A weakly alkaline cold-mineral spring (21.7 C source, pH 8.8) with a faint hydrogen sulfide note at the wellhead. Total dissolved solids sit just below 1 g/kg, so the certificate does not classify it as a therapeutic spring, but the alkaline chemistry still gives the water the soft, slippery hand of the classic Japanese beauty-water family. Because the source is below 25 C the bath is reheated, and it is also diluted, recirculated and chlorine-disinfected before reaching the tub.
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
Take care
- 病気の活動期(特に熱のあるとき)
- Active tuberculosis
- 進行した悪性腫瘍又は高度の貧血など身体衰弱の著しい場合
- 少し動くと息苦しくなるような重い心臓又は肺の病気
- むくみのあるような重い腎臓の病気
- 消化管出血
- 目に見える出血があるとき
- 慢性の病気の急性増悪期
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⁺283mgP60 national99%
- CalciumCa²⁺1.7mgP6 national0.6%
- PotassiumK⁺1.0mgP14 national0.2%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺< —mg
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻621mgP80 national83%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻39.0mgP88 national11%
- Fluoridetrace; drinking limits applyF⁻6.2mgP82 national3%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻8.9mgP12 national2%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻7.8mgP19 national1%
- Hydrogen sulfideHS⁻0.90mgP69 national0.2%
- HydroxideOH⁻0.10mgP50 national0.1%
- BO2BO₂⁻< —mg
- HSiO3HSiO₃⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃17.0mgP3 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂7.2mgP47 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂1.3mgP19 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs< —mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —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.