Shinmeidaki-no-yu is a blended source; the certificate names it as a mix of the Shibu Onsen central source and Tera-no-yu, and the result is a sodium-calcium sulfate-chloride spring. Neutral in pH and moderately mineralized at 1,218 mg/kg, it has genuine body, with a salty edge from the chloride side. The water is almost colorless and clear, yet it carries a metallic iron note and a faint saltiness on the lips, and the sample was drawn at the bath inlet rather than at the wellhead. A generous 148.7 mg/kg of metasilicic acid places it in Japan's beauty-water family, leaving the kind of silica film that makes skin feel noticeably smoother afterwards.
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
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
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⁺207mgP53 national56%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺110mgP76 national34%
- Magnesiummild; a laxative if you drink itMg²⁺8.5mgP59 national4%
- Potassiumminor; matters for drinking limitsK⁺19.0mgP61 national3%
- Aluminumshows up in acidic volcanic waterAl³⁺2.6mgP82 national2%
- Iron (II)Fe²⁺2.0mgP74 national0.4%
- LithiumLi⁺0.50mgP52 national0.4%
- ManganeseMn²⁺0.40mgP61 national0.1%
- StrontiumSr²⁺0.40mgP61 national0.1%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻395mgP81 national51%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻273mgP62 national48%
- BicarbonateHCO₃⁻10.0mgP6 national1.0%
- FluorideF⁻1.3mgP52 national0.4%
- BromideBr⁻1.5mgP68 national0.1%
- IodideI⁻0.30mgP61 national0.0%
- NitrateNO₃⁻0.04mgP19 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃149mgP68 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂37.7mgP84 national
- Metaarsenious acidHAsO₂0.70mgP84 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂15.5mgP47 national
- 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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- 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.