There many factors in play. Water's best attribute is detonation resistance. It will cool IAT's some, but the evaporation point is high relative to methanol. You will never get close to ambient temps in the inlet track with water.

Methanol on the other hand will cool to well below ambient temperatures in the inlet track. Yes, the latent heat is much less than water, but the flash point is much lower giving lower ultimate temps. We have run 40F less than ambient before in the inlet track with 100% methanol. The drawback is you are adding more fuel that needs to be accoutned for.

On many cars, just adding water will cool the inlet temps a little, then adding a bit more the car will loose power. If using water solely for inlet temp reduction on a near stock car, the numbers may not be dramatic.

There is no magic pill for setup with certain ratios and cars. Each application needs to be looked at for injection system capability, car use, tuning capabilities(ECU) etc. I have seen 100% water work great on some cars and applications and the complete opposite on other cars.