具体原因大家已讨论得非常清楚了。只补充一点，说中国人习惯于喝烧开过的温水，可能更加确切。

@curtis It's much more than a survival technique. It's also a custom in Taiwan, where the water is potable, and among Chinese expats (and their kids) living all over the world in places like the US, UK, Canada, etc. where tap water is perfectly safe to drink.

I see a lot of answers pinning it down to cultural differences or physical differences, but the answer is simply that tap water in China is not potable! If the water is boiled, they know it's safe to drink. Ice cubes in restaurants are very dangerous because you never know if they were boiled first. But since they learn this survival technique from a young age, it becomes cultural, and so Chinese will try to explain it as a difference in the bodies of Chinese and Americans, even though ABC's can also drink American shower water like anyone else :D 

中国人不是也吃冷菜嘛？！至于开未。

可能跟中医理论有关吧，指寒性的东西对身体不利，而温性的东西可促进血液循环和新陈代谢。