A simple sulfur spring: colorless and clear, yet carrying a mid-strength rotten-egg note of hydrogen sulfide and a distinct sulfurous taste. Hydrogen sulfide ion reaches 31 mg/kg — many times the threshold that earns a spring its sulfur designation — with a little more arriving as free H₂S. The water is weakly alkaline and soft on the skin, and at 0.77 g/kg of dissolved solids it stays light rather than assertive; 98.5 mg/kg of metasilicic acid leaves the thin silica film that puts it in Japan's beauty-water family. The sample was drawn not at the wellhead but at the distribution box that splits the water out toward the baths.
Good for
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
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
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
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⁺159mgP41 national72%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺51.1mgP57 national27%
- PotassiumK⁺3.3mgP27 national0.8%
- AmmoniumNH₄⁺1.3mgP71 national0.7%
- StrontiumSr²⁺0.40mgP62 national0.1%
- MagnesiumMg²⁺0.10mgP11 national0.1%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻285mgP71 national58%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻81.8mgP35 national23%
- Hydrogen sulfidesulfur character — antibacterialHS⁻31.0mgP98 national9%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻42.7mgP26 national7%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻9.0mgP47 national3%
- FluorideF⁻0.80mgP43 national0.4%
- Bromidetrace, sea-originBr⁻0.30mgP37 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃98.5mgP53 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂6.2mgP43 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S1.5mgP79 national
- ArsenicAsNDmg
- CadmiumCdNDmg
- ChromiumCrNDmg
- Mercurytoxic trace — part of the drinking-safety checkHgNDmg
- LeadPbNDmg
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.
- 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