It would be fun to have it for hardcore mode, and stuff. The reason I would want it is to put more of a challenge in Minecraft, bu t if it was also in normal survival it would be hard(er) than needed.
Well it would make water bottles more useful. But like other people say, this would make Hardcore mode more challenging
If you want to make Minecraft suggestions, I recommend you post them at http://www.reddit.com/r/minecraftsuggestions because real Mojang members go there including Dinnerbone and Jeb.
Water bottles, duh. :P I guess it is good, but right now minecraft survival is challenging even without, so I guess it would be too hard for some players.