While growing up in a very dry region in India, I remember people get boring wells drilled in their land to extract ground water (sometimes even 1000 feet deep). This ground water often tastes subtly sweet and I remember drinking that water in summer heat, getting this amazing sweet after taste. In fact people go to neighbors who have "meetha pani" (sweet water) for their daily consumption. Not sure if that was D2O and not H2O.
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.
My understanding of the issue with pumped well water (at least where I am) is more that you don't know how long the water has been sitting in pipes or tanks. (Open wells - with a bucket - have different issues as they are open)
The wells here are typically 50m+ meters deep, so if you have a 1 inch connection that's more than 25 litres just sitting in the pipe. For longevity you don't want to run the pump every time you turn on the tap, so there's usually a pressurised tank with another 25L or so and a pressure controlled switch in the pump.
So if you want to get 'fresh' water you first need to run 50L through the system. There's also the issue of extra minerals - the water here has a lot of iron, which turns everything red unless you have a good filter. The filters will have a low flow rate, so you need another tank to store the filtered water. Much easier to just get a RO system or bottled water for drinking :-)
50m of earth is going to produce some of the cleanest water you've ever had, unless of course there is pollution from heavy industry nearby. I know a few people who collect water daily from springs and drink that as is. If you lookup DIY water purification systems they typically have one plastic tank filled with sand and another with charcoal which filters pretty much all of the stuff out you don't want to drink.
>Experiments with mice, rats, and dogs[42] have shown that a degree of 25% deuteration causes (sometimes irreversible) sterility, because neither gametes nor zygotes can develop. High concentrations of heavy water (90%) rapidly kill fish, tadpoles, flatworms, and Drosophila. The only known exception is the anhydrobiotic nematode Panagrolaimus superbus, which is able to survive and reproduce in 99.9% D2O.[40] Mammals (for example, rats) given heavy water to drink die after a week, at a time when their body water approaches about 50% deuteration.[43] The mode of death appears to be the same as that in cytotoxic poisoning (such as chemotherapy) or in acute radiation syndrome (though deuterium is not radioactive)
They used lead vessels to make wine taste sweeter as well. Saying that makes me curious as to what it would actually taste like. Stevia extract and aspartame are sweet but don't taste the same and both different from suger, what is lead like? The second thing that makes me wonder is, do I already know since I live in a city with some lead contamination in the tap water.
Didn't the Romans actually end up making red wine vinegar in the lead pots (letting the wine go bad), and the acetic acid reacted with the lead to form lead acetate (a.k.a. "sugar of lead")?
