Well, obviously, medieval people understand that water is good, learn to bathe and smell good, which eventually lead to people discovering that Earth is round and they launch an Industrial Revolution. The End.
More seriously, bathing was quite common during Middle-Ages : allow me to translate something I made recently.
For instance, one of the reasons that made Charlemagne choose Aachen were the former baths (Aachen -> Acquae = Waters). We do know that thermal journeys existed during Middle-Ages, and not only in long romanized places but as well in England.
It doesn't mean great roman baths (that were more or less reserved to urban population and a certain elite) maintained themselves but similar practices did.
Mostly in smaller baths (as ervegetism was more focused on religious monuments and works), which are named étuves in french (stews in english, I think) you could find in palaces and important castles, but as well as on towns (private baths, but more usually public baths)
The latter were a common and organized trade with everything from poor and dirty bath with cold water to heated baths with massages and perfumes, and generally accompanied with an endemic prostitution. As medieval housing was quite limited, toilet was made outside : the list of mentions in pictural or litterary sources is really long : one baths because you need to be clean, because it's good for you, and because it makes you look good (especially with the medieval fetish on hair)
Of course, the usual "In my time...", there religious full of the idea that taking care of yourself was insanely egotist and prideful shouted.
Now, if religious men were listened at this time...Well, you don't take beauty advices from homless drunkyards? Medieval people didn't used to themselves.
Even within clergy, critics on a too sctrict ascetism existed largely, up to have religious sources representating bathings (such as Villefranche-de-Rouergue)
Without mentioning importance of water in religious practices, including popular ones, would it be only trough its relationship to baptism. Putting statues of saints in water, blessed water, miraculous springs (up to nowadays with Lourdes). Bishops themselves loved property and sensuality of a good bath.
Public baths eventually disappeared because of several factors:
- Epidemics and plague : how diseases are transmitted is unknown but it doesn't mean that people didn't make the relation between large gathering of people exchanging fluids and medical risks (mostly in fear porous skin let the disease enters), with water being suspicious.
- Immorality : most of them where just whorehouses, sort of a thai massage entreprise, at the point that "stew" meant bordello in English.
In a context of re-evangelisation and re-moralisation (largely due to the plague) it was bound to backfire.