Horita no Yu is a sodium-magnesium bicarbonate spring in the juso-sen style, with a salty edge from its chloride sub-type. Neutral in pH and moderately mineralized, the water has noticeable body; it runs colorless and clear, very faintly salty on the lips and almost odorless. A generous 255 mg/kg of metasilicic acid places it in Japan's beauty-water family, leaving a thin silica film that makes skin feel noticeably smoother afterwards.
Good for
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
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
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, netto 熱の湯).
cold sensitivity
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⁺253mgP59 national60%
- Magnesiummild; a laxative if you drink itMg²⁺45.7mgP85 national21%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺44.5mgP55 national12%
- Potassiumminor; matters for drinking limitsK⁺42.9mgP82 national6%
- LithiumLi⁺0.50mgP52 national0.4%
- ManganeseMn²⁺0.80mgP74 national0.2%
- Iron (II)Fe²⁺0.30mgP43 national0.1%
- StrontiumSr²⁺0.30mgP52 national0.1%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻541mgP78 national49%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻219mgP58 national34%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻147mgP61 national17%
- BromideBr⁻0.60mgP50 national0.1%
- Hydrogen phosphateHPO₄²⁻0.40mgP68 national0.1%
- FluorideF⁻0.20mgP16 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃255mgP95 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂8.1mgP49 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂35.2mgP62 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.04mgP46 national
- 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.