This isn't really a slam dunk debunking. I get that medieval people knew about good and bad water, and that they had other reasons to prefer small drinks. But it doesn't change the facts that:

- Medieval people DID drink constantly (mostly in the form of small drinks)

- SOME medieval didn't have access to consistently good water.

- Even good water supplies can be tainted

There are cases were it was noted that a disease would outbreak from the local water supply, but no one from the brewery next door would get sick. This was not lost on most people, so water was drunk but with some risks assumed.

And most notably, we still see this exact dichotomy today in the third world where dysentery and diarrea are still common causes of death. And people with the means or preference towards prepared drinks often fare better.