Water in the large cities is adequately treated; if you have any doubts, stick with bottled mineral water in rural areas.  Some people suffer a bout of diarrhea just changing countries. Our advice is to observe the following measures: avoid uncooked and/or unpeeled fruits and vegetables, raw seafood, and food sold in the street.  These same precautions will also provide some protection from hepatitis, typhoid, and cholera.  The CDC does not recommend shots for cholera, since the protection they provide is too uncertain.