Science to save your life!

Picture the scene – you're laid out on a raft, the sun is beating down, your mouth feels like the bottom of a birdcage. "Water! Water!" you gasp through parched lips. The seawater surrounding you mocks back "Hah! Try drinking this matey and you'll know about it!"
But wait! What's this? You managed to grab a large bowl, clingfilm, sticky tape, a glass and a small rock before the ship sank (!). Thank goodness for that! Now all you need is to make a solar still…

You will need:

• large bowl


• short glass or cup


• plastic wrap


• small rock


• pitcher of water


• salt


• long spoon for stirring

What to do:

First make saltwater by adding salt to fresh water. Stir the water until the salt dissolves. Now pour about two inches of saltwater in a large bowl. Take an empty glass and put it in the bowl. The top of the glass should be shorter than the top of the bowl, but higher than the saltwater. Put clingfilm over the top of the bowl. You may need to use tape to make sure the seal is tight. The last step is to put something heavy right in the centre of the clingfilm, over the empty glass. That will weigh the plastic down and help you collect the water. Now you've made a solar still. It's called a still because it distills, or purifies, water. Leave your still outside in the sun. Leave it alone for a few hours, or even a whole day. The longer you leave it out, the more water you'll collect. When you're ready to check your still, take the plastic wrap off and look at the water that's collected in the cup. Do you think it's salty or fresh? Taste it – it's fresh! (make sure all the items are cleaned thotoughly before you try this experiment though!)

What's going on?

Rays from the sun heat up the salty water in the bowl. When the water gets warm, it evaporates and becomes a gas. When the gas rises and hits the clingfilm, it turns back into water droplets. Eventually, gravity makes the water droplets roll down the clingfilm towards the rock. Then the water droplets slide off the clingfilm into the glass. The salt doesn't evaporate, so it gets left behind in the bowl. Water evaporates in the same way from lakes, rivers, and oceans. The water heats up, turns into a gas, and then condenses to fall back down as rain. Now, can you distill fresh water from other liquids like cola or orange juice?

Did you know?

This can also be done with urine if you're in the desert and water is hard to come by. If you do not have a pot, you can just dig a hole in the ground, do your business in the hole, place a glass/container in the middle and cover with something (plastic bag works). The natural heat of the sand will evaporate the clean water into the glass. You never know, it may save your life!