How to Teach About Water Filtration

A water filtration science project is a hands-on way to teach students about how water is cleaned. Using common items to make this water filter, students will be able to watch visibly dirty water get cleaned. Older students can take the used water filter apart to study which filter substrates are most effective against different types of dirt. This water filtration science project is appropriate for grades K-12.

Things You'll Need

• 2-liter soda bottle
• 40 cotton balls
• 1 cup gravel
• 1 cup sand

Instructions

Make a Water Filter

1. Cut a 2-liter soda bottle in half. The top half of the soda bottle will be used to make the water filter. Set the bottom half of the soda bottle aside. It will be used to catch the clean filtered water. Note: An adult should be the one to cut the soda bottle in half.

2. Turn the top half of the soda bottle upside down. The spout of the bottle should be facing down.

3. Stuff 20 cotton balls into the top half of the soda bottle.

4. Slowly pour 1 cup of gravel on top of the cotton balls.

5. Spread 20 more cotton balls on top of the gravel. The gravel should be completely covered by the cotton balls. Use more cotton balls if needed to cover the gravel.

6. Pour 1/2 cup of sand evenly over the cotton balls.

Perform the Experiment

1. Put the soda bottle water filter spout side down inside the bottom half of the soda bottle.

2. Make 1 cup of dirty water by adding one or more of the following ingredients: cooking oil, food coloring, or food particles.

3. Pour the dirty water through the water filter and watch clean water come out into the bottom half of the soda bottle.

4. Take the water filter apart to see which parts of the filter cleaned the different dirty water items.

5. Talk to the students about how the soda bottle water filter is similar to water filtration in streams and filters in home filtration systems. The soda bottle water filter cleans water with gravel and sand similar to how a stream or river does. A home filtration system filter catches dirt and cleans water in a similar way that the soda bottle filter does.

Tips & Warnings

• Allow older students to experiment with different filter substrates and different forms of dirty water.

• Do not allow students to drink the filtered water. Even though it appears clean, it is untested and could contain harmful bacteria.