A calcium- and sodium-led sulfate spring, weakly mineralized at 1,758 mg/kg dissolved solids. Alkaline pH gives the slippery feel of Japan's beauty-water family, while the sulfate base brings quiet, settled body to the soak. Source temperature of 39 degrees Celsius leaves it pleasantly lukewarm — well-suited to long, unhurried bathing.
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
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
From a certificate analyzed in 2012.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate. Items marked † were removed from the official list of contraindications then, or include a condition that was. If you have a health condition, ask a doctor before bathing.
- Acute illness (especially when fever is present)
- Active tuberculosis
- Malignant tumor
- Severe heart disease
- Respiratory failure
- Renal failure
- Bleeding disorders
- Severe anemia
- Severe arteriosclerosis
- Hypertension
- Pregnancy (especially the early and late stages) (dropped from the official list in 2014)
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.
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺368mgP91 national
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺128mgP36 national
- Potassiumminor; matters for drinking limitsK⁺4.5mgP33 national
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻1,153mgP98 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻86.1mgP37 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻5.5mgP3 national
- Bromidetrace, sea-originBr⁻< —mg
- Carbonatestrongly alkaline; slippery feelCO₃²⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- NitrateNO₃⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃31.9mgP14 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.60mgP9 national
- Metaarsenious acidHAsO₂0.02mgP31 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.60mgP15 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
From a certificate analyzed in 2012.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate. Items marked † were dropped from the official list then.
- Chronic skin conditions (dropped from the official list in 2014)
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.
- 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.