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The Water Cycle

The Water Cycle

January 23, 2020

How does water move from the ground and into the sky, then back to the ground again? Find out in this fun and easy experiment!

Items Needed:

  • Paper Cup
  • Plastic Zip top bag (Needs to be large enough to fit the paper cup)
  • Tape
  • Water
  • Sunny window


  1. Fill the cup about a quarter full with water.
  2. Place the cup inside the plastic bag and zip it closed.
  3. Tape the bag with the cup on the inside to a window where a lot of sun enters.
  4. Check on the cup throughout the day and see what happens. You should start to see water in the bottom of the bag.

What Happened:

The sun heats up the water inside the cup and that water evaporates into a gas called water vapor. Water vapor isn’t visible, but the cycle of what happens next is visible. The water vapor rises and little drops of water begin to form along the inside of the bag in a process called condensation. These water droplets collect, and when they become heavy enough, they pull each other down the sides of the bag. In weather, this step would be the precipitation. If you observe the bag long enough, what do you think will happen? Where will the water from the cup go?

This is how clouds form and make rain. Water evaporates as it’s heated by the sun and the water vapor rises into the air where the water cools and condenses, gathers and creates clouds. When the droplets gather and get heavy, they fall as rain – or in the case of cold weather – snow or sleet!

Experiment Credit:

Image Credit: