I thought they carried some concentrated wine-like because and mixed it with water to make the water potable. I’m surprised to learn they only drank wine sporadically.
There’s really not enough alcohol in wine, especially Roman-era wine, to make it an effective disinfectant for bad water. Hell, even vodka won’t do the job (not that Romans had distilled spirits).
This - that pre-modern people didn’t drink water - is one of those history myths that I wish would just die in a fire. At least the “medieval peasants had to drink beer” variant involves effective boiling, this version doesn’t even have that.
They drank posca because they thought it was better than drinking just water - and it is, but not because of germs. It’s a good drink.
Ignorance fought.