pexels

1Introduction 5 min

• Welcome your learner and set the stage. Explain that while there's a lot of water on Earth, much of it isn't safe to drink, leading to "clean water scarcity" – meaning not enough water that's safe for drinking, cooking, and hygiene.

  Ask: "What kinds of situations might make clean water scarce?"

  Ask: "What makes water 'dirty'?

  Ask: "Why can't we just drink ocean water?"

  Encourage them to think about how people might get clean water without a tap, focusing on physical solutions. Guide them to brainstorm initial ideas.

  Done: They've identified a few scenarios for water scarcity and suggested some ways to solve it.

Know Before You Teach

• Good to know: Only about 3% of Earth's water is fresh water, and most of that is locked in glaciers or underground, making readily available clean water scarce for many.
• Ocean water cannot be drunk due to its high salt content, which would dehydrate the body further as kidneys work to expel the excess salt.
• If they ask: So, is 'clean water scarcity' the same as a drought? While drought makes water scarce, clean water scarcity specifically means there isn't enough safe-to-drink water, even if there's water around that isn't purified.
• Key words: Clean water scarcity: A situation where there isn't enough safe water for people to drink, cook, and keep clean.

• It's working when: The learner lists at least two distinct situations (e.g., natural disaster, remote area) or types of 'dirty' (e.g., muddy, salty).
• If they're stuck: Imagine you're camping far away from any town, or a big storm has knocked out water pipes; how would you get clean water then?
• Easier: Provide two example situations of water scarcity and ask them to choose one to discuss.
• Harder: Ask them to consider which populations or regions are most affected by clean water scarcity globally.

Done when: Student identifies a few scenarios where clean water is scarce and offers initial thoughts on solutions.

Photo by MART PRODUCTION on Pexels

2Explore & Plan 8 min

• Shift the focus to nature's way of purifying water, like the water cycle. Introduce the concept of a "solar still" as a device that uses solar energy to purify water by mimicking natural processes.

  Ask: "How does the Earth naturally purify water, like in the water cycle?"

  Brainstorm materials needed to capture sunlight, hold dirty water, and collect clean water separately. Have them use paper and pencil to sketch a basic design plan for their solar still.

  Ask: "What materials do you think we will need?" (Referencing the provided materials list: Large bowl, Small cup, Plastic wrap, Small rock, Dirty water, Paper, Pencil).

  Ask: "What do you expect to happen inside your solar still once it's built and in the sun?"

  Ask: "How will your design ensure the dirty water doesn't mix with the clean?"

  Done: They have a basic design sketch, a prediction (hypothesis) of how it works, and have gathered the materials.

Know Before You Teach

• Good to know: The water cycle involves evaporation (liquid to gas), condensation (gas to liquid), precipitation (falling back as rain/snow), and collection.
• Key components of a solar still include a basin for dirty water, a transparent cover to trap heat and allow condensation, and a collection vessel for purified water.

• If they ask: What's the difference between a 'solar still' and a 'solar panel'? A solar still purifies water using the sun's heat, while a solar panel turns the sun's light into electricity.
• If they ask: What is a hypothesis? A hypothesis is an educated guess about what you think will happen in an experiment, based on what you already know.
• Key words: Solar still: A device that uses energy from the sun to turn dirty water into clean, drinkable water.
• It's working when: The sketch clearly shows a container for dirty water, a separate container for clean water, and a way to cover it.
• If they're stuck: Think about how dew forms on grass or how a mirror fogs up after a hot shower; what are those processes doing with water?
• Easier: Provide a partially completed sketch and ask them to add one missing part.
• Harder: Ask them to include labels on their sketch explaining the function of each part.

Done when: Student has a basic design plan, a hypothesis for how it will work, and has gathered the necessary materials.

Photo by Vanessa Loring on Pexels

3Discussion 6 min

• Review the science behind water purification. Explain Evaporation: when liquid water heats up and changes into an invisible gas called water vapor (like a puddle drying up or water boiling). Its opposite is condensation. The sun provides the energy for this. Explain Condensation: when water vapor cools down and changes back into tiny liquid water droplets (like fogging up a mirror or dew forming on grass). Its opposite is evaporation.

  Ask: "What specifically happens when water changes from a liquid to a gas, and then back again?"

  Ask: "What role does the sun's energy play in making this process happen?"

  Ask: "Where does the 'dirty' stuff go during this process?"

  Emphasize why the clean collection cup must be separate: to ensure only purified water, free of impurities, is collected.

  Done: They can explain evaporation and condensation, and how solar energy powers the purification.

Know Before You Teach

• Good to know: When water evaporates, only the pure water molecules turn into gas, leaving behind any dissolved salts, dirt particles, or germs.
• Condensation occurs when warm, moist air (water vapor) touches a cooler surface, causing the water vapor to lose energy and change back into liquid water droplets.

• The sun's energy provides the heat required to increase the kinetic energy of water molecules, allowing them to escape the liquid phase as gas (evaporation).
• If they ask: Does saltwater evaporate differently than freshwater? No, the water molecules themselves evaporate the same way, but the salt is left behind because it doesn't evaporate at the same temperature as water.
• If they ask: Can you drink the condensed water right away? Yes, once condensed, the water is purified and safe to drink, assuming the collection container is clean.
• It's working when: The learner uses the terms 'evaporation' and 'condensation' correctly when explaining the process.
• If they're stuck: Imagine a kettle boiling; what's that steam, and what happens if it hits a cold window?
• Easier: Focus on just one of the processes, either evaporation or condensation, and ask them to describe it.
• Harder: Ask them to explain why a solar still wouldn't work as well on a cloudy day or at night.

Done when: Student can explain evaporation and condensation, and the role of solar energy in the purification process.

Photo by Engin Akyurt on Pexels

4Activity 9 min

• It's time to build the solar still! Encourage your learner to lead the assembly, offering help only if they get stuck.

  First, place the large bowl in a sunny spot.

  Next, put the small cup in the center of the large bowl. Ensure it's empty and doesn't touch the sides.

  Carefully pour the dirty water into the large bowl around the small cup, being careful not to splash any into the small cup.

  Cover the large bowl tightly with plastic wrap, sealing the edges completely.

  Place the small rock on top of the plastic wrap, directly over the center of the small cup, to create a drip point.

  Finally, leave the assembled solar still undisturbed in the sunny location.

  Done: The solar still is fully assembled and correctly positioned in a sunny spot.

Know Before You Teach

• Good to know: The plastic wrap creates an airtight seal that traps the water vapor inside the still, preventing it from escaping.
• If they ask: How long until we see clean water? It can take several hours, usually a full sunny day, for enough water to evaporate and condense to collect a noticeable amount.
• If they're stuck: If the plastic wrap isn't tight, imagine what might happen to the water vapor; will it stay inside or escape?
• Easier: Verbally guide them through each step as they perform it.
• Harder: Ask them to explain why each step is being performed as they build it, based on their design plan.

Done when: Student has successfully assembled their solar still and placed it in a sunny location.

Photo by Dii Nyau on Pexels

5Summary 2 min

• Praise your learner's efforts and ingenuity. Now, help them reflect on their engineering challenge.

  Ask: "What was the most surprising thing you learned or observed during this challenge?"

  Ask: "What would you change if you did it again to make your solar still more efficient?"

  Ask: "How could this simple solar still be crucial in helping people in remote areas or during natural disasters?"

  Connect their work to real-world applications and careers, like environmental engineering or disaster relief, emphasizing the impact of their problem-solving skills.

  Done: They've shared at least one key takeaway or reflection from the challenge.

Know Before You Teach

• Good to know: Engineering design involves identifying a problem, brainstorming solutions, designing, building, testing, and improving a prototype.
• Careers like environmental engineering involve designing systems and technologies to solve environmental problems, including clean water access.
• If they ask: Is the water collected from a solar still completely pure, like distilled water? Yes, theoretically, the water collected through evaporation and condensation is very pure, similar to distilled water, as impurities are left behind.

• If they ask: What other ways can people purify water in emergencies? Other ways include boiling, using water purification tablets, or specialized filters, but a solar still is unique because it uses sunlight and common materials.
• It's working when: The learner connects their solar still experience to at least one real-world scenario or future improvement.
• If they're stuck: Think about the toughest part of the challenge for you; what did you learn from that?
• Easier: Provide sentence starters for their reflections, such as 'I was surprised by...' or 'Next time, I would change...'
• Harder: Challenge them to research and propose one specific design modification that could increase the still's efficiency.

Done when: Student shares one key takeaway or reflection about the challenge.

Your Notes