I ran water injection on my '66 Corvair Corsa because the premium gas in
the 80s wasn't good enough to run the full stock timing.  With the water
injection on, it would completely stop the pinging under load.  It actually
worked very well, because you could have full timing advance for better low
end driveability and gas mileage.  It had two vacuum (pressure) switches to
measure the engine vacuum (load) and a rpm input from the coil.  As you
stepped on it, the box would vary the electric voltage to a small pump.
This fed H2O directly to two orifices pointed straight down the two primary
carb's throats.  (I had the four carb engine, with the big valves and 9:1
CR. 140 hp!)  I had the whole system wired to an on/off switch on the dash.
You didn't need it at all until the engine got hot.   You could flip it on
and  hear the pinging disappear.  It also kept the carbs, intake and valves
exceptionally clean!

                                                                        Jay