Mexican tap water is treated, but it’s generally considered unsafe for drinking in most parts of Mexico. Most people buy purified water in bottles. If you are living in Mexico long-term, you can have large plastic jugs delivered directly to your house. In addition, grocery stores sell water purification droplets, which can be added to tap water to sterilize it (though some add a slightly unpleasant taste). You can also make tap water safe for drinking by boiling it for several minutes to kill any bacteria or parasites, though this process does not remove any additives or chemicals.
In restaurants, you will rarely be served anything made with tap water, including ice. Most Mexicans do not drink tap water themselves, and they do not serve it in their restaurants or bars. Bottled water, like all bottled beverages, is always safe for drinking and is available almost everywhere.
Visitors to Mexico may experience gastroenteritis, a mild stomach upset that is usually called traveler’s diarrhea. Diarrhea can be caused by bacteria, a virus, or a parasite, and it usually derives from contaminated food. It can also be caused by simple excess (a few too many margaritas one night) or a change in diet and water source. Over time, your stomach will likely adjust to the new water and diet in Mexico, and you will likely be able to expand your eating.
In most cases, you do not need to see a doctor about diarrhea. Symptoms should clear up with a few days of rest and hydration. You can help avoid stomach upset by properly handling food, frequently washing your hands, and eating in places where hygiene is taken seriously. Some travelers also carry small tubes of alcohol-based hand sanitizer to use in markets and street stalls.
When eating raw vegetables and some fruits in Mexico, it is best to disinfect them before consumption. In some cases, leafy vegetables, berries, and herbs may contain residual bacteria from watering or handling. For raw consumption, supermarkets sell several varieties of food sanitizer, the most common of which are made with chloride bleach or colloidal silver. If you plan to cook your vegetables, you do not need to disinfect them; the heat will kill any potentially harmful substances.
There is always more risk associated with food stands located outdoors or in marketplaces, where hygiene is more difficult to maintain. Many people are able to comfortably eat anywhere in Mexico, while others become ill after eating in markets or on the street. Use your discretion and introduce new foods into your diet slowly.
Excerpted from the Second Edition of Moon Living Abroad in Mexico.