I think from ground water trace elements like lead are more likely. In my experience when I've been in places where groundwater was the household source via electronic pump, it's always been a case where you weren't supposed to drink it. And either had a reverse osmosis machine near by to use to fill bottles, or you just relied on store bought bottled water for drinking and cooking.
It would be interesting if in your cases it was high deuterium water though. It's not something I ever considered really.
Of course when straight groundwater is your best or only option, that's a hell of a lot better than having no source of plausibly safe water available. I've drank lake water where we would just disinfect it with a few drops of bleach for a couple of weeks when on trips. But was always told that this is a short term solution for convenience.