A term without a legal definition
"Gensen kakenagashi" is not a legal term. It generally means water piped from the source flows continuously into the tub and the overflow is discarded rather than recirculated. The water in the tub is constantly renewed, keeping it fresh and often making disinfection unnecessary.
Since the 2005 amendment of the Hot Spring Act, facilities must post whether water is added, heated, recirculated/filtered, treated with additives or disinfected. "No recirculation" on that notice is the main sign of a free-flowing bath. The Japan Spa Association also runs a "natural onsen signboard" scheme that grades five items — source condition, added water, heating, flow, fresh-water inflow and disinfection — on a five-point scale.
Why it is hard: flow and temperature
Free-flowing needs enough water for the size of the tub — as a guide, enough to replace the bath's volume every few hours. A large bathhouse in a place with little flow has no choice but to recirculate.
Temperature is the other problem. A 90 °C source cannot be used as it is; it must be cooled. Adding cold water is easy but dilutes the minerals, so Kusatsu uses "yumomi" (stirring with boards) and "jikan-yu" (timed bathing), and at the Yubatake it runs the water along wooden channels to cool in the air. Takayu keeps a long run from source to tub to cool naturally, and every facility there is free-flowing. Conversely a 38 °C source may be too cool for winter without heating.
So "no added water, no heating, no recirculation" all at once is achieved only by fortunate springs with abundant flow at just the right temperature.
Aspere · CC0
Kusatsu Onsen
草津温泉
Gunma · 100 Onsen to Know Japan — No. 25
Thirty-two thousand litres a minute of pH 2.1 acid water rise in the middle of town and cool as they run down wooden channels.
Purplepumpkins · CC BY-SA 3.0
Takayu Onsen
高湯温泉
Fukushima · 100 Onsen to Know Japan — No. 22
Nine sources, 2,589 litres a minute, and not a drop of tap water or a single boiler: the milky water is cooled only by gravity on its way down the hill.
Myōken Onsen
妙見温泉
Kagoshima · 100 Onsen to Know Japan — No. 98
A riverside toji village on the Amori River where every inn has its own spring and not a single bath is recirculated.
Is recirculation bad?
Recirculation with filtration is how a limited supply serves many bathers: water passes through a filter, is reheated and returned to the tub. To prevent Legionella, regulations then require chlorine-based disinfection. The smell of disinfectant and changes in the water (a sulfur spring losing its cloudiness, for instance) are its drawbacks.
Many systems are "semi-recirculating", adding some fresh water, and it can differ bath by bath — "open-air bath free-flowing, indoor bath recirculated" is common within one facility. That is why this atlas records each bath separately.
"100% source water" is not the same thing
"100% source water" means no water is added; it says nothing about recirculation. "Natural onsen" means the water is a legal onsen; it is unrelated to whether the bath is free-flowing. A bath labelled "kakenagashi" may still be heated.
The reliable check is the changing-room notice: what it says about added water, heating, recirculation and disinfection. In this atlas's articles, we record "yes/no" only for items we could read on an official site or notice; everything else remains "unconfirmed".
Places that declared themselves free-flowing
Some onsen towns have declared that every facility is free-flowing. Takayu (Fukushima) made a "kakenagashi declaration" in 2010; Totsukawa (Nara) is said to have been the first in Japan to do so, in 2004; and Myoken (Kagoshima) also advertises all-facility free flow. Such declarations are evidence of generous water.
In the search, "has a free-flowing bath" lists only areas where this was confirmed bath by bath in an in-depth article.
Purplepumpkins · CC BY-SA 3.0
Takayu Onsen
高湯温泉
Fukushima · 100 Onsen to Know Japan — No. 22
Nine sources, 2,589 litres a minute, and not a drop of tap water or a single boiler: the milky water is cooled only by gravity on its way down the hill.
Soica2001 (talk) · Public domain
Totsukawa Onsen
十津川温泉
Nara · 100 Onsen to Know Japan — No. 69
Every bath in the village runs straight from the source, with no recirculation, no dilution and no chlorine. This is the heart of the mountain spa district that made that pledge in 2004.
Myōken Onsen
妙見温泉
Kagoshima · 100 Onsen to Know Japan — No. 98
A riverside toji village on the Amori River where every inn has its own spring and not a single bath is recirculated.
Glossary
- Recirculation / filtration
- Passing bath water through a filter, reheating it and returning it to the tub. Requires disinfection.
- Yumomi
- At Kusatsu, stirring the water with long boards to cool it without adding cold water.
- Natural onsen signboard
- Japan Spa Association scheme grading source condition, added water, heating, flow and disinfection on five levels.
Related onsen
Purplepumpkins · CC BY-SA 3.0
Takayu Onsen
高湯温泉
Fukushima · 100 Onsen to Know Japan — No. 22
Nine sources, 2,589 litres a minute, and not a drop of tap water or a single boiler: the milky water is cooled only by gravity on its way down the hill.
Soica2001 (talk) · Public domain
Totsukawa Onsen
十津川温泉
Nara · 100 Onsen to Know Japan — No. 69
Every bath in the village runs straight from the source, with no recirculation, no dilution and no chlorine. This is the heart of the mountain spa district that made that pledge in 2004.
Myōken Onsen
妙見温泉
Kagoshima · 100 Onsen to Know Japan — No. 98
A riverside toji village on the Amori River where every inn has its own spring and not a single bath is recirculated.
Aspere · CC0
Kusatsu Onsen
草津温泉
Gunma · 100 Onsen to Know Japan — No. 25
Thirty-two thousand litres a minute of pH 2.1 acid water rise in the middle of town and cool as they run down wooden channels.