Muddy Water Filter Challenge

What you need

• Clear cups, at least 2 jars
• Water, about 4 cups
• Clear cups, 1 glass
• Soil, 1 spoonful
• Sand, 1 cup
• Small gravel, 1 cup
• Plastic bottle, 1, plus 1 spare to test two filters
• Coffee filter, 1, or a cotton cloth
• Spoon, 1
• Towel, 1 old towel, or a tray
• Kid scissors, 1 pair, for the grown-up

How to do it

Grown-up prep: A grown-up needs to cut the bottom off a plastic bottle. Set up outside or on a tray, since muddy water splashes. Filtered water still has germs in it, so it is never for drinking.

1. Stir a spoonful of soil into a jar of water.
2. Pour some muddy water into a glass to save for later.
3. Ask a grown-up to cut the bottom off the plastic bottle. A grown-up does this
4. Turn the bottle upside down and rest it in an empty jar.
5. Layer in the coffee filter, then sand, then gravel.
   Ask: What do you think each layer will catch?
6. Slowly pour the muddy water through the layers.
7. Compare the filtered water with your glass of dirty water.
   Ask: What looks different, and what do you think got left behind?
8. Rebuild the filter with the layers in a different order.
9. Show your family the clearest jar, and remember: never drink it!
   Ask: What would you add to make the water even clearer?

Play it again

• Order swap: try a new layer order and guess which one will win.
• Two bottle race: build two filters and pour at the same time to see which is faster.
• Extra muddy: add more soil or a few leaves and see if your filter can still cope.