People can grow vegetables and simply eat. But bread is way too complicated.
There is a bakers’ dozen of big steps to go from wheat into bread. And multiple special structures needed too.
Same with beer. Wine makes total sense but how do you even invent ale? How are these common foods everyone knows and uses?
I was thinking “imagine if mediveal people knew how to boil seawater and sell salt” and now I spent 20 extra minutes in the shower.
To be fair, wells and aquaducts are fairly clean ways to get water (read: animals haven’t shit or died in it yet). Rivers and other surface water were as bad as today, if not worse because it was a de facto village sewage system. Water quality issues were also mitigated by a diet very heavy in stews and soups, so less extra hydration was needed.
Why do you think that shit was put into the waters. There were no artificial fertilizers. Dung (animal and human) was an important resource you wouldn’t want to waste. Till quite recently it was normal to collect your waste in the cesspool and than fertilize your fields with it or sell it to an farmer