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If water is dirty, how can you clean it?
What you need:
- 2 litre plastic fizzy pop bottle
- Scissors
- Tablecloth or dish towel
- Gravel
- Sand
- Cotton wool
- Dirty water (you can make tap water dirty by adding food
colouring, cooking oil, small bits of plastic or soil)
- Glass
How to:
Ask an adult for help using scissors. Do
not drink the water, even when you have filtered
it. It will still have bacteria from the soil in it.
- Cut the plastic bottle in half. Turn the top half upside down
and put it inside the bottom half.
- Put the tablecloth in the plastic bottle. This is your filter.
Pour the dirty water through it. What does the filtered water look
like?
- Clean the plastic bottle. Make another batch of dirty
water.
- Try using different materials as a filter. You can use gravel,
sand or cotton wool. Which combination makes the water look
cleanest?
What's happening?
Your filter gets rid of solid large particles that are not
dissolved in the dirty water. The size of the particles that can be
removed by filtration depends on the size of the filter you
use.
A filter with small holes will stop more particles getting
through than a filter with large holes.
Your filter won't get rid of food colouring, because food
colouring is dissolved in the water. A technique called
distillation is used in laboratories to get rid of substances
dissolved in water.
The water you drink from taps is cleaned by lots of processes.
Filtration is just the start. The water is also disinfected to get
rid of microbes.