OK... We might as well talk about it and not mince words... diarrhea....
The trots, Delhi belly, Montezuma's revenge, tourista... call it what you will, if you travel, you may have to put up with this one day.
Country and city names aside, you can get diarrhea anywhere. It may be the water... even if it isn't dirty or contaminated. Water away from home contains different minerals and bacteria than your water at home... and it doesn't matter where home is or where you travel. Americans traveling to Mexico may worry about Montezuma's revenge, but we've talked to Mexican tourists who got tourista in California!
There are countries where you shouldn't drink the water. Hotels in those countries will usually provide complimentary bottled water in your room. (Double check before you just assume this though.... both whether the water is safe and if the bottle is complimentary.)
If in doubt, go ahead and drink bottled water...better to be safe than sick. Beer, wine, bottled soft drinks, boiled coffee and tea are also safe to drink. (But skip the ice cubes.)
You can get intestinal troubles from the food as well as the water. It all depends on what your body can put up with.
To be really safe, the tried and true travelers' rule is to eat food only if it's peeled or boiled or well cooked.... a rule I'm afraid we break more often than we should. We do eat at street stalls if they look clean... but you never know what microbes are lurking....
And we eat salads even on safari or in the jungle or traveling overland in India or Tibet. Sometimes it's a matter of "what else can you do". For all the fun experiences we have being this adventurous, we haven't had all that many bouts with "the revenge".
We had an old doctor tell us that one of the best ways to ease your digestive system into the local cuisine was to eat things that are acidy and yeasty.... he suggested beer and yogurt. The yogurt abroad has enzymes that can help... and the beer? I don't know how much it helps, but it's fun to try all the local beers, and it's always safe when the water isn't.
The causes of diarrhea are just as likely be the stress of travel, the fact that you're overtired and jet-lagged, and that your immune system is worn down, so it may not be the food or the water.
If you do get diarrhea, it will usually run its course in short order. Eat bland foods, and take it easy for a day. Drink plenty of water to replace lost fluids and avoid dehydration. You can take anti-diarrheals to help slow those trots down and start you feeling better as long as you don't have a fever or blood in your stools.
Gross as it sounds, I had an attack when we were walking the Vietnamese city of Hoi An. Our driver wasn't coming back for a couple of hours, so I told our guide every time I had to "make a dash". She seemed to know people everywhere, and I was graciously allowed into the back room of businesses and several private homes to, ...ahem..., use the facilities. I wasn't too happy at the time, but in retrospect, I had a tour like no other! What a story, eh?
To re-emphasize... if the condition persists, if you're running a high fever, or if you have blood in your stools, you should see a doctor and get antibiotics.
Don't be worried about this. Try to be smart about what you eat and drink. Even then you may get "tripped up". You'll soon be over it... and maybe you'll have stories to tell too.