Great for wealthy kids to learn about water evaporation and condensation… or poor developing countries where clean water is a real concern.  The WaterCone is a simple and neat way to turn brackish or salty water into potable drinking water. 
Or you could always get the Watermill or the Lifesaver water purification gadgets.

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I like this product… solves a couple of problems in one tidy device. In many third world countries they have to travel quite a ways to get dirty water, then tote it back to their hut house to boil the water before using it. Seems like it might easier to just use a [...]