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Capillary Action Science Experiment
How does water climb uphill? The answer will surprise you
MIDDLE CHILDHOOD ACTIVITIES
8/27/20263 min read
Water flows downhill. Everyone knows that. Except - it doesn't always. In the walking water experiment, coloured water travels upward through paper towel against gravity, moves across to an empty cup and drips down the other side.
And the reason it does this - capillary action, the same force that pulls water from the roots of a tree all the way up to its highest leaves - is one of those scientific concepts that genuinely changes the way children aged 7–10 see the natural world. This is the experiment that makes children look at trees differently. That's a pretty remarkable thing for a few cups of water and some paper towel to do.
Why This Activity Works
Capillary action is a real, important scientific concept that children this age are ready to understand and explore properly. The experiment itself is visually spectacular - making it the perfect vehicle for introducing a complex idea. At this age children can move beyond simply watching to genuinely experimenting - varying the paper type, the distance between cups, the concentration of colour - and recording what changes. Connecting capillary action to how plants drink water bridges the experiment to the natural world in a way that is genuinely illuminating.
Activity Details
Age Range: 7 – 10 years
Time: 15 minutes setup + ongoing observation over several hours
Mess Level: Mild - food colouring can stain, protect surfaces! 🌈
Supervision: Nearby supervision
What You'll Need
7 clear cups or glasses
Water
Food colouring in red, yellow and blue
Paper towel strips for the standard experiment
Additional materials for variations — kitchen paper, newspaper, fabric strips, coffee filter paper
A ruler for measuring water travel
A science notebook for recording hypotheses and results
A timer or clock for recording speed of travel
Optional: white carnations or celery stalks for the plant extension experiment
How To Do It
Part 1 — The Standard Experiment:
Set up 7 cups in a row - fill alternating cups with coloured water (red, yellow, blue, red) leaving the cups between empty.
Record the hypothesis - what do you think will happen? How long will it take?
Connect cups with folded paper towel strips.
Record the start time.
Check every 15 minutes and record observations - how far has the water travelled? What colours are forming in the empty cups?
Record the finish time when cups are full and colour mixing is complete.
Part 2 — The Variables Experiment:
Set up identical experiments using different materials - kitchen paper, newspaper, fabric, coffee filter paper.
Record a hypothesis for each - which material do you think will be fastest? Why?
Time how long each takes to transfer water.
Record results and compare - which was fastest? Which produced the most vivid colour?
Part 3 — The Plant Connection:
Place a white carnation or celery stalk in a cup of deeply coloured water.
Leave for several hours or overnight.
Observe - the colour travels up through the stem into the petals or leaves.
Discuss - this is capillary action in a living plant. How does a tree get water to its highest leaves?
Record conclusions - write up the full experiment with a proper scientific conclusion.
Kim's Tips 💕
The white carnation extension is absolutely stunning - watching petals turn pink or blue overnight is genuinely magical and makes the science completely real.
Coffee filter paper transfers colour fastest - a fascinating variable that always surprises children.
Measuring the water level in the receiving cups every 15 minutes and graphing the results introduces basic data recording in the most engaging possible way.
The tree question - how does water get to the top of a tall tree? - is a beautiful discussion to have before revealing the answer. Children's guesses are always wonderfully creative.
This is a perfect activity for grandchildren on a longer visit - set it up together in the morning, check on it throughout the day and discuss the results over dinner.
Looking up capillary action in plants online together after the experiment deepens the learning beautifully - there are some extraordinary time-lapse videos of plants drinking coloured water.
What You'll Need
Clear cup sets, food colouring kits, science notebooks, are all on my Amazon storefront.
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Let's stay connected!
This post is part of my Middle Childhood Activity Hub- packed with ideas for 7-10 year olds.
With love, Kim xx
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