Yasuda Onsen
Analysis UnverifiedYasuda Onsen rises in the farmland of Yasuda, Agano, on the right bank of the Agano River with the Gozu Mountains behind it. Pumped from underground at 19.9°C and 105 liters per minute, the water was found in its 2024 analysis to carry 23,161 mg of dissolved matter per kilogram—a "strong brine" with salinity approaching that of seawater. Sodium makes up about 85% of the cations and chloride more than 90% of the anions. It also contains 34.1 mg of iodide and 84.6 mg of bromide, hinting at ancient seawater trapped in the strata as fossil brine, along with a generous 413.7 mg of free carbon dioxide. Nearly colorless and clear, it tastes strongly salty with a faint metallic edge. Think of it as a taciturn Sea of Japan fisherman: plain at first sight, yet its dense, briny strength wraps the body firmly and leaves a warmth that lingers long after bathing.
The bar length shows how abundant each component is compared to thresholds that make it "distinctive" (therapeutic spring standards, beauty spring criteria, etc.).
Above 10 mg classifies the spring as an "iodine spring" — a rare type that delivers antibacterial and anti-inflammatory action through the skin.
Absorbed through the skin to gently calm nervous tension, leaving deep relaxation after the bath.
Salinity comparable to seawater. The salt film traps heat for outstanding warmth ("hot bath spring").
Salt forms a thin film on the skin, retaining heat after bathing. Helps with poor circulation.
A "beauty spring" that gently emulsifies dead skin cells, leaving skin smooth after bathing.
- Chloride (salt)12350 mg/kg
- Feel
- Tastes salty; the warmth lasts after you get out.
- Said to
- Salt is said to form a film on the skin that keeps in heat and moisture. Bathing indications include cuts, poor circulation and dry skin.
- Note
- May sting cuts. Strong salty water can tire you—avoid long soaks.
- Metasilicic acid93.2 mg/kg
- Feel
- Your skin may feel smoother.
- Said to
- 50 mg/kg or more is said to mark a “skin-beautifying spring”; it is also used in skincare.
- Note
- The “skin-beautifying” label is a common rule of thumb, not a legal standard.
Effects are general descriptions based on the Ministry of the Environment’s indications by spring type, not a guarantee.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
▸Note
The temperature, pH and component values shown here are based on the hot spring analysis (source). Actual values in the bath may differ depending on heating, dilution, recycling and filtration. Please check current usage status at the facility.
This hypertonic strong brine exceeds 23 g/kg of minerals and is fairly demanding on the body. Start with 3–5 minutes at a time and rest between soaks. Salt left on the skin prolongs the warmth, but those with sensitive skin may wish to rinse lightly afterward. Remember to rehydrate.
With 12,350 mg/kg of chloride, the brine is said to leave a thin salt film on the skin that slows evaporation, offering long-lasting restorative warmth. Hypertonic water traditionally associated with deep heating may also help relieve pain from chill and stiffness.
As a highly concentrated hypertonic brine, long or repeated hot soaks can cause bathing fatigue. Rinse with fresh water if your skin feels dry or itchy, and keep baths short if you have heart or blood-pressure concerns.
※ See the analysis data below for detailed contraindications
ANALYSIS DATAView all analysis fields ▼
Source Info
- Source name
- Yasuda Onsen
- Spring type
- Iodine-containing Sodium Chloride strong saline Cold Mineral Spring
- Source temperature
- 19.9℃
- pH
- 6.8
- Flow rate
- 105 L/min
- Flow type
- 動力揚湯
- Osmotic pressure
- 高張性
Analysis Document
- Analysis date
- 2024-04-03
- Analyst organization
- 一般財団法人新潟県環境分析センター
- Registration No.
- 新潟県（登）環企第4号
Cations
- Lithium ion Li⁺
- 0.70 mg/kg
- Sodium ion Na⁺
- 7346 mg/kg
- Potassium ion K⁺
- 424 mg/kg
- Ammonium ion NH₄⁺
- 460 mg/kg
- Magnesium ion Mg²⁺
- 119 mg/kg
- Calcium ion Ca²⁺
- 248 mg/kg
- Aluminum ion Al³⁺
- 0.00 mg/kg
- Manganese ion Mn²⁺
- 0.10 mg/kg
- Iron(II) ion Fe²⁺
- 2.5 mg/kg
- Zinc ion Zn²⁺
- 0.00 mg/kg
- Lead ion Pb²⁺
- < 0.005 mg/kg
- Strontium ion Sr²⁺
- 2.7 mg/kg
- Barium ion Ba²⁺
- 1.3 mg/kg
- Copper ion Cu²⁺
- 0.00 mg/kg
- Cadmium ion Cd²⁺
- < 0.001 mg/kg
- Total cations
- 8605 mg/kg
Anions
- Fluoride ion F⁻
- 0.00 mg/kg
- Chloride ion Cl⁻
- 12350 mg/kg
- Hydrogen sulfide ion HS⁻
- 0.00 mg/kg
- Thiosulfate ion S₂O₃²⁻
- 0.00 mg/kg
- Sulfate ion SO₄²⁻
- 15.0 mg/kg
- Bicarbonate ion HCO₃⁻
- 1556 mg/kg
- Carbonate ion CO₃²⁻
- 0.00 mg/kg
- Bromide ion Br⁻
- 84.6 mg/kg
- Iodide ion I⁻
- 34.1 mg/kg
- Hydrogen sulfate HSO₄⁻
- 0.00 mg/kg
- Nitrite ion NO₂⁻
- 0.00 mg/kg
- Nitrate ion NO₃⁻
- 3.3 mg/kg
- Hydrogen phosphate HPO₄²⁻
- 0.30 mg/kg
- Total anions
- 14043 mg/kg
Undissociated Components
- Metasilicic acid H₂SiO₃
- 93.2 mg/kg
- Metaboric acid HBO₂
- 6.4 mg/kg
- Total undissociated
- 99.6 mg/kg
Dissolved Gas
- Free carbon dioxide CO₂
- 414 mg/kg
- Free hydrogen sulfide H₂S
- 0.00 mg/kg
- Total dissolved gas
- 414 mg/kg
Totals
- Total dissolved substances
- 22748 mg/kg
- Component total
- 23161 mg/kg
- Evaporation residue
- 20850 mg/kg
Usage
- Usage status
- Unknown
Indications & Contraindications
- Bathing indications
- Cuts and grazes, Peripheral circulatory failure, Poor circulation, Depression, Xeroderma
- General indications
- High blood pressure (mild), Rheumatoid arthritis, Autonomic instability, Insomnia, Chronic pain or stiffness in muscles and joints, Muscle stiffness due to motor paralysis, Gastrointestinal dysfunction
- Contraindications
- Acute illness (especially with fever), Active tuberculosis, Malignant tumors, Severe heart disease, Respiratory failure, Renal failure, Bleeding disorders, Severe anemia, Any actively progressing illness, Pregnancy (especially early and late stages), Consult a doctor if you have thyroid disease (iodine springs)
Drinking
- Drinkability
- Not drinkable