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Water Cycle in a Bag

Water Cycle in a Bag

December 21, 2021

Have you ever wondered how water gets from a lake or ocean back into the sky to fall as rain? That is the work of Earth’s marvelous water cycle! The water cycle ensures that water stays in a constant loop between Earth’s surface and the sky, where it forms clouds and eventually falls as precipitation.

- Re-Sealable Plastic Bag
- Permanent Marker
- Water

- Tape
- Blue Food Coloring (optional)

1. Use your permanent marker to draw a sky with clouds and a sun towards the top of your bag.
2. Add some water so that it forms a body of water at the bottom of your bag. Add food coloring now, if using.
3. Seal your bag and hang or place it on or near a sunny window.
4. Wait a few hours to a day (depending on how sunny it is) and see if you notice any changes to your bag.

How does water get from a lake to the sky? Water gets from Earth’s surface to the sky by a process called evaporation. Evaporation is when liquid water heats up and turns into a gas, which enters the atmosphere. That water vapor rises to the cooler sky and forms clouds through a process called condensation, where the water vapor turns back into a liquid. When the clouds get too full of liquid water, it falls back to Earth’s surface as precipitation, starting the process over again!

As the water in your bag is heated by the sun, it begins to evaporate. Since it’s contained by the bag, no clouds can form. Instead, the water vapor condenses and forms water droplets on the inside of the bag. Over time, those water droplets will slide back into the water at the bottom of the bag, starting the cycle over again!