Are you looking at water spray water injection. Both very different.
If its water injection I suggest you get a NOS fogger, 3 NOS brass injectors (.25, .30 & .35 for tuning the thing), a decent pump that can pump water at a high pressure, an adjustable pressure swith for low pressure 1-30psi should do it from Honeywell=$50, an incabin switch, wiring and tubing etc. You can even put a bit of alcohol in the water 50% of each normally does the trick(help the water to atomise)
Set the water injection to come on about 3-5psi before full boost. This will elliminate any chance of major detonation at high boost by cooling the charge and making the air more dense. MAKE SURE YOU NEVER RUN OUT OF WATER WHILST RUNNING AT HIGH BOOST.
If it is intercooler water spray you are better of having the water come on when the car is stationary so the water combats heat soak and also to continue the spray upto about 60kmh so that the air travelling into the core hits the water and cools the cooler.
Hope this helps,
Doc