To save the next person spending the time I have...
The video clip shows someone's project. It starts with a small bowl full of water, covered with some plastic food wrap to prevent splashing. When someone touches the surface, the connected computer makes noises a bit like a drum. Different touches, different places: Different sounds.
No tech specs that I could find. There's a reference to Max/MSP which appears to be a programming language. One that Arduino people have worked with, although the video clip doesn't involve one. Nothing that I could find about even general specs of what is being measured in the water to be turned into the sounds.
Capacitive sensing might be something you could use for this. Do you want to detect the presence of moisture because you get special capacitive sensors that are used in storage tanks for example.
Thanks zageek, it can be.. but I don't have experience about electronics, I'm looking for some sensor that detect any kind of moves under water, I want to detect specific when for example a fish is swimming inside the fishbowl.
It should be sensitive enough to register your hand in the water.
David
[edit]The video says that he is using piezo sensor to capture the sound of the finger/waves/drops in the water
The piezosensors are cheap and easy to find[/edit]