Supposed to work well if you are running high boost. I'm sure someone has mentioned this before, but you should probably read Corky Bell's book "Maximum Boost", it's supposed to be really good. I'm pretty sure he covers water injection in there somewhere. I haven't read it yet, but I'll get to it eventually.
Look up Aquamist products then cause they are one of the few well known companies who do the water injection. You could also look into variable propane injection as well. Both will have the same effect which is lower the chances for detonation. The water cools the cylinders where as the propane is simply adding more fuel to lower the chances of detonation.
basically it injects a extremely fine jet of water in to the intake cahrge cooling the charge. there are a couple reasons for spark knock. high intake charge temp( a big problem with boost), to lean a mixture, too much timing. since i'm running 9psi with a supercharger, i cant really intercool it, and instead of retarding timing, i'm going to run water injection to take the palce of an intercooler. i was just wondering if anyone had any experice?