I'm one of the lucky ones who seems resistant to the stomach bugs and have drank water in many places the CDC says I shouldn't have. The one time I had a case of the traveller trots was in rural Armenia that may have been more attributable to heavy alcohol imbibing the previous evening than the water. It passed (pun intended) in about an hour. I've wouldn't take antibiotics in advance because they can kill the bacteria in the gut which leads to diarrhea which is what you are trying to prevent in the first place.