A sodium-calcium-magnesium sulfate spring with a bicarbonate sub-type — settled, mineral-rich body with bicarbonate softness layered in. Neutral pH and 46.6 °C at the source, with metasilicic acid at 127.7 mg/kg leaving a thin silica film for noticeably smoother skin. A modest 18 mg/kg of free hydrogen sulfide gives the water a faint rotten-egg note and a metallic edge at the wellhead.
Good for
Aches & joints
Warmth eases stiffness and raises the pain threshold. Radon and sulfate springs show the strongest evidence for joint and muscle pain.
stiff shoulders
Skin conditions
Sulfur and acidic waters are antibacterial and keratolytic, studied for atopic dermatitis and psoriasis.
atopic skin, eczema
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
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
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
Sensitive-skin caution
Strongly acidic or sulfur-rich water can sting broken, atopic-flare, or dry elderly skin. Ease in slowly and rinse off if it stings.
broken or dry skin
- 急性疾患(特に熱のある場合)
- Active tuberculosis
- Malignant tumor
- 重い心臓病
- 呼吸不全
- Renal failure
- Bleeding disorders
- Severe anemia
- その他一般に病勢進行中の疾患
- 妊娠中(特に初期と末期)
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⁺211mgP53 national54%
- Magnesiummild; a laxative if you drink itMg²⁺42.0mgP84 national22%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺75.6mgP66 national20%
- Potassiumminor; matters for drinking limitsK⁺23.4mgP68 national4%
- Iron (II)Fe²⁺2.0mgP72 national0.4%
- LithiumLi⁺0.20mgP40 national0.2%
- StrontiumSr²⁺0.50mgP68 national0.1%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻547mgP88 national66%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻219mgP59 national21%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻82.3mgP36 national13%
- Hydrogen sulfideHS⁻0.60mgP59 national0.1%
- FluorideF⁻0.40mgP31 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃128mgP64 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.8mgP36 national
- Metaarsenious acidHAsO₂< —mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S18.0mgP97 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂17.5mgP49 national
Measured at the source
On the certificate
- Chronic digestive disorders
- Cold sensitivity
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.
- Tei C, Kihara T. Waon Therapy for Chronic Heart Failure. J. Cardiology 53(2):214–218, 2009.
- Coavoy-Sánchez SA et al. Hydrogen sulfide and dermatological diseases. Int. J. Dermatology, 2019.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Akiyama H et al. Antimicrobial effects of acidic hot-spring water on S. aureus. J. Dermatological Science 24(3):193–200, 2000.
- Toriyama T et al. Carbon dioxide foot bathing on critical limb ischemia. International Angiology 21(4):367–373, 2002.
- Donaubauer AJ et al. Serial radon spa therapy on pain in musculoskeletal disorders. Frontiers in Immunology, 2024.
- Verhagen AP et al. Balneotherapy for rheumatoid arthritis. Cochrane Database of Systematic Reviews CD000518, 2015.
- 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.
- Ministry of the Environment, Japan. 禁忌症及び入浴又は飲用上の注意事項 (2014 notice).official