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AILEEN SON/The New York Times News Service

Let’s Talk Science and the Royal Society of Canada have partnered to provide Globe and Mail readers with relevant coverage about issues that affect us all – from education to the impact of leading-edge scientific discoveries. Let’s Talk Science offers a number of fun activities to get youth engaged in STEM.

Water is a precious natural resource. What happens if it gets polluted? Learn how water can be cleaned with this hands-on activity?

What You Need

● Plastic funnel - 1

● Gauze pad - 1

● Straws - 4

● Coffee filters - 2

● Small bag of stones

● Small bag of sand

● Small bag of gravel

● Paper towel - 1

● Masking tape

● Paper for blueprint

● Plastic 2 oz. cups - 2

● Craft sticks - 2

● Elastics - 2

● Potting soil (1 cup)

● Water

● Scissors

● Plastic drinking cups – 2

*Safety first!

Soil contains bacteria and other microscopic organisms. Be sure to wash your hands after completing this activity.

The use of scissors should be closely supervised by an adult.

Even if the filtered water looks perfectly clean, do not drink it as it may contain bacteria and other microscopic organisms that may make you sick.

What to Do

  • The challenge: the goal is to filter the dirty water using the materials provided.
  • If you are using stones, gravel and sand collected locally, thoroughly wash and dry these before use.
  • Design, draw and label your filtration system on paper first.
  • Build the system using the materials on hand.
  • Once built, test the system using dirty water made by mixing 2 tablespoons of soil in one cup of water.
  • Does the filtration system get the water clean? What filtration materials made the most difference in the appearance of the water? Is there an order to the filtration materials that works best to clean the water?

What’s happening?

Water filtration is a method of cleaning water by passing it through a filter (permeable substrate). Permeability (perm-e-a-bil-e-tee) is the measure of how easily a liquid can pass through a substance.

This activity explores the various filter media available. Once water is dirty or polluted, it can be very complicated to clean. Many steps may be necessary to filter dirty water! The rocks and sand formed by erosion perform a very important function: they help to clean our water supply. Sand and gravel make good water filters because they form permeable layers. When the sand particles are next to one another, there are tiny spaces between them. Water can pass slowly through these tiny spaces and some of the dirt particles get trapped. The smaller the particles, the smaller the spaces will be in the layer and the smaller the dirt particles that can be trapped.

When comparing the rate of flow between different filters, it is generally found that the tighter the spaces in the filter, the slower the flow of water. These small spaces cause tiny dirt particles to be trapped in the filter media. A slower flow of water through the system produces cleaner water!

Why does it matter?

In the environment, erosion is responsible for the movement and redistribution of sand and gravel, which helps clean our natural water supply. A more complex version of sand and gravel filters are recreated in water treatment plants where it helps remove fine bits of floc, algae and silt from the water. This is only one step of the purification process of drinking water.

Wetlands are also very important in cleaning water. They are very effective at cleaning water and acting as large filters to help decrease the amount of water pollution. Do some research to learn why wetlands are so effective in cleaning water. Discuss why it is important to protect wetland areas.

Investigate further

● How many steps are needed to filter the dirty water? Can you do it in fewer steps?

● Compare the efficiency of large gravel versus small sand granules, which relates to the filtering of water found in nature.

● Compare the rate of flow between different filtration systems.

● Create a filtration system using peat moss (available from gardening centres) or activated charcoal (available in many drug stores). Compare the results.

● Discuss the importance of water and water quality in our daily lives.

● Discuss the filtration process (the use of large stones versus small ones).

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