Education

Sand filter

You will need:

• a two litre lemonade bottle
• cotton wool
• clean washed sand
• scissors
• sample of muddy water

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Step 1

Cut the lemonade bottle just below half way and ensure the edges are smooth.

Step 2

Remove the lid from the top half of the bottle and then hold the bottle so it is upside down. Place some cotton wool in the neck and position the inverted top over the base of the bottle.

Step 3

Pour in 8 to 10cm of sand over the cotton wool.

Step 4

Ensure the filter is stable and pour through the sample of muddy water.

Explanation

A filter is a device that stops certain objects or substances while letting others through. Here the sand is acting as a filter stopping the particles of dirt while letting the water pass through.

Grains of sand are not perfectly symmetrical meaning that although they can be close together there will always be gaps in between them. These tiny gaps will let the water pass through but not the dirt and so the fine particles get trapped in the layers.

The water looks cleaner but is definitely NOT clean enough to drink since microscopic bacteria could still be in the water. This is only one stage of the water treatment process.

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