A gentle alkaline simple thermal spring, named Ruri-no-Yu on the posted analysis. The alkalinity is high enough to give the slippery, soap-like feel that places it in Japan's beauty-water family, while the dissolved load stays light — sulfate and bicarbonate lead the anions, with a little carbonate alongside them. The posted indications run through the standard list: neuralgia, muscle and joint pain, frozen shoulder, bruises and sprains, chronic digestive complaints, cold sensitivity, convalescence and fatigue recovery.
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
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 1990.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate.
- Severe heart disease
- Respiratory failure
- Renal failure
- Bleeding disorders
- Severe anemia
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⁺99.1mgP27 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺6.1mgP19 national
- Potassiumminor; matters for drinking limitsK⁺1.3mgP14 national
- Sulfate"gypsum / Glauber's salt": vessels and wound healingSO₄²⁻97.2mgP54 national
- Bicarbonate"soda": softens skin, leaves it smoothHCO₃⁻77.9mgP40 national
- Chloridetable-salt anion: coats the skin and holds heat inCl⁻21.2mgP16 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻11.6mgP51 national
- Fluoridetrace; drinking limits applyF⁻9.9mgP89 national
Measured at the source
On the certificate
From a certificate analyzed in 1990.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate.
- Neuralgia
- Muscle pain
- Joint pain
- Frozen shoulder
- Motor paralysis
- Bruises
- Sprains
- Chronic digestive disorders
- Hemorrhoids
- Cold sensitivity
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.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- 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.