If you haven't checked it out yet, you ought to go take a look at the detailed write up on water injection on the main page of this site. Most of you questions will likely be answered.
http://waterinjection.info/
The short answer to your question is yes, WI can be used on both NA engines and Forced Induction engines. It is most effective in situations were the engine is limited by knock at high power outputs. This usually means it is most applicable to high performance high compression ratio NA engines, or moderate compression ratio engines that are prone to detonation due to design or method of use. (ie. towing up hills etc.) and almost always beneficial on supercharged/turbocharged high performance engines.
Larry