A watch working liquid energy

Have you ever seen a watch that does not work with the use of batteries, adapters or wining up- systems? I had not either! But here it is: The water watch!
Without additional energy it works on the power of liquids, not necessarily water.
How? I have no clue, it might be a scientific simple solution. But hey, that's why I chose to write and spread the word! For sure it is a way to ban the apparently unhealthy electric devices out of your house.

Weight: 250 grams, size: 10 cm, 3,5 cm x 16 cm.
Until now I only found it at the Dutch Greenpeace webstore.