Q & A
Frequently Asked Questions
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Is water below 25°C still an onsen?
Why is the bath temperature different from the sheet?
The four temperature bands
Under Japan's Hot Spring Act, water that is 25°C or warmer when it emerges counts as an onsen regardless of its minerals. The band also appears in brackets in the spring type name (e.g. "Chloride spring (isotonic, neutral, hot)").
| Band | Temperature at source | When used in a bath |
|---|---|---|
| Cold mineral spring | below 25°C | Almost always heated |
| Low-temperature spring | 25 to below 34°C | Often heated; some baths offer it lukewarm |
| Warm spring | 34 to below 42°C | Close to a bathable temperature |
| Hot spring | 42°C and above | Often cooled with added water, stirring or heat exchange |
Source temperature is not bath temperature
The temperature on the sheet is measured where the water emerges. Hot sources are cooled by adding water or letting them cool naturally; cold and low-temperature sources are heated with a boiler before reaching the bath. Whether water is heated or diluted is shown on the "usage" notice posted at the bath.
- If water is added to cool a hot source, the minerals are diluted
- Heating alone, without added water, does not change mineral concentration
- Bath temperature varies by facility and season
Find onsen by temperature
On Explore, use "Sort by component" to order onsen by the spring temperature on their analysis sheets.
Onsen towns are often rural with patchy Wi-Fi and limited public transport. Sort out data, tours and a car before you go.
- Japan eSIMAiralo
- Japan eSIMYesim
- Tours, passes & transfersGetYourGuide
- Tours, passes & transfersKKday
- Car rentalDiscover Cars
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