The most common health problems:
Stomachaches, stomach problems, diarrhea, stomach cramps, bloating, malaria (in some jungle areas .. NOT ALL!), and dengue.
Sanitary precautions and health services

We recommend that you don’t drink tap water. If you order juices, ask that they be prepared with milk instead of water, without ice. Most cities now have potable drinking water from the tap but, as a traveler, you still won’t be accustomed to the different bacteria a tropical country has. Drink bottled water when possible, and ask for carbonated water because then you’ll know it’s safe (Agua con gas) and hasn’t be re-bottled.