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I've been exploring various methods for purifying water, and I'm curious about the potential effects of adding alcohol to make it potable. Could the addition of alcohol serve as a means of purifying water, or would it have adverse effects on its potability? Are there specific concentrations or types of alcohol that could potentially render water safe for consumption, or is this approach entirely ineffective or even harmful? Any insights or studies on this topic would be greatly appreciated. Thank you!

Dino
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    what are the contaminants making the water non-potable? – Waylander Dec 20 '23 at 10:56
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    Please check your use of terminology. To purify means to remove contaminants, not to make potable. A pure substance is free of any others. – Buck Thorn Dec 20 '23 at 14:05
  • Ethanol is the only type of lower alcohols the human body can tolerate in amounts that are antibacterial. – Karl Dec 21 '23 at 21:57

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Adding alcohol to water can make it safer to drink in some circumstances

There are many ways for a water supply to be contaminated with things that are bad for people. Alcohol can deal with some of them.

If the water supply is contaminated with inorganic poisons like lead or mercury, alcohol won't help. If it is contaminated with biological pathogens like cholera, E. coli or campylobacter, then a certain level of alcohol may render the water far safer for people.

Indeed the use of alcohol to make potable, safe drinks has been the dominant method of water "treatment" in human history possibly since before cities became common.

Only in the last 200 years have people had routine access to potable water free of pathogens (domestic water supplies use chlorination or ozonation to ensure bugs are killed but those are recent inventions). Before that the safe drink was an alcoholic beverage as the alcohol levels were mostly sufficient to kill the typical pathogens. Most spectacularly, when John Snow–no, not the Game of Thrones one, the father of modern epidemiology–was collecting the data about the London cholera epidemic in 1854 to understand its source, he observed that there were no cases in a brewery near the famous contaminated pump because the workers were all given generous supplies of beer.

More about the history of alcohol in "cleaning" water is given in this Skeptics.SE answer.

For most of human history alcohol has been a major way to make the water supply safer.

matt_black
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    But microbiological safety of beer is result of many more processes than formation of alcohol itself, the most notably boiling. – Poutnik Dec 20 '23 at 14:38
  • @Poutnik That is also true. But many cultures added their wine to water to achieve the same effect. And the presence of alcohol in beer preserves the effect. And the production of some alcoholic drinks does not involve boiling. – matt_black Dec 20 '23 at 16:42
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    But then it is rather diluted wine than water, while production of some drinks does not involve adding raw water. – Poutnik Dec 20 '23 at 16:46
  • @matt_black historical beer alcohol content seems to be reported around 1%. Is that really enough to preserve anything? – infinitezero Dec 21 '23 at 06:34
  • @infinitezero i suspect that report that historic beer was weak is nonsense. I've seen the claim before but the evidence seemed really speculative and weak. – matt_black Dec 21 '23 at 11:35
  • @Poutnik The effect of adding wine to water works to reduce pathogens as does the production method of most alcoholic drinks. If the dominant drink is alcoholic rather than raw water, the effect is what matters. eg the John Snow example. – matt_black Dec 21 '23 at 11:42
  • @matt_black But in the Q context, the primary criteria is if it is still possible to call the result potable/drinkable water. Not if boiling malt to make beer, or adding wine to water makes the result drinkable. E.g. according to local law, any drink with more than 0.5% of ethanol is considered as alcoholic drink. You would need to pour 1L of wine to about 25 L of water to call it "potable water". And I would hesitate to drink it if water source was questionable, even if just microbially. – Poutnik Dec 21 '23 at 11:51
  • I assume wine acids in high dilution could be more potent in killing bacteria than ethanol, especially in water of low bicarbonate content, boosted by gradual acetic fermentation. – Poutnik Dec 21 '23 at 12:22
  • @Poutnik The legal designation of the resulting drink is irrelevant. if creating a 5% alcohol solution kills bugs, that is a big contribution to creating a safe drink. Though we now have far better ways to achieve safe drinks, this was a big factor historically and probably saved many lives from the effects of dirty water. – matt_black Dec 21 '23 at 13:29
  • Safe drink is not the same as water and it neclects chemical composition. You would not let 2 years old child to drink 5% ethanol as water unless as the last option if water itself was high risk of death or disease. – Poutnik Dec 21 '23 at 13:38
  • @Poutnik If the essence of the question was the distinction between a "safe drink" and "water" it should be moved to a linguistics site not a chemistry site. In other words, your objection is distracting from the essence of the question. – matt_black Dec 21 '23 at 13:44
  • Well, you are distracting from the fact than alcohol does not make from general unsafe water safe drink. – Poutnik Dec 21 '23 at 13:53
  • @infinitezero 2.5, 3%, not 1%. Of course stronger beer was available, but more expensive, and you get drunk. 2.5% beer is pretty harmless in terms of direct intoxication. – Karl Dec 21 '23 at 20:55
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It would not create potable water. It would create a disinfectant, with concentration higher than many/most spirits, if it should assure sufficient antimicrobial effect.

Low concentrations would additionally lead to formation of acetic acid, so there would be kind of vinegar after few days.

And, it would omit sensorical and chemical aspect to be potable water. If it was not good in this context before alcohol addition, it would not be good after it either.

Poutnik
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    Only a small selection of bacteria can grow while metabolizing ethanol of beer or wine into acetic acid and surviving the low pH environment, and none are human pathogens. Further the conversion is very slow since it requires free oxygen. We agree that modest ethanol levels in a dilution may not kill pathogens, but neither can they grow. – stevea Dec 21 '23 at 01:10
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    @stevea Well, they do not grow much in water either. They mostly stay and wait. – Poutnik Dec 21 '23 at 05:40
  • Additionally, producing beer involves boiling and wine is not made from water. – Poutnik Dec 21 '23 at 07:30
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    @Poutnik They grow, on less-than-clean surfaces, and from whatever else is in that water. With low amounts of alcohol, or vinegar (Roman "posca"), the germs have trouble staying alive, giving them much lower chances of overwhelming the defences in your stomach. I like living in modern central Europe, where the tap water is so clean they don't even chlorinate it at all. But in ancient Rome, or Lutetia, Londinium, that made quite a difference. – Karl Dec 21 '23 at 21:33
  • "Well, they do not grow much in water either." If it was "just water" there wouldn't be bacteria & molds. – stevea Dec 28 '23 at 11:08