I just uploaded a new video tutorial on youtube about waterbased timers in minecraft (for e.g. mobtraps). I will do the english version as soon as possible and post the link here beside the german version.
For Questions I recommend to use the board at my nook.

German Version - Minecraft - Wasserbasierte Timer

Edit: Now the englisch version is up, too. If you have any questions feel free using my anook Board.
Minecraft - Waterbased Timer