No doubt you will get to the bottom of your issues, my H2 was a pain earlier this year with the oil pump and ignition issues.
Took a long time to solve but got there in the end, your misfire could be something a simple as a plug breaking down - no doubt you have swopped them around to try that.
Where are you loosing water? Probably a stupid question because if you knew that you would have fixed it.
Anyway I am sure that a man of your experience will get it sorted.