Water Cycle In A Bag

What's this Science Bite about?

Make your very own mini water cycle, at home or at school.

What you'll need

A clear sealable bag, sticky tape, Permanent marker pen, Blue food colouring, A glass of water, A window, Some sunshine!

  • A clear grip seal bag
  • Sticky tape
  • Permanent marker pen
  • Blue food colouring
  • A glass of water
  • A window
  • Some sunshine!

How to do the experiment

  1. Design your bag. Try to include the sea, some clouds and the sun.

    Design your bag
  2. Add a few drops of blue food colouring to the water.

    Add a few drops of food colouring
  3. Pour the water into the bag. Be careful to make sure the water does not touch the sides of the bag.

    Pour the water into the bag
  4. Seal the bag securely and tape it to a window. Try to use a window that sees a lot of sun.

    seal the bag
    tape the bag to a window
  5. After approximately 30 minutes you should start to see some water droplets forming on the inside of the bag. Tap them to make it rain inside the bag.

    you should start to see some water droplets forming on the inside of the bag
    Tap the water droplets to make it rain inside the bag

Find out more...

What's happening?

The water in the bag will get heated up by the sun and start to turn from a liquid into a gas. This is called evaporation and is exactly what happens to the water in oceans and lakes.

This gas will then try to escape the bag, but as soon as it touches the side it will cool down and turn back into liquid water. This is called condensation. Seeing little water droplets on the side of the bag will tell you that this process is happening.

Condensation also happens after water evaporates from oceans and lakes. This usually happens high up in the sky, but we know that it’s happening because that is how clouds are made.

When the water droplets in the bag get too big they will start to drip. This is called precipitation and also happens when the water droplets within clouds get too big and fall to the ground. We usually call this rain.

Did you notice…

The water you put in the bag was blue, but the droplets that formed due to condensation were clear.

This happened because only the water evaporated and turned into gas, the food colouring was left behind in the blue mixture.

This is also why rain water is not salty, even though most clouds are formed using evaporated sea water.

Curriculum Links

Processes of the Planet

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Glasgow Science Centre