Japan
Definition
Hot Spring Act (1948): 25 °C or above, or one of 19 substances above a threshold. "Therapeutic springs" with spring-type names meet a stricter standard.
Geology & heat
On the Pacific Ring of Fire. Volcanic acidic and sulfur springs coexist with non-volcanic chloride and moor springs from deep drilling.
Naked or swimsuit
Naked, segregated by sex. Swimsuits are generally not allowed; mixed bathing survives in places, increasingly with lent bathing garments.
Bathhouse, pool or spa
Inn baths, communal bathhouses, day-use baths. Thermal pools are rare; foot baths are common in towns.
Therapy, rest or leisure
Toji survives, but the mainstream is one- or two-night rest and tourism. Short soaks in hot water around 42 °C.
Link to lodging
Bath and inn are one product: the "onsen ryokan" bundles lodging, meals and bathing. Many places also admit day visitors.
Food, towns, local culture
Onsen towns walked in yukata; food cooked with the spring's heat; links with literature and Edo-period rankings.
Drinking cures
Drinking fountains exist at some springs but are less common than in Europe; require a licence and posted dosage.
Pricing
Communal baths ¥100–500, day-use baths ¥500–2,000, inns mostly ¥10,000–50,000 with two meals. A bathing tax (typically ¥150 per night) is added.
Iceland
Definition
No legal definition like Japan's; geothermal pools and natural pools are loosely called hot springs or geothermal pools.
Geology & heat
Sits on the Mid-Atlantic Ridge. Around nine-tenths of homes are geothermally heated; some pools (Blue Lagoon) use water from a geothermal power plant.
Naked or swimsuit
Swimsuits. But a thorough naked shower in the changing room before entering is strictly expected.
Bathhouse, pool or spa
Every town's public geothermal pool (sundlaug) is a centre of daily life; tourist lagoon spas and wild natural pools (the Reykjadalur river) exist alongside.
Therapy, rest or leisure
Everyday socialising and leisure; chatting with neighbours in the hot tub (heitur pottur). Therapy is a minor purpose.
Link to lodging
Lodging and bathing are usually separate; pools are municipal. Some lagoon spas have attached hotels.
Food, towns, local culture
The pool is the town square; Reykjavik's municipal pools fill with commuters before work.
Drinking cures
Little tradition of drinking cures.
Pricing
Municipal pools about ISK 1,000–1,500 for adults; lagoon spas range from a few thousand yen to well over ¥10,000.
Taiwan
Definition
A Hot Spring Act (2003) defines springs by 30 °C or a mineral standard, with a certification mark for licensed facilities.
Geology & heat
Same volcanic belt as Japan. Beitou (sulfurous, acidic, source of hokutolite), Yangmingshan, Zhiben, Jiaoxi. Onsen culture arrived under Japanese rule.
Naked or swimsuit
Two styles side by side: Japanese-style naked, sex-segregated public pools and swimsuit outdoor thermal pools. Private rooms (tang-wu) are very common.
Bathhouse, pool or spa
Private rooms in hot-spring hotels, public baths, resorts. Beitou's Japanese-era public bathhouse is now the Beitou Hot Spring Museum.
Therapy, rest or leisure
Leisure, often couples and families in private rooms. A winter pastime.
Link to lodging
Many hot-spring hotels with in-room baths; day-use private rooms for one or two hours are common.
Food, towns, local culture
Hot-spring eggs, night markets in spring towns, Jiaoxi's spring-fed vegetables. Beitou is reachable by metro from central Taipei.
Drinking cures
Not common.
Pricing
Public baths from tens to a few hundred NT$; private rooms about NT$500–2,000 per hour.
New Zealand
Definition
No legal definition; facilities using geothermal water are called hot pools or thermal pools.
Geology & heat
The Taupō Volcanic Zone on the North Island (Rotorua, Taupō), long used by Māori for cooking and bathing. Hanmer Springs on the South Island is non-volcanic.
Naked or swimsuit
Swimsuits, required in public pools.
Bathhouse, pool or spa
Complexes with several pools at different temperatures, private pools, and wild springs in rivers and on beaches (Kerosene Creek, Hot Water Beach).
Therapy, rest or leisure
Leisure and family outings. Rotorua has a spa-resort history (the 1908 Bath House).
Link to lodging
Lodging and bathing are mostly separate; some motels have their own thermal pools.
Food, towns, local culture
Māori hāngī cooked with geothermal steam; Rotorua, the town that smells of sulfur.
Drinking cures
Little tradition of drinking cures.
Pricing
Public thermal pools about NZ$20–40; private pools cost extra.
Hungary
Definition
Groundwater above 30 °C is thermal water (termálvíz); water with recognised medical effects is certified as medicinal water (gyógyvíz).
Geology & heat
Not volcanic: deep groundwater in the thin-crusted Carpathian Basin. Budapest alone has over a hundred sources.
Naked or swimsuit
Swimsuits. Some baths (Rudas) once had naked single-sex days; most are now mixed with swimwear.
Bathhouse, pool or spa
Ottoman-era domed baths (Rudas, Király), palatial 19th–20th-century spas (Széchenyi, Gellért), provincial thermal pools.
Therapy, rest or leisure
Balneotherapy is a medical treatment covered by social insurance; also leisure (chess in Széchenyi's pools).
Link to lodging
Lodging and baths are separate; at resorts such as Hévíz, spa hotels have doctors on staff.
Food, towns, local culture
The baths are social spaces — Budapest even hosts pool parties.
Drinking cures
A drinking-cure tradition (Budapest's drinking halls, a large mineral-water industry).
Pricing
Budapest's major baths about HUF 8,000–12,000 for a day ticket; cheaper in the provinces.
Italy
Definition
Terme since Roman times. Mineral waters with recognised therapeutic effect are certified by the Ministry of Health, and spa therapy can be prescribed.
Geology & heat
Diverse: volcanic (around Naples, Ischia, Sicily) and the travertine springs of Tuscany (Saturnia).
Naked or swimsuit
Swimsuits, required in public terme.
Bathhouse, pool or spa
Medical terme (mud therapy, inhalations), hotel thermal pools, free natural springs (the Saturnia cascades, the channels of Bagno Vignoni).
Therapy, rest or leisure
Therapy (one annual spa course under national insurance) and wellness leisure.
Link to lodging
Many spa hotels, but village springs are separate from lodging.
Food, towns, local culture
The memory of Roman baths; food and wine in Tuscany's spa villages.
Drinking cures
A strong drinking-cure tradition (Montecatini, Fiuggi).
Pricing
Natural springs free to a few euros; terme about €20–60.
Germany
Definition
Springs above 20 °C are Thermalquellen; waters meeting mineral criteria are certified Heilquellen by the state. Towns titled "Bad" are certified health resorts.
Geology & heat
Few volcanoes; mostly deep groundwater. Baden-Baden, Aachen and Wiesbaden have been spas since Roman times.
Naked or swimsuit
Two cultures: sauna areas are naked and mixed; pool areas require swimsuits. Baden-Baden's Friedrichsbad is naked throughout.
Bathhouse, pool or spa
Thermen (large thermal pool complexes), Kurhäuser, sauna complexes.
Therapy, rest or leisure
The Kur tradition: multi-week stays on a doctor's prescription, partly covered by insurance.
Link to lodging
Lodging and baths are separate; spa towns pair therapeutic hotels with public Thermen.
Food, towns, local culture
Walks in the Kurpark, spa concerts.
Drinking cures
A strong drinking tradition, with Trinkhallen (drinking halls).
Pricing
Thermen about €15–35 for two to four hours.
Türkiye
Definition
Thermal springs (kaplıca) and mineral waters are certified by the Ministry of Health, with standards for therapeutic facilities.
Geology & heat
A tectonically active country with very many springs. Pamukkale's travertine terraces are a World Heritage Site.
Naked or swimsuit
Swimsuits. In the hamam, a waist cloth is worn and sexes are separated.
Bathhouse, pool or spa
Spa-hotel pools, public kaplıca, hamams. Pamukkale's "Cleopatra's Pool" lies among ancient ruins.
Therapy, rest or leisure
Largely therapeutic (rheumatism and so on), with families staying for long periods.
Link to lodging
Staying at a thermal hotel for a course of treatment is common.
Food, towns, local culture
The scrub and foam wash of the hamam; family trips to spa towns.
Drinking cures
Drinking mineral water is common.
Pricing
Public kaplıca are inexpensive; at thermal hotels bathing is usually included in the room rate.
United States
Definition
No single federal definition. The USGS defines a thermal spring as one warmer than the local mean air temperature; regulation is by state.
Geology & heat
Concentrated in the volcanic and tectonic West (Yellowstone, California, Colorado, Idaho). Yellowstone's thermal features are off-limits to bathing.
Naked or swimsuit
Swimsuits are the norm; some wild and private springs are clothing-optional.
Bathhouse, pool or spa
Resort thermal pools (Glenwood Springs), wellness spas (Esalen), wild springs on public land.
Therapy, rest or leisure
Leisure and wellness; a 19th-century history as health resorts (Hot Springs National Park).
Link to lodging
Integrated at resorts; wild springs have no lodging.
Food, towns, local culture
Springs sacred to Native peoples; spa towns of the frontier era.
Drinking cures
Rare, with historic exceptions such as Saratoga Springs.
Pricing
Resorts US$20–80; wild springs free to a few dollars.
Where we compare numbers of hot springs, we show the source, survey year, scope and definition side by side. Figures that are not comparable are not presented as a world ranking.
