A hot 85.9 degC sulfate-led spring from a sodium-dominant source, layered with bicarbonate softness and a salty chloride finish. Neutral pH and moderate mineralization (1,350 mg/kg) give it noticeable body without sharpness. Metasilicic acid runs unusually high at 329.7 mg/kg, leaving the kind of thin silica film that makes skin feel noticeably smoother afterwards. At the wellhead the water carries a faintly astringent taste and a slight iron note.
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
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
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
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
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⁺205mgP52 national64%
- Magnesiummild; a laxative if you drink itMg²⁺23.8mgP72 national14%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺31.2mgP47 national11%
- Potassiumminor; matters for drinking limitsK⁺53.8mgP85 national10%
- LithiumLi⁺0.20mgP40 national0.6%
- Iron (III)Fe³⁺0.90mgP85 national0.4%
- Iron (II)Fe²⁺0.40mgP48 national0.1%
- StrontiumSr²⁺0.20mgP44 national0.0%
- ManganeseMn²⁺0.10mgP36 national0.0%
- AmmoniumNH₄⁺0.05mgP14 national0.0%
- Aluminumshows up in acidic volcanic waterAl³⁺NDmg
- BariumBa²⁺NDmg
- CopperCu²⁺NDmg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺NDmg
- ZincZn²⁺NDmg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻262mgP71 national39%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻289mgP64 national34%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻137mgP46 national28%
- BromideBr⁻0.50mgP47 national0.0%
- FluorideF⁻0.10mgP9 national0.0%
- Hydrogen phosphateHPO₄²⁻NDmg
- Hydrogen sulfidesulfur character — antibacterialHS⁻NDmg
- Iodideyellows in air; helps blood lipidsI⁻NDmg
- NitrateNO₃⁻NDmg
- HydroxideOH⁻NDmg
- Thiosulfateoxidized sulfurS₂O₃²⁻NDmg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃330mgP98 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂10.9mgP58 national
- Metaarsenious acidHAsO₂< —mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂104mgP79 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ChromiumCrNDmg
- Radonfaint radon — studied for joint pain (hormesis)Rn—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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- 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.
- 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.