Understanding Clean Water: Make a Filtration System

What You Need:

  • Two clear plastic bottles (1.5–2 liters depending on how much material you have)
  • Two tall glasses (or a jar) to collect the filtered water 
  • Scissors or a knife (adult supervision required)
  • Cotton balls or coffee filters
  • Sand
  • Activated charcoal
  • Gravel
  • Rocks
  • Dirty water from a river/pond nearby (or use tap water, and add pollutants such as dirt, kitchen oil, detergent, dust, etc.)
  • A copy of a Venn Diagram

What You Do:

Make the water filtration systems
  1. Explain to your child that they will make two different water filtration systems using the same materials. The only difference will be the order of the materials that are placed in the bottle. (Your child will design the order.)
  2. Help your child cut off the bottom third of the empty bottles. Poke a hole in the bottle caps using a sharp knife. Widen the hole with the scissors. It should be about a quarter inch in diameter.
  3. Tell your child to place a cotton ball or a cutout piece of coffee filter inside the bottle caps. Then, screw the caps back on. Place the cutoff water bottle upside down into the tall glass or jar, making sure there is enough space to hold the filtered water.
  4. Show your child the four materials that will be used in the filtration process. Ask your child to consider which order they think the layers of materials should be and why. Have them design two different systems of layers and explain their reasoning for each design. Create each system using the two bottles.
  5. Here is the standard order of filtration materials, for your reference: Add a layer of charcoal to the upside down water bottle (with the cap down). Each layer should be 1–2 inches thick. Ask your child what they think the charcoal does to the water. Then, build another layer of sand. Continue to discuss with your child the purpose of each of the materials in the filtration system. Finally, add the layer of gravel followed by the layer of rocks.

Water Filtration System

Material Purpose
Activated charcoal Absorbs any unwanted chemicals in the water
Sand Removes fine (tiny) impurities
Gravel Filters out smaller piece of impurities, such as dirt
Rocks Filters out large pieces of impurities, like leaves or insects

Test the filtration systems
  1. Collect some dirty water or make your own.
  2. Have your child make a hypothesis about which filter will work best and why. Also have them predict what the filter will do to the dirty water and what the water will look like once it has gone through the filtration systems.
  3. Place the filters with the cap down into the tall glasses or jars you have. Ask your child to carefully pour the dirty water into each filter. Enjoy watching the water go through each layer of filtration.
  4. Compare the appearance of the filtered water used in each system. Note: Don’t drink the water!
  5. Have your child complete the Venn Diagram by drawing both filtration systems on the diagram and comparing and contrasting the results.


Ask the following questions to spark your child’s interest in the topic of clean water and sanitation:

  1. Have you ever gotten sick from drinking unclean water? Do you know someone who has? What was the experience like?
  2. Do you think everyone should  have access to clean water? Why or why not?
  3. In communities that don’t have access to clean water, what are some solutions that you can think of to solve this problem?

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