Perhaps I was too strident in my criticism of your substantial comments; I apologize.
However, I am still unconvinced that people in the past viewed beer as a replacement for potable water rather than a food-like complement to it. If water was generally regarded as less safe than beer, why were so many people brutally executed for messing with it? Why do we have so many sources noting with far more sensitivity than most have today to where you can find and drink water without boiling? Surely it is not a coincidence that springs whose water you didn't need to boil later grew towns and cities? Why do we have so much evidence of what amounts to seasonal boil advisories? Why was disease so strongly associated with the presence of armies if people weren't consuming the water that forms the natural vector for transmission?
I have no doubt the confidence to which we can say water was safe could be exaggerate in order to dispel the myth that people didn't generally drink water at all, but even today people drink from water sources that would make you or I sick without becoming ill themselves. Perhaps there is room for degree of safety that might explain how water can both be safe and unsafe.
My concern is not with doubt in the consumption of beer (or wine, or later liquor) but with the widespread impression that people in the past simply didn't drink water. Such a poor understanding of what you clearly understand is a complicated topic harms our ability to empathize with our ancestors.