There are all kinds of dangers lurking in the water and a Great White Shark is the least of the traveler's worries. Montezuma's Revenge, the popular name for the effect that microbes in the local water supply can have on travelers, ruins an estimated 40% of overseas vacations. Don't let it ruin yours!
1. All food is to be cooked Well Done. The temperature of every bit of the juices needs to hit 165 degrees Farenheit. In America or other Western nations, you may can eat a steak Medium Rare but in the Third World you want to see NO PINK IN THE MIDDLE. Some Western style hotels and restaurants may use proper cooking procedures, but when in doubt have your food cooked thoroughly!
2. Bottled water is a must. The best is carbonated water because the carbonation process kills the microbes in the water. By ordering carbonated water you also preclude someone from putting local (tainted) tap water into your table's bottle and selling it as fresh. Be aware though that some studies have shown the outside of the bottle caps to be contaminated and of course if you pour the drink over ice then you might as well call the doctor immediately.
3. Purify your drinking water. Unfortunately, you cannot always get bottled water and you will need a way to purify what you are drinking. The most common method is to use Iodine Tablets. However, these can take 30 minutes to work and leave a bitter aftertaste. The newer method is to use containers that filter the water you are using since they also filter out any aftertaste. Magellan's has an article describing these issues and they sell the self-filtering containers you will need. Well worth the money.
4. Spicy Food as a Preventative? In the past there was a belief that spicy food could help you prevent Montezuma's Revenge. Recent studies have discounted this idea. More studies are needed but don't be surprised if after eating spicy food you have an upset stomach filled with live microbes.
5. Oops! Took every precaution and still lost the battle. Not to fear. Anti-biotics can solve the problem. Visit your local doctor or medic and have them prescribed for you.