Is tap water potable?

As subject, is tap water in Japan hotels potable?
Thanks in advance for your help.

Generally yes, unless there is a sign indicating otherwise. However, in some larger cities, such as Tokyo (at least the last time I tried many years ago), the water can sometimes taste badly due to chemicals put into the tap water. In the countryside, tap water is generally very delicious.

yes, it is potable. I did not notice a bad taste in Tokyo (nor elsewhere) but that is obviously personal taste. It is generally not potable in trains and planes.

As suggested, it's potable unless mentioned otherwise, but some people from overseas seem to feel slightly sick when they drink water they are not used to.

In any case, a local hotel guest would typically boil the tap water using the pot equipped in the room, or they would just drink the free 500 ml/day or so bottled water that's also usually offered in the room. I'm Japanese, and I don't even drink tap water at home here in Japan. I filter it.

Yes. From my experience, no different to the UK (sometimes better - my tap water here currently reeks from fluoridation). If you are concerned, mineral water is widely available from vending machines and konbinis.

Alternatively, you can take a bottle with a built-in filter, filling it from the tap, and use that - the filters are effective, but the seals never seem to work 100%, some water always dripping out when you use them - check the reviews before buying. They aren't cheap either, but I guess you could justify it as quake survival gear.

Japan does have an extensive market in household water filters, some of which cost serious money. Not because there is anything particularly wrong with the tap water. Gadgets like that are popular in Japan (as they are in the UK) and water filtration satisfies the cultural passion for cleanliness and purity.

I'd advise against taking a mouthful of water from the spiritual cleansing stations (temizuya) at the entrance to shrines. The ritual involves pouring water on each hand and then rinsing your mouth. Discreetly fake the last bit. Ingesting water from open, external sources isn't a good idea.

the free 500 ml/day or so bottled water that's also usually offered in the room

I don't recall ever having a free water bottle, and I do a fair bit of traveling. Maybe that's a thing posh hotels do...

I've kept record that at least Marriott Associa, official rate starting from 19,800 yen per room, offers free bottled water in their rooms. It doesn't mention anything on their website, but bottles are always there when I stay. You can buy similar bottles at convenience stores for about 100 yen anyway. Just for reference.

I'd never encountered tap water problems on any of my trips to Japan until I went with a friend years ago that reacted negatively for about a week (of a month long trip) until he acclimated. Then he told me this happens to him whenever he travels (even domestically in the US). The ironic thing is that he lives in a major US southern California city that has some of the most foul tasting tap water I've ever encountered.

I don't recall ever having a free water bottle, and I do a fair bit of traveling. Maybe that's a thing posh hotels do...

Not sure what your definition of a 'posh' hotel is Firas but a daily free bottle of water is very commonplace at nearly every hotel I've stayed at in Japan; even the cheap APA type of business hotels. If your traveling is only to hostels though, of course, YMMV.

Happy New Year to all! I just got back from Marriott Associa and realized that we get 2 free 500 ml bottles per guest per night. One is refrigerated and another in room temperature. Just trying to share my experience.