I often drank tap water straight when I perspired so much playing football(soccer). I didn't get a running stomach from doing that, although I would prefer bottled drink on any day~
It's a long time ago when i last ventured under a faucet. I think that says something about the drinkability of tap water in Beijing. You can get away with taking small amount each time though, until the effect is proved otherwise.
Before I went to university, I kept on drinking well water and tap water. I was health all along. But now when I directly drink the fresh well water or tap water again, I will feel a stomach ache. AI--, a weak constitution.