The more common version of this, which I do remember hearing in history courses in college, was that people in the Middle Ages frequently mixed beer or wine with water. Whether that was done purely for taste, or in the belief that it would make potentially unsafe water safe, and what the details of making water safe to drink by mixing beer or wine with it actually are, I don't know. The author himself makes this point repeatedly, that water was frequently mixed with wine (at which point people are drinking watered wine).

It's like there are two parallel arguments:

"Medieval Europeans exclusively drank alcoholic beverages, because the water was so bad." And,

"We currently over-estimate the degree to which people in the Medieval-era consumed alcohol, and under-estimate the degree to which they drank pure water."

The author seems to conflate the two willy-nilly, claims the first to be widely held, and that he has disproved it (while, among others, citing Classical rather than Medieval sources).

Interestingly enough this is my first time hearing about this whole drinking alcohol theory and its whimsical

I always understood the myth as: "When you traveled somewhere and didn't know about the water-quality, you drank beer instead".

Not that beer is immune against making you ill, but chances are random beer in some random village is better than random water in some random village, since the village people would use the good water for the beer.

The idea is by making it beer you keep safe water safe for longer. It doesn't sound particularly weird to me (I don't know if it was really a common practice in medieval Europe.)

As someone who until recently had believed this myth and had never tried home brewing, the theory was that the alcohol kills the bacteria

> I always thought it quite weird that somehow by virtue of being in beer, that the water somehow becomes sterilised.

The reason that water in beer is sterilised is that beer is brewed — i.e. boiled.

> If you've ever tried home brewing, you'll know that non-sterile conditions lead to foul rancid filth due to all the bacteria etc.

I believe that pre–germ-theory brewing practices tended to discourage unwanted microbial activity, in part through inoculation with large amounts of fresh barm. Did they put two and two together and connect those practices in the context of brewing to the broader context of water or food safety? Maybe.

> I'd find it odd if the people then knew to sterilise the water and equipment to make beer, but then not do the same to drink it.

Indeed, the article quotes Paulus: ‘But waters which contain impurities, have a fetid smell, or any bad quality, may be so improved by boiling as to be fit to be drunk.’

You don't really need sterile conditions, yeast just need a head start to outcompete other microbes. Then, as alcohol and CO₂ build up, the brew becomes bacteriostatic. Which is still different from being bactericidal.

I think it's a traveling tip like "always ask for halal option - they have better ingredients" or sth.

People know beer needs specific conditions or it doesn't sell. So they are careful about that.

If you ask for water you might get the water they use for cooking soup or cleaning the mugs and they might not boil it beforehand.

Also, beer production started with boiling the water. So in a sense you sterilize the water and the beer helped preserve it for storage.

Watering down wine was also common in the era though, and the mechanism there implies the alcohol and acidity of the wine acted as a minor sterilizer.