Rainbow Walking Water: Color-Mixing Experiment
Rainbow walking water is a capillary action experiment where primary-colored water travels across paper towel bridges and mixes into secondary colors.
Set out cups of red, yellow, and blue water, link them with paper towel bridges, and watch the colors walk into the empty cups. Orange, green, and purple appear as the primaries meet. Movement starts in minutes, and the full rainbow takes 1 to 2 hours.
Key takeaway: Rainbow walking water adds color theory to capillary action: primary colors walk across paper towel bridges and mix into secondary colors in the empty cups. Give it 1-2 hours for the full rainbow.
We set this one up on winter mornings in Ohio and check it between other activities. The rainbow is usually done by lunch.
Why This Project Matters
At Tierney Family Farms, we believe that the best classroom is often the kitchen table or the backyard. For kindergarten kids (ages 5-6), learning isn't just about memorizing facts; it's about touching, seeing, and questioning the world around them. This Rainbow Walking Water experiment develops fine motor skills through pouring and folding, while predicting color mixes introduces the basics of the scientific method.
Classic vs. Rainbow: Pick Your Setup
| Setup | What you learn | Time | Link |
|---|---|---|---|
| Classic 7-cup | Capillary action basics | 10 min setup, 1-2 hours | Walking Water: Capillary Action in 10 Minutes |
| Rainbow (this post) | Capillary action plus color mixing | 30 min setup, about 2 hours | You are here |
Materials You'll Need
Before you start, gather your supplies. Most of these are likely already in your pantry or craft closet.
| Item | Quantity | Notes |
|---|---|---|
| Clear Plastic Cups or Glasses | 6 or 7 | Must be the same size. |
| Water | 3-4 Cups | Room temperature is fine. |
| Food Coloring | Red, Yellow, Blue | Use primary colors for the best results. |
| Paper Towels | 6 or 7 sheets | Plain white paper towels work best. Skip the thick quilted kind, which wicks more slowly. |
| Stirring Spoon | 1 | [Adult Help Recommended] |
| Tray or Cookie Sheet | 1 | To catch any accidental spills. |
Stain warning: food coloring stains skin, clothes, and counters. Cover the table, use old shirts or smocks, and have an adult handle the dye bottles.
Step-by-Step Instructions
Step 1: Line Up Your Cups
Place your 6 or 7 clear cups in a straight line or a circle on your tray. If you want to make a full circle rainbow, 7 cups work best because the last cup can loop back to the first.
Step 2: Fill Every Other Cup
Fill cups 1, 3, 5, and 7 three-quarters full with water. Leave cups 2, 4, and 6 empty. It is important that the water level is high so the walk doesn't take too long.
Ask your child: "Which cups have water and which ones are empty? What do you think will happen to the empty ones?"
Step 3: Add Your Primary Colors
This is the part where the magic starts. [Adult Help Recommended] to keep the food coloring on the cups and not the carpet!
- Add 5-6 drops of Red to cup 1 and cup 7.
- Add 5-6 drops of Yellow to cup 3.
- Add 5-6 drops of Blue to cup 5.
Ask your child: "What are these three colors called? (Primary colors!) What colors do you think they will make when they mix?"
Step 4: Prep the Paper Towel Bridges
Take a half-sheet of paper towel and fold it in half lengthwise, then in half again, until you have a long, thin strip. Trim the ends if they are too long; you want the towel to reach the bottom of the cups without sticking up too high in the air.
Step 5: Create the Bridges
Place one end of a folded paper towel into cup 1 and the other end into cup 2. Then, place a new strip from cup 2 to cup 3. Continue this until all cups are connected by a paper towel bridge.
Step 6: The Waiting Game
Now, we watch! Within just a few minutes, you will see the colored water starting to climb up the paper towels. While the setup takes under 30 minutes, the full walking process can take a couple of hours to complete.
Ask your child: "Look closely at the paper towel. Is the water moving up or down? How can water move up against gravity?"
Step 7: Observe the New Colors
After about two hours, check back. The empty cups should now have water in them! The red and yellow have mixed to make orange. The yellow and blue have mixed to make green. The blue and red have mixed to make purple.
Color-Mixing Chart
| Mix these | You get |
|---|---|
| Red + Yellow | Orange |
| Yellow + Blue | Green |
| Blue + Red | Purple |
The Science Behind the Magic: Capillary Action
So, how does the water "walk"? This experiment is a clear demonstration of capillary action.
Paper towels are made from cellulose fibers (which come from plants!). These fibers have tiny gaps between them. Water is "sticky"; it likes to stick to itself (cohesion) and to other surfaces (adhesion). Because of these forces, the water travels through the tiny gaps in the paper towel fibers. It literally pulls itself along, even moving upward against the pull of gravity!
This is actually how plants and trees survive. Out here on the farm, the trees use capillary action to pull water from the deep soil up through their roots and all the way to the highest leaves. When your kindergarten kids see the water walking, they are seeing the same process that helps our crops grow!
Track Your Results
Turn this experiment into a tracking activity by having your kids document what they observe. Grab a notebook and create a simple chart:
| Time | Glass 2 | Glass 4 | Glass 6 |
|---|---|---|---|
| Start | Empty | ||
| 5 min | |||
| 10 min | |||
| 15 min | |||
| 20 min | |||
| 30 min |
Every few minutes, check the empty glasses. How high is the water? What color is it? Is it getting darker or lighter? Writing it down keeps kids engaged and teaches them how to observe and record data, basic skills for any budding scientist.
You can also draw a sketch of the setup and color it in as the water moves. Visual learners love this part.
Variables to Try
If your little scientist wants to keep going, try these twists:
Paper-towel brand race: Use two different brands of paper towels to see which one walks the water faster. This is a great way to talk about absorbency.
Warm vs. cold water: Set up two rows, one with warm water and one with cold. Check which one moves faster.
Time-lapse video: Set up a tablet or phone to take a time-lapse video over two hours. Watching the rainbow form in seconds is incredibly satisfying!
Try the quick version: Walking Water: Capillary Action in 10 Minutes
Frequently Asked Questions
Why isn't the water moving?
The water level is usually too low. Fill cups at least 3/4 full. Check that each towel touches the water and isn't folded too thick.
How long until the colors mix?
Movement starts in about 5 minutes. Full color mixing in the empty cups takes 1-2 hours.
What's the best paper towel?
Plain white, not the thick quilted kind. Thinner towels have smaller fiber gaps that wick water faster.
Can I reuse the cups?
Yes. Use plastic cups with young kids. They're washable and won't break if dropped.
Is this safe for a 5-year-old?
Yes. The only real risk is food coloring stains, so use smocks and supervise the pouring.
Whether you're looking for a rainy day activity or more screen free summer ideas, the walking water experiment is a colorful way to bring farm-style curiosity into your home. Be safe and have fun!