Water injection in one form or another has been around since early pioneer motorists noticed their early Edwardian internal combustion engine powered vehicles performed better on cold misty mornings. By the 1920's engineers had also understood that pushing air into an internal combustion engine above atmospheric pressure using a compressor was a great way to increase performance, forced induction also started to make a lot of sense on aircraft as they began to climb higher and higher, as we all know air becomes thinner at high altitude.
However, when you compress air you also heat it, so water injection was again used to lower the temperature of the incoming compressed charge of fuel and air. By WW2 things were getting really serious, to gain the advantage pilots need to be faster and fly higher so most fighter aircraft sported forced induction, typically a centrifugal vaned supercharger was used as with the Merlin V12, or turbo charging as seen on the 12-cylinder Allison used in the Lockhead P-38 Lightning.
As boost pressures increased so did intake temperatures, and to the point where engine destroying knock (detonation) became a real problem and as a consiquence water/methanol injection became essential. By the early 60's Chrysler were experimenting with turbo charging their passenger cars, to solve the detonation problem they also used water/meth injection on their Oldsmobile Jetfire model that ran the Turbo Jetfire engine.
After this intercoolers became more common, but water injection has more recently returned on the BMW M4 GTS that utilises water/meth injection in conjunction with intercooling to keep the engine safe at the higher boost pressures BMW wanted to run. Water injection is as old as the hills, it's also proven in combat and on many road and race cars. Not only does it lower intake temperatures which is especially helpful where a compressor is used as you can increase your igniting advance without destroying the engine with knock, but when the water enters the hot combustion chamber it immediately vaporises to steam creating an increase in cylinder pressure and so an increase in performance too.
It also keeps piston crowns, valves and combustion chambers spotlessly clean
