Students will investigate water desalination, phase changes, and sustainable freshwater production by designing and building their own solar desalination device. Using a shallow basin, prepared saltwater, collection cup, transparent cover, and solar energy, students explore how evaporation and condensation can separate water from dissolved salt.

During a five-hour investigation, students measure freshwater production, observe condensation and droplet movement, graph cumulative water collection, and evaluate how effectively their solar desalination device performs. Through engineering design, quantitative data collection, graphing, analysis questions, and a structured Claim–Evidence–Reasoning (CER) response, students connect the water cycle and phase changes to real-world water sustainability and engineering.

Learning Targets

• Design and build a functional solar desalination device
• Explain how evaporation and condensation separate water from dissolved salt
• Describe how solar energy drives thermal desalination
• Measure freshwater production over time
• Collect and analyze quantitative data
• Create and interpret a line graph showing cumulative freshwater production
• Evaluate the effectiveness and efficiency of a desalination design
• Use evidence to propose improvements to the system
• Explain the benefits and limitations of desalination

What’s Included

Teacher Guide

Background explanations of desalination, solar stills, evaporation, condensation, salt separation, solar energy, and sustainable water production. Includes safety notes, challenge constraints, implementation guidance, expected results, and common classroom pitfalls with practical fixes.

Student Packet

Driving question, hypothesis prompt, variables chart, engineering design plan, step-by-step device-building instructions, freshwater-production data table, observation prompts, calculations, graphing task, analysis questions, and a guided CER response.

Data Collection & Graphing

Students measure cumulative freshwater collection and water produced during each interval. They create a line graph of Cumulative Freshwater Collected vs Time and analyze patterns in water production and device performance.

Analysis & Answer Key

Sample freshwater-production data, a completed line graph, expected patterns, detailed analysis-question responses, scientific explanations, common sources of error, and a complete model CER connecting solar energy, evaporation, condensation, salt separation, and design efficiency.

Rubric

Assesses understanding of the challenge, hypothesis, engineering design, variables and controls, procedure, data collection, observations, graphing, data analysis, scientific understanding, CER writing, and design improvements.

What Students Will Learn

• What desalination is and why it is used
• How a solar still separates water from dissolved salt
• How solar energy causes water to evaporate
• How water vapor condenses and is collected as freshwater
• Why dissolved salt remains in the source basin
• How to design and test a solar desalination device
• How to measure and graph freshwater production over time
• How to evaluate the efficiency of an engineering design
• How desalination can support water sustainability
• How to use Claim–Evidence–Reasoning (CER) to evaluate an engineering solution

Why Teachers Love It:

• Real-world sustainability connection — students explore a technology used to address freshwater shortages
• Hands-on engineering design — students build and evaluate their own functioning solar still
• Builds core lab skills: variables, measurement, data collection, graphing, and analysis
• Combines physical science, environmental science, Earth science, and engineering
• Includes quantitative data collection, not just a one-time device build
• Makes evaporation, condensation, and salt separation visible and meaningful
• Encourages students to evaluate water production, efficiency, and sustainability trade-offs
• Includes structured CER writing and design improvement
• Perfect for water-cycle units, phase-change units, sustainability units, environmental science, or engineering challenges

➡️ You can get this STEM as well as all my other ones in this series inside my STEM Investigations Growing Bundle. As more labs are added, the price will increase. CLICK HERE to have a look

Best For

Physical Science, Earth Science, Environmental Science, the water cycle, phase changes, desalination, renewable energy, sustainability, engineering design, data collection, graphing, CER writing, STEM challenges, or project-based learning.

Materials Needed

Shallow basin, tray, bowl, or wide recycled container; small collection cup; clear plastic wrap or another transparent cover; rubber bands, tape, or clips; small pebble, washer, or other safe weight; prepared saltwater; graduated cylinder, syringe, or small measuring cup; timer or clock; permanent marker; ruler; student packet (included).

Estimated Timing

Day 1: Design → build → setup → initial measurements

Hours 1–5: Observe condensation → measure collected water → record data and observations

Day 2 or After Collection: Final measurements → graphing → analysis questions → CER writing → design evaluation

Allow approximately 45–60 minutes for designing and building, followed by a 4–6 hour exposure period with brief scheduled measurement intervals. Additional time is needed for graphing, analysis questions, CER writing, and design evaluation.

➡️ You can get this activity inside my STEM Investigations Growing Bundle.

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NGSS Alignment

MS-PS1-4 — Develop a model that predicts and describes changes in particle motion, temperature, and state when thermal energy is added or removed.

MS-ESS2-4 — Develop a model describing how water cycles through Earth’s systems through processes driven by solar energy and gravity.

MS-ETS1-1, MS-ETS1-3 — Define the criteria and constraints of a design problem and analyze test data to determine the effectiveness of engineering solutions.

Assessment

Use the included rubric to score understanding of the challenge, hypothesis, engineering design, variables and controls, procedure, data collection, observations, graphing, data analysis, scientific understanding, CER strength, and design improvements.