For the purposes of this question, I’m talking medieval Europe. I know rivers in cities are typically quite polluted and not drinkable. Did most households have wells? I imagine this may be the case in the country but it seems impractical in the city.
I know this is a bizarre question, but I was randomly curious- I get headaches and muscle cramps if i have just a little bit less water than i’m used to, which on a given day is around 5 glasses. With limited access to clean water I doubt the average medieval european was able to match that. Do we have any evidence discussing historic hydration?
Oh no! Not the Medieval Water Myth! You'll rouse the ire of /u/DanKensington! You can read their extensive and excellent post on Medieval water supplies here.
The extent to which your Medieval urban water is drinkable really depends on the size of the city and where on a river it is. The idea that all urban waterways are intensely polluted and thus always have been is largely a result of 19th century teleological history, which saw the huge volumes of industrial pollution being dumped into urban waterways and assumed this must have always been the case. However, as DanKensington writes, wells and public fountains were extremely common in most medieval urban settings.
FWIW, I'm not surprised that you get cramps or headaches if you drink fewer than 5 glasses of water. That's already below recommended levels which suggest you need 6-8 glasses of water's worth of fluid intake a day.