Water injection

[T&C]

I have an urS4 that has an old Hoppen stage 3 kit on it, 2.5 bar instead of
the 3.0 bar map sensor.  But on the California reformulated gas I still get
pinging under high boost/acceleration.  I was first wondering if this is
possibly a problem with a bad O2 sensor or something rather than just bad
gas, I always use 92.

If not, what about an ERL Aquamist water injection system.  Anyone have any
experience with one?  Especially tapping it into the map sensor to actuate
it.