water turn on boost point for base system

[Sato]

I don't run race fuel ever[I'd like to but because of cost and lead etc I don't] That's the reason for water injection and now in my area NE USA the highest octane is now 93 down from 94. I plan to now go to staight water instead of water /Methanol just to supress detonation as I feel the amount of octane added and the volume needed to reduce detonation and add power is not there compared to straight water. Please correct me if i am wrong.
My question is when is a good boost point to activate the water injection?
Sometimes I will get a detonation signal from my computer and I notice that if I slam the the throttle open the signal will be indicated BEFORE high boost is reached. Other times if I use the throttle more gradually the detonation signal does not happen. Is it the advance curve,,the boost curve[I'm making a dual stage boost controler but haven't tested it yet}
or is it the forged pistons rattling under low rpm /high boost conditions /OR is it that my water injection comes on at 14 psi and not lower?
Any info would be great,
Sato