This fun science experiment turns dirty water clean. (Kind of.)
How do you clean up dirty water?
Not with soap! You need a filter, a device that removes impurities, like dirt, from water. The filter you’ll make here—with the help of an adult—is a super strainer, and it’ll help you clean up your act.
Step 1
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Ask a grown-up to cut the bottle in half. Then flip the bottle's top half over and put it in the bottom, so the top looks like a funnel. You'll build your filter in the top part.
Step 2
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Place the coffee filter (or bandanna, sock, etc.) at the bottom of your filter.
Step 3
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Add cotton balls, charcoal, gravel, sand, and / or other materials in layers. You can use just one of them or all of them. Tip: Think about which order to add them. Bigger filter materials usually catch bigger impurities.
Step 4
Write down which filter materials you used and in what order you layered them.
Step 5
Stir your dirty water and measure out a cup of it.
Step 6
Get your timer ready!
Step 7
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Pour a cup of dirty water into your filter. Start the timer as soon as you begin pouring.
Step 8
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Time how long it takes for all the water to go through the filter. Then write down how long it took.
Step 9
Carefully scoop out the filter materials, one layer at a time. What did each layer take out of the water?
Step 10
Experiment! Clean the bottle and try again. Put the filter materials in a different order each time, and time each experiment. What do you discover?
WHAT'S GOING ON?
The slower, the better! The longer it takes for water to move through a filter, the cleaner it gets. Water slips easily through the filter materials, but bigger gunk, like dirt, gets trapped. The filter materials usually get finer and finer, so they can catch whatever was missed earlier. Activated charcoal can be near the end of the water’s path, because it uses an electrical charge to grab particles too small for us to see.
Your filtered water is not clean enough to drink. But a plant will love it!
Photographs by Mark Thiessen / NG Staff: Adapted from the Nat Geo Kids book How Things Work, by T.J. Resler
