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Try this at home Part 2: Cleaning water

Though the center is temporarily closed, we are still passionate about sharing science and space! In this series, get hands-on with some fun and educational activities to do at home with the kiddos.

Cleaning water

NOTE: The water you clean in this activity is not disinfected. Do not drink.


The astronauts onboard the International Space Station (ISS) join those of us on Earth in the recycling effort. The astronauts recycle their water. This includes the moisture they exhale and sweat, as well as the water they use to shower and shave. These wastewaters are purified and then used as drinking water.

The ISS uses filtration and temperature sterilization to ensure the water is safe to drink. Water is checked often to ensure it meets the water quality requirements and monitored closely for bacteria and pollutants.

Click here to download a NASA educator guide for a more rigorous water filtration activity.


  • 2 liters of dirty water (add 1 cup of dirt to 2 liters water to make thin but opaque liquid)
  • 2-liter soda bottle cut in half (by an adult)
  • Alum (found in spice aisle in grocery store)
  • beach sand or play sand
  • coarse sand napkins or paper towels
  • small pebbles (natural colored aquarium rocks work well)
  • cotton balls, coffee filters, old clean socks, tulle and/or gauze squares


  1. Put the top half of the soda bottle upside-down (like a funnel) inside the bottom half. The top half will be where you build your filter; the bottom half will hold the filtered water.
  2. Layer the filter materials inside the top half of the bottle. Think about what each material might remove from the dirty water and in what order you should layer the materials.
  3. Pour the dirty water through the filter. What does the filtered water look like?
  4. Take the filter apart and look at the different layers. Can you tell what each material removed from the water?
  5. Wipe the bottle clean and try again.
  6. Try putting materials in different layers or using different amounts of materials.

NOTE: The water you clean in this activity is not disinfected. Do not drink.


  • Think of a question you want answered. For example, are there better materials for cleaning water?
  • Predict what you think is going to happen. Then, test your hypothesis using different materials.
  • For an added challenge, try using only two or three of the materials to build your filter.

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