This is one of the simplest and best water science experiments, and it also demonstrates the power of the sun and how it can be harvested in everyday life.
* large clear bowl from the kitchen.
* cling wrap or any clear plastic food covering
* a clean drinking glass
* food dye
* ordinary drinking water
* a pebble.
Mix water in the bowl with the salt and the food dye until you have an unpleasant looking and tasting solution. Extra ingredients can be added to the bowl to increase the unpleasant taste of the mixture. These can be any household food items such as garlic, sugar, cinnamon, tumeric, curry powder and so on.
Place the drinking glass in the CENTER of the bowl
Cover the bowl with the plastic food covering. It needs to be a little bit loose. Place the pebble on top of the food covering in the center of the bowl so that it makes a dip in the plastic sheet, which must be EXACTLY above the top of the drinking glass. Then place the whole setup in the sunshine.
Here is what it will look like:
What Will Happen?
The heat from the sun is trapped by the plastic sheet and also absorbed by the salty colored water. This makes the temperature in the bowl increase. This in turn evaporates the water in the polluted solution of water and food additives. The water vapor then reaches the plastic sheet (since hot air rises) where it condenses to form water.
The water condenses since the temperature inside the plastic covered bowl is greater than that outside the bowl. This runs down the underside of the food covering to the point where the pebble is sitting, and then drips into the cup. This water should now be fine to drink.
If pH paper or solution is available, the pH of the resulting water can be compared to that of the original solution. If this is not sufficient cause for confidence in this setup as a water purifier, vinegar (acetic acid) can be added to the starting water to deliberately lower the pH of the starting solution. This will provide a good controlled test as to whether water purification via evaporation takes care of pH differences, and show that this water science experiment is effective at producing usable drinking water.
A Handy Survival Technique
Apart from being a fun experiment for your child, this is a handy survival skill. Being able to obtain clean drinking water with a minimum of materials could make all the difference if one is stranded in a tough place. Better to know this technique than not!