Experiment

Building a Water Filter

30–90 minIndoor & Outdoor

With sand, gravel and activated charcoal, children build a simple water filter and are amazed as murky water turns clear.

Learning goal

Children understand how natural filtration works and why clean water is a precious resource.

1
Cut the top off the PET bottle and place it upside down in the collecting container.
2
Put a layer of cotton wool or a coffee filter in the bottle neck at the bottom.
3
Add a layer of activated charcoal above it (about 3 cm).
4
Then fill in a layer of fine sand (about 5 cm).
5
Place a layer of coarse gravel on top (about 3 cm).
6
Slowly pour the murky water in at the top and watch the filtered water come out below.
7
Discuss: why is the water clearer now? (Caution: not drinkable!)