Rainbow Walking Water Experiment

Why does the water walk up the paper towel to the other side? Sounds like an age-old riddle, but it’s actually science! Learn all about it in this rainbow walking water experiment.

How do you get water from one cup to another without touching the cup? It sounds like a magician’s trick, but it comes to just science.

You only need a few items to set up this rainbow walking water experiment, and you probably already have everything you need in the house.

How to Do the Walking Rainbow Water Experiment

Supplies:

• 6 identical cups or jars (glass or clear plastic so you can see the height of the water)
• Paper towels
• Food coloring

Directions:

1. Fill three cups about 3/4 full with water.

2. Add a few drops of food coloring and stir. We used the primary colors red, blue, and yellow to get the rainbow effect.  

3. Place the empty cups between the cups filled with water.

4. Fold the paper towel lengthwise until it’s about 1 inch wide.

5. Put one end of the paper towel in the cup with the colored water and the other end in the empty glass. Tip: You may want to trim your paper towel if it’s sticking up in the air too much.

6. Leave everything alone and check back occasionally to observe the progress.

Eventually, all the cups will be filled with the same amount of water. At this point, the water will stop moving from one container to another.

How long does it take for the walking water experiment?

Depending on the type of paper towel you use, water may start “walking” up the paper towel within minutes. However, typically it takes 20-30 minutes for the water to travel from one glass to another. It may take another couple of hours for the entire process to complete.

The first time we did this experiment, nothing happened for the first 10 minutes. We ran out to grab dinner, and by the time we returned home an hour later, the water had started moving up the paper towel. We went to sleep that night with no water yet in the empty cup and woke up to the same amount of water in both cups. Pretty cool!

We revisited this walking water experiment and this time, the water traveled up the paper towel much faster. We could see the water going up the veins of the paper towel immediately, and the whole process took less than an hour to complete.

You can try different brands of paper towels if it seems like it’s taking forever. You can also add more water to get things moving.

Why does the water climb the paper towel?

The capillary action is responsible for the water moving up the paper towel. It’s also the process that plants use to pull water up from the ground through their roots!

The capillary action is the process in which a liquid moves upward through a narrow space as a result of cohesion, adhesion, and surface tension. Let’s break down each one of these forces in simple words.

Water is “sticky,” meaning that water molecules like to stick to other water molecules. This attraction is called cohesion.

However, water molecules also like to stick to solid substances, called adhesion. Therefore, when one water molecule attaches to the paper towel, it wants to bring its buddies along for the ride.

Lastly, water molecules are more tightly bound together at the surface, creating surface tension. Therefore, the surface tension pulls the water molecules upwards through the tiny gaps between the cellulose fibers of the paper towel.

Final Thoughts on the Walking Water Experiment

Hope you and your kids liked this amazing science experiment! For more awesome science experiments, check out:

• Colorful Magic Milk Experiment
• Naked Egg Experiment
• Celery and Food Coloring Science Experiment
• Grow a Rainbow on Paper Towel Experiment
• How to Make a Rainbow Water Beads Sensory Bottle