Water surface can also functions as a touch screen

Yes you can also convert the surface of the water to a touch screen.The only thing need is a web camera and a software which can detect the presence of touch.

For this actually the camera is actually placed under the water so that it can take the pictures of the presence of touch on the top of the water.Thus this pictures are processed by the software.Following that, a color tracking system on Max/MSP+Jitter finds coordinates where the finger appears while producing a cursor move and click in return.