When traveling we pretty much drink and eat as locals do although as vegetarians we don't eat meat or fish. In particular I take my cues from cleanly dressed ladies when it comes to selecting food stalls, restaurants, or street vendors. The fact we are vegetarians and we travel with Ciproflaxin for major episodes and a Chinese medication for minor upsets makes us pretty liberal with food and drink.
For water, we drink tap water from the hotel if the locals say they drink the town's tap water, and we almost always use tap water for brushing teeth. When tap water is considered non-potable, we get or boil our own water (as in China), get filtered water from hotel (pretty rare), fill from hotel's water cooler (not very often), or buy water as a last resort in order to cut down on the amount plastic we use. Our family mule not only goes through a lot of feed, he can drink a lot of water each day. When we do buy water, we buy the largest size bottle we can comfortably handle. For this trip, we have been able to get 5-liter bottles in Ecuador and 5-liter bags in Colombia, which we decant into our two, 1-liter nalgene bottles: one wide-mouth and one narrow-mouth. We also carry 2 small metal mugs.
Our strategy has worked pretty well in general, except John got parasites in Burma which he got over by himself. In fact he did not even know he had them until well after he was all better. I got parasites in Nepal which took me a while to diagnose and had to take medication.
This trip we have been doing well so far. We have been mostly over 2000m (7000ft). It is either sunny and dry or cold and wet, not very conducive for bacteria growth. Besides, boiling water does not help as much, since water boils at lower temperatures. We can even tell just from drinking boiling hot coffee which seems to be "ready to drink". Even at lower altitudes I suspect people are pretty apt to use pesticides. Lastly the population density in the New World is not same as the Old World; that makes everything better.
