what's all these crazy questions there askin me?
At one time, a very long time ago, there was a difference-yes they both used liquid, usually water, but sometimes people where known to put other substances in the water to add a little kick.
A bong was a bong, like I am sure you are thinking about.
A water pipe was more elaborate, with a tube coming out of the water with a mouthpiece similar to a cigarette holder used to inhale the smoke that was chilled by the water. It reminded me of something you would see Gomez Adams or perhaps someone in a movie set in Turkey smoking.
I knew of people who would make either one at home, using bamboo for bongs and using quart jars to make a water pipe.