The advice above about avoiding local tap water is good. Also, you might want to avoid salads as they would probably be washed in tap water. At hotels that cater to foreigners you might be safer but why take the chance?

I'm a medical student and travel to third world countries a couple times a year with a team of doctors. We always carry a bottle of ciprofloxacin tablets for just this purpose - taken as soon as symptoms appear, this drug can many times make a big difference. (It certainly has for me!) If your physician isn't too resistant to the idea of letting you carry around antibiotics in case you need them, he or she might be willing to write you a prescription.