Fresh water from the sea: designing a solar still
Answers are for parents and teachers.
1
Draw the water cycle with the sea, a cloud and rain. Label where evaporation and condensation happen.
Evaporation labelled at the sea surface; condensation labelled where the cloud forms; rain falls back to the sea.
2
A still collects 18 mL each hour in strong sun. How much does it collect in 4 hours?
4 × 18 = 72 mL.
3
Explain why the cup must be lower than the rim of the bowl in our design.
So the drops that run down the wrap fall into the cup and not outside the bowl.
4
Draw your own better solar still and label one change you made to improve it.
Answers differ, for example a darker bowl or a tape seal.
5
Write a claim, evidence and reasoning to answer: how can the Sun help make fresh water from sea water?
Claim: the Sun’s heat can make fresh water. Evidence: our still collected water in the cup. Reasoning: heat makes water evaporate and leave salt behind; the vapour condenses on the cooler wrap and drips into the cup.