A cold-mineral chloride spring (19.5 C at the wellhead, heated for bathing) led by sodium, calcium and magnesium. The 'iron-bearing' prefix on the certificate is earned — total iron 26 mg/kg, enough that the water emerges clear at the source and turns yellow-brown and slightly turbid by the time it reaches the lab. Neutral pH, moderately mineralized at 5.4 g/kg total solute, with a faint iron-rust note and a light salty-mineral taste on the lips.
Good for
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, nettō 熱の湯).
cold sensitivity
Cuts
Mineral-rich chloride, sulfate and sulfur waters have a long-recorded soothing effect on minor cuts and slow-healing skin.
minor wounds
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
- 進行性の悪性腫瘍又は高度の貧血など身体衰弱の著しい場合
- 少し動くとも苦しくなるような重い心臓・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⁺941mgP81 national44%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺612mgP93 national33%
- Magnesiummild; a laxative if you drink itMg²⁺237mgP96 national21%
- FeTotalFe26.0mgP100 national1%
- ManganeseMn²⁺10.1mgP98 national0.4%
- PotassiumK⁺13.6mgP52 national0.4%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻3,019mgP88 national93%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻314mgP63 national6%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻83.8mgP52 national2%
- BO2BO₂⁻< —mg
- Carbonatestrongly alkaline; slippery feelCO₃²⁻< —mg
- Fluoridetrace; drinking limits applyF⁻< —mg
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- HSiO3HSiO₃⁻< —mg
- HydroxideOH⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃44.3mgP28 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.8mgP35 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂69.9mgP73 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs0.01mgP34 national
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- 筋肉又は関節の慢性的な痛み又はこわばり(関節リウマチ、変形性関節症、腰痛症、神経痛、五十肩、打撲、捻挫などの慢性期)
- Muscle stiffness associated with motor paralysis
- 胃腸機能の低下(胃もたれ、腸にガスがたまるなど)
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
- ストレスによる諸症状(睡眠障害など)
- Peripheral circulation disorders
- 冷え症
- Dry skin
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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.