A blended source served from a storage tank at Matsuya in Hijiori Onsen: three communal wells (Kumiai No.2, No.3, No.5) plus the inn's own Matsuya No.1, combined before delivery. The chemistry is sodium-led chloride water with bicarbonate softness layered in — a salty, heat-retaining body softened by a HCO₃ finish. At the wellhead the water is faintly cloudy with a salt, iron and astringent bite to the tongue; in the lab sample it yellows to a pale tint, the trace iron oxidizing on contact with air. Metasilicic acid runs a generous 121 mg/kg, putting it in the Japanese 'beauty-water' family with a soft, smoothing feel on the skin.
Good for
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
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
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⁺572mgP78 national82%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺59.7mgP60 national10%
- Magnesiummild; a laxative if you drink itMg²⁺14.6mgP67 national4%
- Potassiumminor; matters for drinking limitsK⁺42.8mgP81 national4%
- Iron (II)Fe²⁺1.4mgP67 national0.2%
- LithiumLi⁺1.1mgP76 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻615mgP76 national58%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻600mgP80 national33%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻134mgP59 national9%
- BromideBr⁻1.3mgP65 national0.1%
- FluorideF⁻0.10mgP9 national0.0%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻0.20mgP12 national
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃121mgP62 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂35.9mgP83 national
- Metaarsenious acidHAsO₂1.1mgP90 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂220mgP89 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —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.
- 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.