I thought for water injection to cool properly it would have to be injected into the manifold just before the ports so it cooling the already atomised fuel/air mixture. Just like NOS. I have never seen it been injected inside the airfilter probably because it wouldnt be very effective. Maybe you could drill a hole in where the two runners join on the manifold, tap a thread and screw water injectors in. 1 injector for 2 ports.

The system is quit efective actually for a suck through .The theory is that the methanol is sprayed into the su upon boost
and drawn through the turbo and atomised
with the fuel .This creates a richer mix on boost and helps with detonation .

This system works very effectively. I have run the same type of system no a few of my turbo drawthrough setups.
I not only cools the air fuel mixture but also cools the compressor wheel and that helps it atomise also, I would think it would be more efective then just firing into the ports near the head as it wont atomise as well.

But there is a problem with this system, water WILL pitt the compressor wheel over time and over time wear out the turbo faster.