Onsen OniOnsen Oni

Onsen chemistry extremes

Onsen at the extremes

The most striking springs in the catalog, by the numbers on their certificates.

Hottest sources

Temperature at the wellhead.

  1. 1Tocen GoshobohHyogo · Chloride100.5°C
  2. 2Tamatebako Open-air OnsenKagoshima · Chloride100.4°C
  3. 3Oedoonsen Monogata MasuyaMiyagi · Chloride100.0°C
  4. 4Shiraitonotaki OnsenOita · Sulfur100.0°C
  5. 5KamioboHyogo · Chloride99.4°C
  6. 6Kin no Yu hot springHyogo · Chloride99.4°C
  7. 7Odoriko Onsen KaikanShizuoka · Chloride99.3°C
  8. 8Ooedo Onsen Monogatari KounkakuMiyagi · Sulfate98.8°C
  9. 9Kō Sansō KanoHyogo · Chloride98.6°C
  10. 10Grandvrio HotelToyama · Simple98.3°C
  11. 11Teruyu OnsenOita · Simple98.1°C
  12. 12Arima Hot Spring Ryokan HanamusubiHyogo · Chloride98.1°C

Most acidic

Lowest pH, into battery-acid territory.

  1. 1Sainokawara RotenburoGunma · Acidic1.70pH
  2. 2Tsukahara Onsen Kakono IzumiOita · Sulfate2.00pH
  3. 3Susukinohara IchinoyuKanagawa · Acidic2.00pH
  4. 4SenkyoroKanagawa · Acidic2.10pH
  5. 5Hakone Onsen Sanso NakamuraKanagawa · Acidic2.10pH
  6. 6Mount View HakoneKanagawa · Sulfate2.10pH
  7. 7Shinanoki IchinoyuKanagawa · Sulfate2.10pH
  8. 8YamadayaKanagawa · Sulfate2.10pH
  9. 9Ryokan MasuyaKanagawa · Acidic2.10pH
  10. 10Kokuminshukusha HakonetaiyosansoKanagawa · Sulfate2.10pH
  11. 11Re Cove HakoneKanagawa · Acidic2.10pH
  12. 12Onsen Hotel GorakanKanagawa · Sulfate2.20pH

Most alkaline

Highest pH, the silky beautifying waters.

  1. 1Tenkei Izumi Shirane TōGen Ten Emi 閣Yamanashi · Simple10.40pH
  2. 2Yamato Temmokuzan OnsenYamanashi · Simple10.20pH
  3. 3Nanki Susami Onsen Hotel BellvedereWakayama · Sulfur10.10pH
  4. 4Ryokan ShirasagiWakayama · Sulfur10.10pH
  5. 5Rivage Spa HikigawaWakayama · Simple10.10pH
  6. 6Enzan Onsen KouchisouYamanashi · Sulfur10.10pH
  7. 7Hotel Mount FujiYamanashi · Simple10.00pH
  8. 8Tsutsumigawa Hot SpringYamanashi · Simple10.00pH
  9. 9Shin Inago Gawa Onsen Yū･TorioShizuoka · Chloride10.00pH
  10. 10Yamanakako Onsen Benifuji no Yu hot springYamanashi · Simple10.00pH
  11. 11Hakushū Shiozawa Onsen Fossa･Maguna No YuYamanashi · Chloride10.00pH
  12. 12Kō Raku No YuFukuoka · Sulfur9.98pH

Strongest brine

Most dissolved solids.

  1. 1Kō Sansō KanoHyogo · Chloride44.0g/kg
  2. 2Tocen GoshobohHyogo · Chloride37.6g/kg
  3. 3Fukuro no YuWakayama · Iron-bearing36.9g/kg
  4. 4KamioboHyogo · Chloride36.1g/kg
  5. 5Kin no Yu hot springHyogo · Chloride36.1g/kg
  6. 6Tamatebako Open-air OnsenKagoshima · Chloride34.2g/kg
  7. 7Kinokuni OnsenWakayama · Chloride32.2g/kg
  8. 8Izumi Tenku no Yu Ariake GardenTokyo · Iodine-bearing29.8g/kg
  9. 9Century Marina HakodateHokkaido · Chloride27.6g/kg
  10. 10Arima GyoenHyogo · Chloride26.1g/kg
  11. 11Ojiro No YuYamanashi · Chloride25.5g/kg
  12. 12Suruga Health LandShizuoka · Chloride24.8g/kg

Most carbonated

Free CO₂, the fizz on your skin.

  1. 1Hanayama Onsen Yakushi No YuWakayama · Chloride2,631mg/kg
  2. 2Lamune OnsenOita · Bicarbonate1,400mg/kg
  3. 3Hanairo Hot SpringOita · Carbonated1,130mg/kg
  4. 4Katsuragionsen HappunoyuWakayama · Carbonated1,094mg/kg
  5. 5Shichirida Onsen Konoha-no YuOita · Carbonated1,010mg/kg
  6. 6Gin no Yu hot springHyogo · Carbonated1,010mg/kg
  7. 7Sui Jin NomoriOita · Iron-bearing989mg/kg
  8. 8Kawa No Eki Sen Koya Koi Bo Taru Onsen KanFukuoka · Bicarbonate921mg/kg
  9. 9Negiya RyofukakuHyogo · Iron-bearing834mg/kg
  10. 10Arima Hot Spring Ryokan HanamusubiHyogo · Chloride755mg/kg
  11. 11Shinseikan ryokan Ukenokuchi onsenOita · Bicarbonate750mg/kg
  12. 12Hotel New AraoMiyagi · Bicarbonate706mg/kg

Highest radon

Radioactive springs studied for joint pain.

  1. 1Arima Hot Spring Ryokan HanamusubiHyogo · Radon2,240Bq/kg
  2. 2KokiHyogo · Radon1,900Bq/kg
  3. 3Gin no Yu hot springHyogo · Radon1,060Bq/kg
  4. 4Arima GyoenHyogo · Radon554Bq/kg
  5. 5Chomei-ji Onsen - Amahanoyu Hot SpringShiga · Radon330Bq/kg
  6. 6Torikai RyokanTottori · Radon274Bq/kg
  7. 7ShikimatsuriOsaka · Radon237Bq/kg
  8. 8Matsuba Onsen Taki-no-yuOsaka · Radon237Bq/kg
  9. 9Tō Shō KaSaga · Radon221Bq/kg
  10. 10Hotel YunomotoMie · Radon159Bq/kg
  11. 11Humor Resort Taisanji Nadeshiko-no-yu Hot SpringHyogo · Radon144Bq/kg
  12. 12Sakura-yu - Yamaga Onsen MotoyuKumamoto · Radon141Bq/kg

Most silica

Metasilicic acid, a natural moisturizer.

  1. 1Maeda onsenOita · Chloride685mg/kg
  2. 2NetsunoyuOita · Chloride685mg/kg
  3. 3Tamatebako Open-air OnsenKagoshima · Chloride588mg/kg
  4. 4Oniishi No YuOita · Chloride584mg/kg
  5. 5ShouninyuOita · Chloride566mg/kg
  6. 6Sainokawara RotenburoGunma · Acidic528mg/kg
  7. 7Jigokubaru OnsenOita · Chloride515mg/kg
  8. 8Yumotoya RyokanOita · Acidic396mg/kg
  9. 9YumetamatebakoOita · Chloride387mg/kg
  10. 10TaninoyuOita · Chloride358mg/kg
  11. 11Ooedo Onsen Monogatari KounkakuMiyagi · Sulfate355mg/kg
  12. 12KurokawasoKumamoto · Bicarbonate348mg/kg