If this question is completely inaccurate historically, please answer it in a way that’ll enlighten me.
If this question is completely inaccurate historically, please answer it in a way that’ll enlighten me.
Ah! Hail, OP, for this is exactly the thing that got me into history, and is the myth that it is my life's work to kill. Put plainly, the notion that pre-modern people all drank alcoholic drinks to make water safe is pop-cultural nonsense.
I shall direct you first to the VFAQ (Middle Ages, subsection Health and Hygiene, in case your browser doesn't go there immediately), in particular the answers from u/sunagainstgold and u/Qweniden.
To illustrate just how Serious Business water was for the Medieval era, more u/sunagainstgold on the incidents she touches on in her VFAQ post:
Of course, none of this is to say that the people of the Medieval period avoided alcohol. Quite the opposite; booze in its multifarious forms is a definite fixture in the Medieval liquid diet. No; Medieval people drank alcohol because water is boring. (In fact, this remains true today, and with drinks beyond just booze. Look me in the eye and tell me seriously that, in the past three days, you have drank only water and no other beverage at all. No tea, no coffee, no booze, no soda, no sports drink, only water. If you can honestly say that, then I commend you for being a most rare individual. And if you'd ask me, I'd say the whole paragraph above applies to all people of all places and times - but I hang around with the Medievalists and not the other eras, so Medieval it is. But I will still defend that water is boring and people find ways around that.)
u/sunagainstgold has in the FAQ and the first linked answer called water 'the beggar's drink', and it's exactly that societal attitude that drives the nominal Medieval disdain for drinking water. The Medievals did drink water - but if they could at all help it, not straight water. Do that, and you're a poor person who can't Do Things to your water to elevate it. When we see elites drinking water, they've all Done Things to it. Liutprand of Cremona admired the water drank by the Byzantine emperor Constantine VII, for it had been boiled, then frozen. Other elites improved their water by Adding Things, such as ice, wine, parsley seed, vinegar, honey, fruit, and so on.
Which takes us to alcohol and the Medievals. Remember, the water is safe, or safe enough - but it's still common, so it has to be elevated to make it fit for consumption by people of worth. Alcohol has to be made, not just collected. Someone has to put effort into turning the ingredients into a drinkable product, and then the drinker then has to shell out money to purchase said drinkable product. When you need to display your status and your wealth, it's easy to see where alcohol meets that need.
But if you're asking me, it's because water is boring and people anytime anywhere will do anything they can to drink anything but water. Even if they have to admit that they'll have to drink water sooner or later.
Adding on to the copypaste that is the above: Yes, they'd have used water. Indeed, the Medievals knew very well how to judge water, with clarity being an important factor as to whether that water would be judged fit for consumption, or only for other uses. The Medievals understood quite well that purity is relative to task; water that is good for washing dishes is not necessarily usable for cooking food with or drinking.
In addition to what u/DanKensington wrote, note that a common and effective method of making water safe is to boil it. Most unsafe water is unsafe due to bacteria, viruses, or parasites. Generally, harmful bacteria etc. are killed by boiling. When water is used to cook soup and stew, it is hot enough to break down proteins etc. in the food, and therefore also hot enough to break down proteins in any bacteria, viruses, and parasites, killing them.
Unpleasant though it might sound, it would usually be quite safe to make soup or stew using stinking swamp water.
Flooding often resulted in many deaths due to water-borne illnesses, and still kills people today through such diseases. This is partly because safer sources of water - wells and clean rivers - are covered by floodwaters that include a mix of sewerage, garbage, and dead animals. However, one factor that makes this much worse is that flooding can also mean a shortage of usable firewood or other fuels for boiling water (and even today, flooding often results in a failure of electricity supply) - no clean water is available, and the unclean water that is available can't be boiled.