You’re not going to find a well defined germ theory breakdown of the potability of water because it did not exist. It’s not like they could identify clean water vs dirty water. It’s not like drinking dirty water meant you were going to die either. Generally speaking, people understood that drinking more alcoholic drinks was likely to have health benefits among other things, hence the term “water of life”. Drinking alcohol was seen as a move that would improve your health, including as literal medicine. It was frequently drank because it was good for you. Not strictly because they knew they couldn’t drink the water. They did drink a lot of dirty water too.