While each destination presents unique risks, the most commonly reported health issues for international travelers are food and water-borne illnesses. Unlike some other travel-related illnesses, there often are not any preventative vaccinations or specific treatments for many food and water-borne illnesses. However, some careful planning and easy preventative measures while traveling can significantly mitigate the risk of becoming ill.
Food and water-borne illnesses are prevalent across the world, though they are particularly pervasive in developing nations where access to clean or running water is limited and locations where food safety regulations are non-existent or poorly enforced. Food and water-borne illnesses are even common at upscale resorts in popular well-developed tourist destinations, such as Cancun, Mexico.
The most prevalent food and water-borne illnesses are salmonella, E. Coli, giardia, cholera, and traveler’s diarrhea – which is reported by an estimated 20-50 percent of all international travelers. Travelers to rural and tropical climates may be at higher risk for traveler's diarrhea and other food and water-borne illnesses. High-risk groups include young adults, adventurous eaters, those who travel to remote areas, and the immunosuppressed. Individuals on certain acid inhibitors, known as proton pump inhibitors (for example, omeprazole and lansoprazole), may also be at higher risk for becoming ill. Individuals with chronic medical problems, such as inflammatory bowel disease or diabetes mellitus, and children may be at higher risk of complications from food and water-borne illnesses. Most food and water-borne illnesses, such as E. coli, salmonella, and traveler’s diarrhea.
The easiest and most effective way to avoid contracting food and water-borne illnesses is to pay careful attention to what you eat and drink.  Attempt to only eat foods that are freshly cooked and served hot, avoiding foods that are washed in water (such as salads, fresh fruits, and fresh vegetables). Avoid foods that sit out, such as at buffets, and avoid roadside stands and street vendors. In certain destinations, milk may be diluted with impure water, and fruit juices may be reconstituted with water. Avoid tap water and opt for bottled water instead. When drinking soft drinks or other beverages, travelers should be mindful and request their drinks without ice. 
If you do become ill while traveling, it is always best to err on the side of caution and visit a doctor for an accurate diagnosis. Many food and water-borne illnesses, such as traveler’s diarrhea, do not have a specific treatment, but other more dangerous illnesses such as cholera may require antibiotics. Generally, the most important treatment to begin at the first sign of a food or water-borne illness is rehydration. It is essential that you begin replacing fluids and electrolytes to avoid becoming dehydrated and potentially prolonging the illness. 
It is generally best practice to take the precautions described above whenever you are traveling abroad, but before every trip it is highly advised that you consult a physician for a pre-travel checkup and ensure you understand the full range of potential health risks that are prevalent in your intended destination.