Students will model the water cycle in a closed system by creating a mini “water cycle” using a sealed clear bag. By adding energy from sunlight or a lamp, students observe evaporation, condensation, and water movement over time. Through structured observations, optional temperature tracking, and a Claim–Evidence–Reasoning (CER) explanation, students explain how energy transfer drives phase changes and cycling of water—mirroring processes that occur in Earth’s atmosphere.

Learning Targets

• Develop a CER explaining how energy drives phase changes in water
• Observe and describe evaporation and condensation in a closed system
• Connect particle motion and energy transfer to changes in state
• Use qualitative and quantitative observations as scientific evidence
• Identify strengths and limitations of a model compared to Earth’s water cycle

What’s Included

• Teacher Guide: Setup instructions, pacing suggestions for multi-day observations, safety notes for heat and sunlight, and background on phase changes, particle motion, and energy transfer. Includes tips for consistent water volume, placement, and observation intervals to support strong evidence collection.
• Student Packet: Investigation question, step-by-step setup, observation/data table, and a fully scaffolded CER framework prompting students to connect energy input to evaporation, condensation, and water movement in a closed system.
• Observation and CER Pages: Qualitative observation prompts, optional temperature recording table, and structured Claim, Evidence, and Reasoning sections that explicitly require particle motion, energy transfer, and phase change vocabulary.

Why Teachers Love It:

• Extremely low-prep with everyday materials
• Strong visual model of evaporation and condensation
• Excellent support for CER writing and scientific explanation
• Works well as a demo, lab station, or individual investigation
• Easy to differentiate by adding temperature data or extensions
• Ideal bridge between physical science and Earth science concepts

Best For

Earth Science, Water Cycle units, evaporation & phase change, environmental science, data analysis over time, graphing practice, and CER writing.

Materials Needed

Clear zip bag, water (measured), marker, tape, light source or sunny window, student lab sheet (included). Optional: thermometer.

Estimated Timing:

• 45 minutes for setup and initial observations
• 24–48 hours for continued observations
• 20–30 minutes for CER writing and discussion

NGSS alignment

MS-ESS2-4, HS-ESS2-4

Practices: Planning & Carrying Out Investigations; Analyzing & Interpreting Data; Using Mathematics & Computational Thinking; Constructing Explanations; Argument from Evidence