七里田温泉「木乃葉の湯」Shichirida Onsen Konoha-no-Yu Source
A magnesium- and sodium-led bicarbonate-sulfate spring — weakly alkaline and soft on the skin, the bicarbonate softness layered with quiet sulfate body. At the wellhead the water is faintly yellow and clear with a metallic iron note, and turns slightly cloudy as the iron oxidizes on standing. A generous 234 mg/kg of metasilicic acid leaves the kind of 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
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
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
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.
- Magnesiummild; a laxative if you drink itMg²⁺281mgP98 national50%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺397mgP70 national37%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺83.0mgP67 national9%
- Potassiumminor; matters for drinking limitsK⁺59.9mgP86 national3%
- StrontiumSr²⁺0.80mgP76 national0.1%
- Manganesetrace; companion to iron springsMn²⁺0.60mgP68 national
- AmmoniumNH₄⁺0.14mgP25 national
- LithiumLi⁺0.12mgP30 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.0000mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,830mgP95 national65%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻549mgP88 national25%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻158mgP49 national10%
- FluorideF⁻0.20mgP17 national0.0%
- Bromidetrace, sea-originBr⁻0.30mgP36 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃234mgP92 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂10.9mgP58 national
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂377mgP94 national
- LeadPb0.02mgP78 national
- ArsenicAs< —mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —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.
- 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.