Rainbow Walking Water Experiment
This classic science experiment shows children how water can "walk" uphill through paper towels, mixing colors along the way to create a beautiful rainbow — perfectly timed for St. Patrick's Day. It takes about 20 minutes to set up and several hours to complete, making it a wonderful morning activity to set up and revisit throughout the day.
The science here is capillary action: water molecules cling to the fibers of the paper towel and climb upward, carrying color with them. When two colors meet in the middle, they blend into a third.
What You'll Need
- 7 clear plastic cups — lined up in a row
- Paper towels — strips folded lengthwise, about 1 inch wide
- Food coloring — red, yellow, blue (primary colors)
- Water — enough to fill cups halfway
- A tray — in case of spills
How to Do It
Step 1: Set up cups. Place 7 cups in a row. Fill cups 1, 3, 5, and 7 with water (skipping every other cup).
Step 2: Add colors. Color the water: cup 1 = red, cup 3 = yellow, cup 5 = blue, cup 7 = red (to complete the rainbow circle).
Step 3: Connect with paper towel bridges. Fold paper towel strips lengthwise into a narrow strip. Place one end in cup 1 and the other in cup 2. Repeat between each cup.
Step 4: Watch and wait. Over the next 30–60 minutes, watch the water climb up the paper towels and drip into the empty cups. Colors mix in the empty cups!
Step 5: Observe the results. Cups 2, 4, and 6 will fill with orange, green, and purple — the secondary colors!
🎓 Skills Your Child Will Develop
Color mixing — Seeing red + yellow = orange happen in real time is unforgettable.
Patience and observation — Checking in on the experiment teaches delayed gratification.
Scientific vocabulary — Words like "absorb," "mix," and "blend" become concrete.
Tips & Variations
- Photograph the experiment every 15 minutes to make a time-lapse record.
- Discuss "where do you think the water is going?" before results appear.
- Try with different materials: coffee filters, napkins, cloth — which absorbs fastest?
- Set up a second experiment to test predictions from the first.
My Two Cents
Set this up first thing in the morning and check it after snack, after lunch, and at the end of the day — you'll see clear progress at each check-in. The moment children notice the empty cups filling with a NEW color (one they didn't put in!) is genuinely magical. It's one of the best demonstrations of color mixing because the mixing happens slowly enough to really observe.
