alcohol bongs are retarded. I always had a laugh at the guys that did that - UNLESS you are going to drink the alcohol later - but that is gross considering that you use a bong to get the tar and such out.
(retarded because the THC will get pulled out by the alcohol, so you won't be breathing in the one thing that you want from the smoke)
warm water filters out the nasty shit (tars and whatnot) in the water better than cold water does.
cold water will help cool the smoke so it is much less harsh on the lungs.
hence the development of the multistage bong. (warm chamber or chambers to get the gunk out, and cold chamber or chambers to cool the smoke to make it easier to inhale a lot)
the downside of a multistage bong is that as you add stages to it, it becomes increasingly difficult to draw anything through it.
I never really cared about smoking pot since it doesn't really have any effect on me (I get really paranoid that people know that I'm hungry - but I experience zero "high" feelings) - but I like engineering.
so Soph year in college we made "The Octopus" which was an 8 stage bong made from used 2Liter bottles of Coke and aquarium tubing.
That was too hard to draw from, and entirely overkill - so we tookit apart, added more aquarium parts (like an air pump), reduced it to a 2 stage bong with 4 pull tubes, and obviously the air pump allowed a forced pressure system so you didn't have to pull all that hard (or at all really).
we called that one "The Aquarium"
that eventually broke and they ended up just using individual 2L bottles as the bongs.