I even use chemical treatment on the bottled water.

I was in Egypt and had been buying bottled water from a local store until I saw the kids taking our empty bottles, refilling them from a wall tap and popping a sealed cap onto them. They would then take the refilled and sealed bottle back to the local vendor and get a bit of change for "recycling".

Now when I travel I usually try to take my own water bottle and treat my own water. Chemical treatment is nice in that it is easy to slip into a bottle without pulling out an elaborate filter and you are not as likely to offend anyone by implying that they are giving you something contaminated.

The recommendation to take motion sickness pills is good but be aware that they can cause drowsiness so make sure you are with someone who can look out for you if you fall asleep.

In addition to Pepto or Imodium I like to have some electrolyte powder to help get the body back in balance if you get dehydrated from diarrhea or other illness.