From what I understand, the "safe drinking water was a pain in the ass" thing is largely a myth. Some good information available in this r/AskHistorians Reddit thread: https://www.reddit.com/r/AskHistorians/comments/1svj1q/how_d...

I believe it varies from region to region. In my country natural springs are all around so fresh water is not a problem. But I remember reading medieval era memoirs how people get surprised traveling when others don't have as much access to springs.

The article says that the bad water theory is unlikely because it's easier and cheaper to boil water than to make alcoholic beverages.