April 20th, 2018

Praxis: Filtration is just one part of water purification

By Medicine Hat News on March 18, 2017.

This week, I thought we could learn about something that covers two-thirds of the Earth’s surface and makes up about 60 per cent of our bodies. Water. Did you know that although there is water everywhere, most of it is inaccessible or humans are not able to consume it? On March 22 it is World Water Day globally. In our community, we often forget that there are millions of people around the world that do not have clean, safe, drinkable water. I know I take it for granted that I can turn the faucet on and have a drink whenever I wish. In recognition of the day, we are proud to be partnering with SEAWA and the Medicine Hat Public Library. We will have some exciting activities for preschoolers that morning. Science is for everyone, and even those young curious little minds can begin to enjoy the science that surrounds us each and every day! I thought what better way to kick off learning about clean water than a great science activity we can do at home. Let’s get started!

*Remember to ask an adult before doing this experiment.


– empty 500 mL plastic water bottle with a lid

– cotton balls

– sand

– gravel


– two different samples of water (get some dirty, muddy ones so you can see the difference)

– nail

– empty clear glass


1. In this experiment we are going to make one of the simplest filtration devices in order to filter out visible impurities in water.

2. Ask an adult to help you cut the flat end off of the water bottle. It can be a bit tricky and I do not want you to cut yourself.

3. Have the adult poke a hole in the middle of the lid with the nail. You want it to go all of the way through.

4. Hold the bottle from the bottom and place 10 cotton balls in the bottom of the bottle (nearest the cap). Carefully push them down so they are compact and all together.

5. Add about five centimetres of sand into the bottle on top of the cotton balls.

6. Place the gravel on top of the sand and cotton balls. Again, you want it to be at a depth of about five centimetres.

7. Place the water filter you made into the empty clear glass.

8. Slowly pour the water sample you collected into the water filter you made.

9. Observe what happens.

10. Look at the water that came out of the water filter.

11. If you want to sample the water you filtered, I advise that you boil it for five minutes before as this type of filter may not remove all impurities and I do not want you to get sick.


There are many steps to purifying water; aeration, coagulation, sedimentation, filtration, and disinfection. In this experiment you only did one of the five steps to water purification, filtration. Filtration is the process where solid particles are removed from the water. In your instance it may have been leaves, sticks and mud. The different layers of materials you made in your filter trapped and filtered out these impurities.

I advised against drinking any water you filtered as some impurities may not have been filtered out. The water may still contain things such as bacteria and other microscopic organisms that can make you sick. Before it is safe for humans to consume, one last step needs to be completed and it is known as disinfection.

It is absolutely amazing how many steps are involved in making sure water is safe for humans to consume. It is a precious resource for all life on Earth and we need to make sure we are all environmental stewards in ensuring our water supply remains safe and useable.

Patty Rooks is senior scientific consultant at PRAXIS, “Connecting Science To The Community.” Contact Praxis at praxis@praxismh.ca, http://www.praxismh.ca, Tweet or follow us @PraxisMedHat, or friend us on Facebook.

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