竹瓦温泉（男湯）Takegawara Onsen (Men's Bath)
A sodium-calcium-magnesium chloride spring with bicarbonate softness layered in, salty and heat-retaining but rounded rather than sharp. Weakly alkaline and gentle on the skin, it carries a moderate 1,490 mg/kg of dissolved solids, enough body to feel without weighing the water down. Metasilicic acid runs to 214 mg/kg, leaving the thin silica film that places this spring in Japan's beauty-water family; the analysis posted at the bathhouse lists cuts, burns and chronic skin conditions among its documented uses.
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, netto 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
Take care
From a certificate analyzed in 2019.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate.
- Acute illness
- Active tuberculosis
- Malignant tumor
- Severe heart disease
- Bleeding disorders
- Severe anemia
- Respiratory failure
- Renal failure
- Any other illness in an actively progressing stage
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⁺181mgP47 national42%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺102mgP74 national27%
- Magnesiummild; a laxative if you drink itMg²⁺59.2mgP87 national26%
- Potassiumminor; matters for drinking limitsK⁺27.9mgP73 national4%
- LithiumLi⁺1.1mgP76 national0.8%
- ManganeseMn²⁺1.0mgP77 national0.2%
- Iron (II)Fe²⁺0.70mgP59 national0.2%
- AmmoniumNH₄⁺0.30mgP39 national0.1%
- StrontiumSr²⁺0.60mgP73 national0.1%
- BariumBa²⁺0.20mgP72 national0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻353mgP70 national52%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻475mgP75 national41%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻68.7mgP47 national7%
- BromideBr⁻1.2mgP64 national0.1%
- Fluoridetrace; drinking limits applyF⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃214mgP89 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂3.7mgP27 national
- Metaarsenious acidHAsO₂0.10mgP53 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂17.6mgP49 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.08mgP62 national
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
From a certificate analyzed in 2019.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate. Items marked † were dropped from the official list then.
- Motor paralysis
- Chronic digestive disorders
- Hemorrhoids
- Cold sensitivity
- Chronic skin conditions (dropped from the official list in 2014)
- Chronic gynecological conditions (dropped from the official list in 2014)
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.