The above video shows a simple method to obtain pure (almost drinking-quality) water, from impure water, using just the sun's heat. The concept is quite simple: Water evaporates due to sun's heat, leaving all dust/debris below. Due to the plastic cover, the water vapour cannot escape into the atmosphere. So, it gets condensed back into water, slides towards the middle and then drops into the empty smaller container placed in the center of the larger bowl containing the impure water.
The plastic cover ensures that sun's heat gets trapped within the container (due to glasshouse effect) and heats up the water to form vapour. This principle is the same as pure water evaporating from the sea (leaving off all the salts), forming clouds, and falling back into the earth as rain. As you can see in the video, the set-up is simple and it could be very useful in places where water filtration is not possible. In countries closer to the equator, this should work for most months, not only during summer. This method of obtaining pure water using sun's heat is referred to as solar stills.
The solar still can also be used to make water, if there is no water available (emergency situations). The second video (embedded above) shows how you can do that using just a simple plastic cover, some edible plant leaves, a container, and some stones. Actually, our soil stores some moisture that evaporates into water vapour (if enough - sun's - heat is available) which evaporates & condenses back into water. This water can be trapped in a container placed at the center (just below the central stone on the plastic cover). So, next time you find yourselves stranded in an island or sea or forest or where ever, you know how to get pure drinking water!
