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 DESALINATION
 

To demonstrate desalination through evaporation:

- put half a centimetre of salty water in a tank
- place an empty jar in the middle of the tank
- cover the tank with a layer of clear foil-wrap - make sure it seals the salt water by using an elastic band
- put a small pebble in the middle of the foil-wrap, directly over the jar, so that the foil forms an inverted cone over the jar
- stand the tank in the sunlight for a day - do this in the summer!

Any water that collects in the jar should have lost its saltiness.
 FILTRATION
  Most water-cleaning plants use some form of filtration that mimics the natural filter beds of the earth. To make a simple filter:
- Cut off the bottom of a clear plastic bottle
- Fasten a piece of cloth over the neck of the bottle using an elastic band
- Tip the bottle upside down
- Pour a layer of cleaned pebbles into the bottle
- Cover the pebbles with a layer of coarse sand
- Add a final layer of fine sand
- Check the filter is clean by pouring several pints of tap water through it

Now make a mixture of soil and water. Pour this dirty water through the filter. Does it come out clean(er)?
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