An alkaline simple thermal spring drawn from the Mogami-Nishi-Hakone Kamiyama No. 1 well in Gotenba. At pH 8.96 the water carries the slippery, soft-on-skin feel of Japan's beauty-water family, while a light mineralization of 345 mg/kg keeps it gentle and unobtrusive. The wellhead emerges at 32.7 °C — a cool source that is reheated for bathing.
Good for
Smooth skin
Bicarbonate and alkalinity gently lift dead keratin while silica hydrates, leaving skin smooth. This is the basis of the beautifying-water (bijin-no-yu 美人の湯) reputation.
dry, rough skin
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Full composition
The bar is each ion's share of charge (mval%) within its group; over 20% names the spring. Gases, silica and trace metals are measured by mass only.
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺69.0mgP20 national89%
- Potassiumminor; matters for drinking limitsK⁺6.5mgP38 national5%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺3.4mgP13 national5%
- MagnesiumMg²⁺0.40mgP18 national0.9%
- Manganesetrace; companion to iron springsMn²⁺0.09mgP25 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.08mgP18 national
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- CopperCu²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻120mgP47 national49%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻39.9mgP24 national28%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻16.2mgP59 national14%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻17.1mgP30 national9%
- HydroxideOH⁻0.20mgP67 national0.3%
- Hydrogen phosphateHPO₄²⁻0.0000mg
- Bromidetrace, sea-originBr⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃70.5mgP44 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂2.0mgP18 national
- Metaarsenious acidHAsO₂< —mg
Measured at the source
Evidence
- Maeda M. 温泉の医学的効果とその科学的根拠. J. Hot Spring Science 70:197–207, 2021.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Li H et al. Bicarbonate Ionized Water Bathing Enhances Natural Killer Cell Activity. Scientific Reports 14:51851, 2024.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.