When my cousin lived in Equador, she ended up getting a little UV light to sterilize her water before she drank it. That seemed to help a lot, as before she was constantly getting sick from the water, even when it was cooked in foods. She ended up having to sterilize all her water, even that which she cooked with. I'd invest in a good portable water filter and use that for all your drinking, toothbrushing, contact lens washing, etc. Better to be safe than sorry!
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein
It really depends on where you are going, if they have Giardia in the water, if their sanitation is so crappy it could contain multiple contagious diseases etc... Another big concern in many countries is Hepatitis A (which is very widespread in Central/South America, the Middle East, and many other regions).
When I traveled to the Middle East the water and the blood supplies were fine but Hep A was very common and the family I visited with insisted that NO uncooked unpackaged foods be consumed from restaurants or stands (it is transmitted by unclean hands that weren't washed after using the bathroom).
Depending on the country their blood supplies may also not be clean (Hep, HIV, etc...). That may seem like a far fetched worry but not after you see the traffic and accident rate in many other countries. Spending $50 on travel insurance is often a VERY good idea, if you are in an accident and seriously injured they fly you home on a medical transport plane, they also pay a few thousand for hospital care on site (and in many places if you can't pay you will not receive decent care). You can also google to find out if various countries have a clean or dirty blood supply.