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How to Make a Simple Water Filter

A simple filter can clean muddy water so that it looks clear. However, it cannot make water safe to drink, because it does not remove germs. Use this experiment only to learn about filtration. Always boil filtered water for at least five minutes before drinking it.

You will need: a plastic bottle, a piece of cloth, a handful of small stones, two handfuls of coarse sand, two handfuls of fine sand, crushed charcoal, a cup, and a jar of muddy water.

Step 1: Cut the bottle in half. Turn the top half upside down and place it in the bottom half, so that it looks like a funnel.

Step 2: Put the cloth over the neck of the bottle to stop the materials from falling out.

Step 3: Add the materials in layers. Start with the crushed charcoal at the bottom, then the fine sand, then the coarse sand, and finally the small stones at the top. The finest materials must go at the bottom, because the water should pass through the larger particles first.

Step 4: Rinse the layers with clean water until the water running through is clear. This removes dust from the charcoal and sand.

Step 5: Slowly pour the muddy water onto the stones. Collect the filtered water in the cup. If it is still cloudy, pour it through the filter again.

Note: Do not throw away the used sand and charcoal in a river, because they may contain harmful particles.

A student pours muddy water onto the sand first and the stones last. According to the instructions, what is wrong with the filter?