Bongs are rated one of the worst when it comes to THC delivery, but you are able to get a bigger hit off of them, so it equals out, also the water filters out alot of the bad shit and keeps that from going in your lungs, ie. the tar and shit. The bong is fundimentally a bowl which its stem goes into a little bit of water, then when you suck on it, you get the famous bubbling sound from the smoke coming down the stem into the water, kind of like blowing in a straw, but in reverse... pretty simple idea once you understand it, one thing i like to do when i smoke out of a bong is to crush up some ice, and put that in with a little bit of water, it supercools the smoke, and gives you an even smoother hit