Here is some juice to drink :
Water Injection theory & Defintions :
http://en.wikipedia.org/wiki/Psychrometrics
What is WET Bulb Temperature :
http://en.wikipedia.org/wiki/Wet-bulb_temperature
Relative Humidity Info :
http://en.wikipedia.org/wiki/Relative_humidity
Evaporative Cooling, the effect of Water injection :
http://en.wikipedia.org/wiki/Evapora...cal_principles
Info on DEW point :
http://en.wikipedia.org/wiki/Dew_point
Psychrometric Chart : The practical elements plotted on a graph. This graphs shows you one of the most important things of water injection. The less humidity, the more is the cooling effect difference between the Dry-Bulb (Ambient) Temperature and the Wet-Bulb Temp.
Understanding the Psychrometric Chart :
http://www.swst.org/meetings/AM05/peralta.pdf