Explera DMC Japan chooses onsen for groups by the water as well as the building. Japanese rules require a bath to show whether its water is diluted, heated, recirculated or treated, and a new rating called Yuchelin now judges hot springs on the water alone. We read those notices before we book.
Yuchelin, a general incorporated association based in Tokyo, calls itself Japan's first hot spring rating guide. Its assessors visit each facility and judge the bath, not the rooms, food or service: the character of the spring, its freshness and rarity, how safely and hygienically it is managed, and its environmental and cultural value. Its first awards ceremony, Yuchelin Award 2026, was set for 26 October 2026, where the first three-star facilities are announced.
What does the notice at an onsen tell you?
Since 24 May 2005, Japan's Ministry of the Environment has required hot spring facilities to post a notice, with the reason, when they add water, heat the water, recirculate it through a filter, add bath additives or disinfect it. Look for these terms:
- Gensen kakenagashi. Spring water flows into the bath and out again without being recirculated.
- Junkan. The water is filtered and recirculated.
- Kasui and kaon. Water has been added, or the water has been heated.
None of these is a fault in itself. A spring that comes out of the ground too hot has to be cooled, and one that comes out cold has to be heated.
How do we use this when choosing onsen for groups?
- Large groups. Big hotels often recirculate and disinfect, which keeps a busy bath clean. For most clients, that is the right choice.
- Clients who care about the water. We look for smaller ryokan with free-flowing baths. They tend to have fewer rooms and smaller baths, so we split larger groups across nearby inns or bathing times.
- Sensitive skin and strong springs. Sulphur and acidic springs smell, sting or stain. We tell clients in advance and keep a milder option nearby.
For bathing rules, see our onsen etiquette guide and our tattoo guide. For premium stays, see our ryokan and onsen guide.
Sources: Ministry of the Environment notice on hot spring labelling (Japanese) and Yuchelin official site.
FAQ
What is Yuchelin? A hot spring rating guide from a Tokyo-based association. Its assessors judge the bath water itself, such as freshness, rarity and hygiene management, and give stars, starting with a first list of three-star facilities in October 2026.
What does gensen kakenagashi mean? It means spring water flows into the bath and out again without being filtered and recirculated. Many travellers prefer it, but it suits smaller baths best.
Is a recirculated onsen a bad choice for groups? No. Recirculation with filtering and disinfection keeps a busy bath clean, which is why large hotels use it. We match the bath to the group and the client's priorities.
Do onsen have to say how their water is treated? Yes. Since May 2005, facilities must post a notice, with the reason, if they add water, heat it, recirculate it, add bath additives or disinfect it.
Planning onsen stays for your clients? Write to b2b@explera.jp, message the trade desk on WhatsApp at +66 93 656 8090, or register on the B2B portal. Proposals within 24 hours. IATA TIDS 96215733, ASTA member 900408341.
