Once when I visited Latvia, I "hardened" my system slightly by deliberately drinking the tanked water in my flat (odd theories I had then).
Out there I was drinking water out of the taps (not always recommended by the locals) and well water (slightly brown but quite smooth and pleasant).
No problems. Mind you - the country is highly underpopulated and farming less intense than here - so the chances of well water being polluted by weedkiller from the next field, or a cess pit built next to the well was pretty small. Even the Daugava River looked practically drinkable[1] - well I got the odd mouthfull swimming. Still alive.
Timbo
[1] That was 1997 - wouldn't want to do that a few years before when Belarus accidently dropped 128 tons of cyanide compounds in it!