Well, I’d first like to know where the people who state that cold water is definitely good to drink while exercising to please state your reasoning and have scientific research to back up your claims. Aren’t you supposed to be hot and sweat after exercising? How would giving your body a sudden jolt of cold be helpful? As far as overheating is concerned, your body naturally cools itself down through sweat. If your body is in danger of overheating, then it is too hot and you shouldn’t be doing whatever you are doing in the first place! Again, please state scientific reasoning backed with research as to the beneficial effects.
Now, I will state my opinion but, as I have no research to back it up, it is just a theory.
Your digestive system is not designed to cool things down. When, before the invention of ice, refrigeration, and the like, did your stomach have to heat up ice cold water? If you lived in a cold environment, I don’t think you’d be wanting to drink cold drinks; you’d warm them up first. And, if living in a hot environment, before the invention of ice, you’d have no way to cool the drinks down the way we do now.
Now, how harmful, if at all, drinking cold water is is debatable. However, if your body has to constantly be heating up water all the time, how draining on your digestive system / body is that over years and years? Have you noticed how much heat it takes to warm up a glass of cold water to the temperature of your body? Just because you don’t feel anything bad or notice anything at the time doesn’t mean it’s not having a harmful effect.
If you want to do a little test, go drink warm water all the time for a couple months. After doing this, go drink a nice glass of ice cold water and see how “good” you feel.
As far as I know, there are no long term studies to this, so it’s hard to say if there’s really much harm to it. But, from both an Eastern (stated in earlier posts) and Western point of view, it seems to be a little harmful, in the long run.