Build your own natural filtration system to see how different layers of materials clean dirty water. You will learn how the earth filters water as it seeps through the ground!

Tools

• scissors

Materials

• plastic water bottle (2 liter, 1)
• cotton balls (5-10)
• activated charcoal or crushed charcoal (1/2 cup)
• fine sand (1 cup)
• small pebbles or gravel (1 cup)
• dirty water (2 cups, mixed with soil/dirt)
• rubber band (1)
• clear glass or jar (1)

Safety

• Adult supervision required when cutting the plastic bottle.
• Do not drink the filtered water; it is for experimental purposes only and may still contain bacteria.
• Wash hands thoroughly after handling dirty water and charcoal.
• Adult supervision required for sharp objects.
• Rubber bands can snap. Wear eye protection if launching projectiles.
• Adult supervision required for children under 8.

Steps

1. Ask an adult to help you cut the plastic water bottle in half horizontally.
2. Take the top half of the bottle (the part with the cap) and remove the cap.
3. Place the top half of the bottle upside down (neck facing down) into the bottom half of the bottle to create a holder.
4. Stuff 5-10 cotton balls tightly into the neck of the bottle to create the first layer.
5. Pour 1/2 cup of activated charcoal over the cotton balls.
6. Carefully pour 1 cup of fine sand on top of the charcoal layer.
7. Add 1 cup of small pebbles or gravel as the final top layer.
8. Place the bottom half of the bottle (which is acting as the base) inside a clear glass or jar for extra stability.
9. Slowly pour 2 cups of dirty water into the top of the filter.
10. Wait for the water to seep through the layers and observe how the water looks when it drips into the bottom container.