国分5号
Kokubu No. 5Operated by · 岩戸温泉（一般公衆浴場）
曹
Bicarbonate
- Color
- colorless and transparent
- Taste
- tasteless
- Odor
- odorless
Sodium Bicarbonate spring
pH 7.9Weakly alkalineHot source · 55°CHigh silica
Composition fingerprint1.6 g/kg dissolved · Hypotonic
Na⁺93
HCO₃⁻83
Cl⁻16
◀ CationsAnions ▶
- Sodium Na⁺
- salt's cation — pairs with chloride to make the water salty.
- Bicarbonate HCO₃⁻
- "soda" — softens skin, leaves it smooth.
Known good for
- Smooth skindry, rough skin
- Aches & jointsstiff shoulders
- Recoveryfatigue, stress
A sodium-led bicarbonate spring of the classic jūsō-sen style, rising at a hot 55.2 °C in Kirishima. Weakly alkaline (pH 7.9) and soft on the skin, it sits squarely in Japan's beauty-water family. A generous 207.9 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother after a soak.
Sampled at wellhead·Analyzed May 21, 2019·株式会社東洋環境分析センター·Cert no. 鹿児島県第4号