This infographic gets down and dirty about where the water is drinkable, lest Montezuma's Revenge make a visit upon you.
NeoMam Studios has pulled together an interesting diagram about worldwide water safeness, collating information from the Center for Disease Control (CDC) and the World Health Organization (WHO). Some regions clearly fare better than others: for instance, Western Europe trumps most of Asia but it doesn't mean you can't drink the water in Hong Kong or Singapore. You might want to watch out if you're in Africa or South America though.
That said, I still know people who wouldn't drink the water in Florida.
