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The walking water experiment

Plants draw water from their roots to their leaves through a process called capillary action. We can see how it works with a paper towel.

Paper towels are fibrous and water can travel through gaps in the fibre to spread through the towel.

If we place a paper towel in a cup of water it will even climb up the towel, going against gravity, as it’s drawn through the gaps in the fibres. Let’s watch some water take a walk!

What you’ll need:

Celery, cups, food dye and paper towelling.
Celery, cups, food dye and paper towelling.

  • 7 plastic cups
  • Paper towel
  • Food colouring
  • Pieces of celery


  • Set out your cups in a row. Pour some water into the first and then every second cup (the 3rd, 5th and 7th) . Leave the 2nd, 4th and, 6th cups empty.
  • Take a sheet of paper towel and fold in half lengthwise, then in half again. You might like to trim length so it can go from one cup to another without too much left over.
  • Put one end of towel into the first cup and then make a bridge over into the second cup. Join up all your cups with paper towel bridges.

Next ...

  • Add a few drops of red food colouring to the 1st and 7th cups
  • Add yellow food colouring, to the 3rd cup
  • Add Blue food colouring to the 5th.

Water travelling via paper towel from one cup to another.
Water travelling via paper towel from one cup to another.


You can see how easily water, and anything dissolved in it, can move through capillary action. Leave it for a while and it will walk into your empty cups!

Let’s take this one step further and watch how it is drawn up through capillary action into leaves.

Simply place a piece of celery stalk with leaves into plastic cups with food colouring. Place them on a window sill where there's light and watch over a few days as the leaves change colour!

Healthy water = healthy plants!