This might help....
When air is compressed, it heats up; and when air heats up, it expands. So some of the pressure increase from a turbocharger is the result of heating the air before it goes into the engine. In order to increase the power of the engine, the goal is to get more air molecules into the cylinder, not necessarily more air pressure.
The intercooler is just a radiator to cool hot air coming from the turbo.
A water spray kit just sprays the intercooler with water, a water injection kit sprays water into the intercooler piping. The spray is a fine mist so it wont hydrolock the engine.