Just do it! And post results, it doesn't mattery why! Hell of an idea!

Although in the harrier, I'm pretty sure that the water is simply used to cool the engine rather than boost performance. The hottest our turbines run is when we're running them on the ground. Stationary turbine runs the hottest and that's why the harriers carry the water for vertical non forward movements. 90 seconds of this cooling water is all they can carry.