You will need:

• Large glass mixing bowl
• Small heavy based tumbler
• Boiling water (be very careful!)
• Cling film
• Small pebble or weight
• Somewhere safe to leave the demonstration for children to observe safely.

Put the tumbler inside the mixing bowl and pour in a small amount of boiling water (the tumbler must be in centre and not float). Cover the mixing bowl completely with cling film and place small pebble in the centre to create a slight slope to drain any condensation into the tumbler.

As the water evaporates children can see it condensing on the cling film and collecting in the tumbler. Older pupils can measure total quantities of water involved, use sea/salty water to create pure water etc.

This works a treat for all ages, although the learning depends on the quality of the discussion generated.