Here is one major reason it does not work.
If the outside temp is 90 degrees, the water injection temp will be about 90 degrees. So there is no benefit from cooling. ( you actually will lose HP )
See on a turbo car when you have inlet temps go up the intercooler cools of the air that is beeing compreesed,( as we know the more you compress air the hotter it gets ) but the intercooler can only do so much and spraying water into the mix can help even more.
The problem with an NA car is when you spray water in you are taking up a large amount of space for water that could be taken up with air to make more HP. So even if you did spray cooler water in, the change in air temp would be offset by the percentage of water to air ratio going down less air less HP.