Or lack of phase change - as long as it is present, and acting as a heatsink to keep chamber temps from going high enough to detonate, then it's doing it's job. That's why people often add a lot of timing while injecting water, as it is smothering the combustion reaction so you have to light it off sooner to place peak pressure at the optimum rod angle. Same shit, different day.
There is some conjecture that injecting not enough water and detonating is actually bad - when chamber temps are too high (detonation) the hydrogen and oxygen that normally forms water as part of the run of the mill (no water injection) combustion rxn cannot join together to form water, so instead they seek out higher energy reactions with aluminum (and to a lesser extent iron). This is why detonation results in pitted craters in pistons (or tiny pinpricks in the carbon coat when timing is advanced a little too much, or when approaching knock limit for a given octane), as well as pressure spikes several times non-detonation combustion pressures. Detonate with an extra payload of water, over and above the amount gasoline brings to the party, and you have more volatile shit to consume fragile aluminum.