People weren't stupid: They know drinking water made them sick with diarrhea, but if they drank beer or wine they didn't.
And I had always understood that the "beer"of Egypt and Mesopotamia was low alcohol, but full of protein from the yeast so had nutritional value: More like thick grey home brewed African beer than clear lager.LINK
Thanks LadyDoc. Egyptian beer was more like soup, and was indeed low alcohol.