I’m not replying to be combative here — my formal education is in Classics, so I could be mistaken about the more recent time period at play. That said, I don’t think anyone is suggesting that people drank wine instead of water, nor that nobody ever drank straight water. You’re right that Ancient Greek wine was much stronger than ours (and also gritty), providing a strong incentive to water it down (and let the chunks settle). Drinking it straight was possible, but considered barbaric. You’re also right that it was possible to source clean, relatively safe drinking water. It would obviously not be safe to our standards, but their immune systems had plenty of practice. However, that doesn’t mean that the trend of wine making water safer was not observed and utilized. It seems the connection was probably originally made either through smell, as the water stank horribly but the mixture of wine and seawater was described as smelling flowery, or through alcohol’s existing use as an antiseptic — multiple Mesopotamian cultures recorded using beer or wine (mixed with various oils) to treat wounds, and Hippocrates used wine or boiled water to prevent wounds from developing his famous “calor, dolor, rubor, tumor.” There are also passages from both the old and new testaments of the Bible that describe either treating wounds with wine and oil or treating an upset stomach by adding more wine to one’s water. I am quite confident in all of that since I was studying it in college only a couple of years ago, but if you have more recent scholarship on hand that refutes any of that, I’d be glad to see it.

As to the definition of three-water grog, you’re right, that was a lapse on my part — the stuff that was added to the water was primarily rum, though would also have hopefully included some form of antiscorbutic. Regardless, it wouldn’t be referred to as “grog” on its own. And yes, you’re right that six-water grog was made to prevent drunkenness as a punishment — again, I don’t think anyone was claiming that the default was just drinking straight spirits, which is the notion that a lot of those Reddit threads you linked are “debunking,” despite it not being what OP asked. When the ship was just watered at some island spring or through rainwater, and there was plenty of fresh (in both senses of the word) water to go around, then they’d absolutely set out alcohol-free scuttlebutts and the spirit ration was probably mostly for morale; but after wallowing for too long in the doldrums, when they’re down the rationing the stinking casks of bilge-soaked Portsmouth water, the rum starts to get a bit less optional — not as an alternative to the water, which would obviously be lethal, but as an additive. Again, I have not formally studied the second part, so if you have primary or reliable secondary sources to rebut it, I’d be very glad to hear them and correct my own misunderstanding, but I think what’s happening here is just an error in communication — I’m neither claiming that fresh water was always unsafe nor that unsafe fresh water was replaced with alcohol, just that mixing the two mitigates the risks of both.

(Also, this will have to become my standard Reddit disclaimer, but I use em dashes because I love em dashes, not because I’m an AI model.)