If one was faced with water of dubious potability, how much 200-proof alcohol would one have to add to it to make it sterile enough to drink safely?
According to one link, exposure to 70% ethanol solution for 10 minutes is sufficient to sterilise some medical equipment. So you will need about 1.5 litres of 100% ethanol to sterilise 1 litre of water, and the resulting mix will be 140 proof.
Anyhow, if you have pure ethanol available, why would you want to dilute it with dirty water :smack:
Si
And a further cite that shows that sticking a dirty water icecube in 86 proof Tequila (43%) is not sufficient to kill pathogens.
Si
I could have told you that. I know for a fact that there isn’t enough alcohol in a Bloody Mary to counter-act the pathogens in a Baja ice cube. :smack:
Yeah, but those geniuses actually got paid to find that out, and bragged about it in a respectable publication.
I want a job like that. 
Si
So you can drink it. You sure as hell don’t want to try ingesting it straight.
Now, if you’re using it as a reagent for certain lab processes, then you do indeed want it pure. You can get a whole liter of 100% ethanol for $105.
If your water contains enough alcohol to efficiently kill bacteria, it contains enough alcohol to kill you.
Small sips, and no smoking. 
The risk with high-purity ethanol is overconsumption - people get the math wrong, drink too much and poison themselves (and, sadly, others). So this is not a recommendation to try (I certainly never would), and it is actually difficult to get hold of without added denaturing agents (I’m betting you need a license to order the stuff linked above).
Si
Hmmph. There goes my best party trick. 
People look better with eyebrows
Si
So, may I infer from this (following the “never freeze again what has been thawed” rule) that pulling a vodka bottle out of freezer, letting it sit one day outside, putting it back in the freezer, is unsafe ? And the more it is done, the more pathogens end up in the bottle 
?
Not quite. Liquor apparently won’t be enough to kill all of the large amounts of added pathogens. The alcohol might be able to kill 99.9%, and prevent replication in the remaining 0.1%, but that’s not enough if you’re adding millions of nasty microbes via a dirty ice cube. But it’s enough to prevent the odd pathogen that falls into the bottle from growing to even a mildly hazardous level. So unless you’re in the habit of mixing lots of dirty things into your vodka, that bottle should be safe indefinitely (well, as safe as vodka ever is…)
Alcoholic beverages that are made without distillation, such as wine and beer, can’t get to their level of alcohol without bacteria surviving to generate it. So, the minimum alcohol to make the mixture sterile is at least that high.
And (from my experience with a bottle of schnapps) it should not be frozen anyhow - 80 proof alcohol freezes at -26[sup]o[/sup]C.
Si
We used to supercharge vodka in the winter, you just need a piece of V profile plastic sloped at a low angle; pour at the top, the water freezes and the pure stuff runs out of the other end. …for health reasons of course, water being filthy and all that. Also, if you want to sneak a bottle somewhere, the less water, the smaller bottle you can use.
Wine and beer are made with yeasts, which are more sensitive to alcohol content than bacteria.
Si
Ooops - right. My mistake!
Okay, if you drink 140 proof water, is it really safe to drink, or if you drink 140 proof water, you simply no longer care whether it’s safe or not?
There’s no such thing as 140 proof water – “proof” is not used to talk about water. There is 140 proof alcohol.
Kind of of ends the theory that people used to mix water and wine to make the water safe to drink.