三原山温泉 5号井
Miharayama Onsen Well No. 5Operated by · 東汽観光株式会社
湯
Simple
- Color
- colorless and clear
- Taste
- slightly bitter
- Odor
- odorless
Calcium-Sodium Bicarbonate spring
pH 6.9NeutralHot source · 84°CHigh silica
Composition fingerprint0.8 g/kg dissolved · Hypotonic
Ca²⁺44
Na⁺29
Mg²⁺20
HCO₃⁻70
Cl⁻17
◀ CationsAnions ▶
- Calcium Ca²⁺
- settling and calming; can leave a white mineral bloom.
- Bicarbonate HCO₃⁻
- "soda" — softens skin, leaves it smooth.
Known good for
- Aches & jointsstiff shoulders
- Smooth skindry, rough skin
- Recoveryfatigue, stress
A simple thermal spring drawn from Miharayama Onsen's No. 5 well at a remarkable 84 °C — one of the hotter natural sources on Izu Oshima, cooled before bathing. Neutral pH, hypotonic, and lightly mineralized (0.85 g/kg dissolved solids), so the water reads as quietly gentle on the skin rather than mineral-heavy. What sets it apart is a generous 333.8 mg/kg of metasilicic acid: enough to leave the thin silica film that gives the classic Japanese "beauty-water" feel, smoothing the skin after a soak. Colourless and clear at the wellhead, with no odour and a faint bitter note on the tongue.
Sampled at wellhead·Analyzed Nov 9, 2018·株式会社東京水質研究所·Cert no. C9310003
