For travelers who care about the freshness of the water itself, here's what makes free-flowing hot spring water special.
See Hakone private-onsen ryokan →What is free-flowing hot spring water?
Free-flowing hot spring water (gensen kakenagashi) means the source water is used without being recirculated or diluted, with fresh water constantly overflowing the tub. It's popular with hot-spring enthusiasts who want to experience the water's full mineral content and freshness (see also hot spring vs. reheated water).
Hakone ryokan with free-flowing water
Some ryokan run every single bath on their own free-flowing source. Aitayo tracks ryokan with free-flowing water at this list.
How to tell: check the changing-room notice
Under Japan's revised Hot Spring Act (2005), facilities are required to post a notice in the changing room (or similar area) disclosing whether the water is diluted, reheated, recirculated/filtered, or treated with a disinfectant. Rather than relying on the ryokan's marketing copy alone, checking this notice in person is the most reliable way to confirm whether a bath is genuinely free-flowing. Water constantly overflowing the rim of the tub is a rough visual cue, but some tubs are designed so the overflow isn't obvious — the posted notice is the more reliable source.
Free-flowing water can still be diluted or reheated
It's easy to assume “free-flowing” means the water is used completely untouched, but if the source water is too hot it may be diluted with cold water, and if it's too cool it may be reheated. The key distinction is whether the water is recirculated and reused — even with dilution or reheating, water that's used once and discarded still counts as free-flowing. If you want the strictest version, look for “100% gensen kakenagashi” (no dilution, no reheating) on the posted notice or in the ryokan's description.
FAQ
What is free-flowing hot spring water?
It means the source water is used without recirculating or diluting it, so fresh water is constantly overflowing the tub.
Which Hakone ryokan have free-flowing hot spring water?
Aitayo tracks them at /tag/kakenagashi.
Can free-flowing water still be diluted with cold water or reheated?
Yes — dilution or reheating can happen when the source water is too hot or too cool. As long as the water isn't recirculated and reused, it still counts as free-flowing. You can check the exact treatment on the notice posted in the changing room.
A ryokan is labeled “free-flowing” but the water isn't overflowing the tub. Is that a fake claim?
Not necessarily — Japan's National Consumer Affairs Center has logged similar complaints, though. Checking the changing-room notice, which discloses dilution, reheating, recirculation, and disinfection, is the reliable way to confirm the actual water treatment (see <a href='/en/onsen-keiji-guide'>how to read a hot spring notice</a>).
Last updated: 2026-07-17 ・ Reservations are on Rakuten Travel (Japanese site).