With all 4 stroke engines you can add a certain amount of water to the incoming charge to boost performance.
In every case you can expect to need less fuel.
At max performance most engines are overfuelled past the point of being a chemically correct mixture.
Some of this excess helps cool the motor, now if you replace the excess with water for the cooling effect, you can then correct the fuel mixture for best combustion efficiency and hence a power increase.
Again simplified.