Cooler water yields cooler smoke, but warm water has a cooling effect as well. But cold water solidifies the THC faster, causing it to remain in the bong.
The only way to find out which will create your perfect hit is to do what we did: experiment!
Just keep in mind:
If you’re going to experiment with warmer water, don’t go above the temperature of an immediately drinkable cup of tea. Too much steam can burn your throat.  Whichever temperature you prefer, always change your bong water after each sesh! Leaving it to sit is a recipe for bacteria and grime. Fresher water equals fresher tokes.  Glass bongs are sensitive to sudden temperature changes. Don’t pour hot water into a cold bong or cold water into a warm bong! Run the piece under lukewarm water first.