A gentle simple thermal spring classified as an alkaline simple onsen. At a wellhead pH of 9.0 it is alkaline enough to give the slippery, soft feel of Japan's beauty-water family. Lightly mineralized at just 0.41 g/kg of dissolved solids, the water is almost colorless and transparent, tasteless and odorless.
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
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
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⁺84.7mgP26 national68%
- Potassiumminor; matters for drinking limitsK⁺3.6mgP30 national2%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺0.50mgP1 national
- Magnesiummild; a laxative if you drink itMg²⁺0.10mgP11 national
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- CopperCu²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻144mgP61 national56%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻61.1mgP31 national32%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻31.7mgP19 national10%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻3.6mgP30 national2%
- HydroxideOH⁻0.20mgP66 national0.2%
- Iodideyellows in air; helps blood lipidsI⁻0.08mgP30 national
- Bromidetrace, sea-originBr⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃48.1mgP27 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂2.1mgP20 national
- Metaarsenious acidHAsO₂0.20mgP70 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.0000mg
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.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- 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.