You shouldn't have a big problem in China if you just stick to bottled water (which is available for cheap anywhere), just make sure the seal is not tampered with or anything like that, but that is not a big problem at least not in Beijing. Soft drinks etc are all safe. Food, if the place is packed with locals you can assume it is safe.

And at PEK airport you can get free drinking water at the dedicated stations scattered around the terminals. Had no problem with that.