Not really true.
They knew how to dig wells both deep and not so deep.
The water was very drinkable
As well alcoholic wine does not purify water.
I suppose it depended on where you live. I hear they used to throw the waste from buckets (think chamber pot style waste) in the streets in Rome. But I have also seen excavations of Greek or Roman toilets over rivers. If there were toilets over the tiber, Rome could have had some rather unhealthy water, but they did pipe water in from distant springs, probably polluted slightly from the lead used in the construction of the top of the aqueduct. But what about cities of 20 or 50k people that did not have aqueducts, or some village downstream from another village that did not bury its waste. Digging a well was a big deal. We even read about the patriarchs digging wells. It must have been a really big deal for them.
I don't remember the site, but I have read online that wine mixed with water can kill germs after about 24 hours. There might be something to the idea that alcohol served the purpose of purifying wine. It seems more likely to me that that was what they wanted to drink. A little wine in the water probably tasted better than just water to them. It gave them something to drink with meals. It also served as a way for poor farmers to preserve calories produced by the grapes. We might take calories for granted, but that was probably important for their health.
I read a theory that Europeans in the middle ages may have come to drink beer and wine because water tended to be dirty. The article argued that they may have drunk large amounts since childhood, making them a bit sluggish. But when coffee came from Africa, it stimulated their brains. It was also safe to drink because they boiled it. If they didn't realize boiling was the key, they probably weren't getting sick off of it. Instead of beer, they were drinking a mild stimulant, which stimulated their thinking about art, politics, science, etc. That was just a theoretical explanation.
As Christians we should not drink wine or beer to excess. I was raised hearing preaching against alcohol. I don't 'drink socially' or drink for pleasure. We have some wine in the house used for cooking. Heat causes alcohol to evaporate. I have had a little bit of an alcoholic beverage when I ate something strange, for example taking a couple of bites of a chicken sandwich at KFC in Jakarta and seeing it was raw. I drank part of a Bintang after that, hoping it might kill something. I'll take wine in communion.
But I also realize it was wrong of me to look at someone drinking one beer with dinner and think they were sinning. Drinking alcohol 'became a sin' over the years in certain types of churches. Methodist preaching against distilled liquors turned into preaching against beer and wine. And there was a big hubbub over some churches moving to grape juice after Baptist deacon Welch's invented a new method for preserving fresh unfermented grape juice in the early 1900s.