Singapore is (I think) the only country in Asia that you can drink water from a tap. But even so, people here still boil water before drinking it.
So outside people will buy water even if a fountain was available.
So outside people will buy water even if a fountain was available.
Of course everyone still boils their water...
[0] https://www.wsd.gov.hk/en/core-businesses/water-quality/buil...
I've never been to South Korea, yet.
I've traveled all over Japan including those places and others far more rural and never seen that, it sounds really strange. Are you sure it didn't say you can drink the tap water? Maybe in broken Engrish?
Only places I've seen in Japan with warnings against drinking tap water is on trains and porta-potties.
You probably misunderstood, or perhaps the hotel staff were all sharing the same oddly wrong english handbook...
And perhaps suggested you buy some bottled instead?