Create a Walking Water Rainbow!

Project Overview: Want to witness water seemingly walk on its own from cup to cup, mixing colors together to create a rainbow — with no pumps, no batteries, and no one touching the cups after it starts? This project uses nothing but paper towels and water to explore a hidden skill that plants use everyday! WARNING: Food coloring can stain clothing and countertops, so work on a covered surface and wear old clothes!

Materials:

1. 7 Clear Plastic Cups

2. Paper Towels

3. Water

4. Red, Yellow, and Blue Food Coloring

5. Scissors

Instructions:

1. Line your 7 cups in a row

2. Fill cups 1, 3, 5, and 7 about 3/4 full with water, and leave cups 2, 4, and 6 empty

3. Add red food coloring to cup 1, yellow food coloring to cup 3, and blue food coloring to cup 5 

4. Stir each one so the color is mixed in well; Cup 7 will stay clear

5. Fold a paper towel lengthwise into a long strip, then fold it in half. Repeat until you have 6 folded strips total

6. Place one end of a strip into cup 1 and the other end into cup 2. Repeat this pattern, connecting every pair of neighboring cups all the way down the row, so each cup is linked to the next by a paper towel strip

7. Step back and check on your cups every 15 minutes over the next 1-2 hours

8. Watch as the water level in the full cups slowly drops while the empty cups begin to fill, and notice the new colors that appear where two colors overlap

Explanation:
Paper towels are made of tiny fibers with narrow gaps between them, and water gets pulled into those gaps almost like it's climbing a tiny ladder — even against gravity. Scientists call this capillary action, and it's actually the same process plants rely on to move water from their roots up to their leaves. Once the water climbs to the top of the strip, gravity takes back over, and it drips down the other side into the next cup, food coloring and all. So when red water comes in from one direction and yellow comes in from another, meeting in the same cup, they mix into a brand new color — and that's the trick behind getting a whole rainbow out of just three colors to start.