in your type of cases where fuel is a given issue (ie inconsistent) i would strongly reccomend running a remap of the std ecu, we have a few running high 300kw's on them without issues and the benefit is if you do get a batch of crap fuel the knock map will go a long way to saving your ass.
The main usage (but not always) for water meth is actually to get MORE agressive with the tuning, the issue is if the w/m stops working you are left with a fairly hairy issue. If your lucky and have an ecu with relevant GPO or GPI's you can set the warning on the WMI to switch to a low octane map.
Even if you use the system to stop your current knocking issues with water meth the underlying problem is still there if it ever fails to operate. Fix the underlying issue, or be vigilant with WM levels
either way the only sytems to use are available from rocket and here is the systems website. http://www.snowperformance.net/