apologies for the hijack, malibu81 is there a reason your go to says water over meth injection? Did he tell you specifics of where to inject it, under what conditions and size of jet etc etc?
From what I have read the meth is to cool the intake charge which is not needed for nitrous. The water is to cool the combustion chamber to prevent detonation. I've seen both fogger type and plate type systems, I think plate type would be the one I go with. My guy has a system that comes with a water tank, regulator, plate and lines. It uses the nitrous to create the pressure in the tank.
I have read that some people swear by it and some people don't. I think its like anything else, you have to see if it works for you.
I don't know any specifics because I'm not that far yet. Feel free to call the guy I use. Jeff Prock - Prock Performance 704-660-5060. He's know a ton about nitrous and could help you out.