In the last country, I was staying in the older parts of the cities. On the last peregrination through the Balkans, I invariably purchased the large jugs of water, rather than using the taps (generally, this is considered the way to go, as the jugs of water are very inexpensive, and the taps are risky). But in the old parts of the cities in that country (where I've not stayed before when I've visited that country), large jugs of water generally aren't available in the stores. Realizing this, I confirmed with the folks handling the rental that they considered the water safe, and that they and their families used it. After trying it for the month and a fortnight or so, I'm fairly sure that the folks there have habituated themselves to bad water, and would be much better off if the stores (like the stores in the old cities in the country to the east) would stock the large bottles of water. After running, I would be thirsty for the orange and the milk, but except on the warmest mornings, I wasn't at all thirsty for the water from the taps. And it might have weakened me a bit -- I felt that after this most recent journey.
Nothing catastrophic, I'm sure that switching back to the large jugs now will wash all of the bad stuff away, but it was a good lesson in the need to keep to the inner discipline, even when the ways of the place are at some variance.