We went to Vietnam when we were TTC, and I actually missed AF about 2d into the holiday. I didn't change anything until about 5w pregnant I spose, cause I had some implantation bleeding I thought was my period.
Before that I ate street food, raw oysters, lots of fish/shellfish, drank heaps of beer and alcohol and generally lived it up. It was a blast!!
After I was about 1w late, I decided I really could be pregnant and started doing everything a little more carefully.
As for drinking bottled water, thats a given. I would do that regardelss of whether I was pregnant or not.