Dig a hole in the ground a depth of about 25 cm and 50 cm in diameter. Place the center hole empty plastic container or a wide bowl, put it around the fresh green grass and leaves. Cover with a clean hole with plastic wrap and cover the edges of land to the pit did not come out of the air. In the center of the film put the stone and gently press down on the empty tape capacity. Device to collect water ready.
Leave your design until the evening. Now gently shake the earth from the film, so it does not hit the container (bowl), and look: in the bowl is clean water.
Where did it come from? Explain to your child that under the influence of solar heat grass and leaves began to decompose, releasing heat. Warm air always rises. It is in the form of vapor deposited on a cold film and condenses on it in the form of water droplets. This water and dripping into your tank; Remember, you're a bit pressed through the film, and put the stone.
Now all you have to come up with an interesting story about travelers who went to distant lands and forgotten to bring water, and begin an exciting journey.