Oku no Yu
Analysis VerifiedNoboribetsu Onsen, boasting Hokkaido's most celebrated geothermal landscape including the dramatic Jigokudani (Hell Valley), has long captivated visitors with its abundant flow and remarkable diversity of mineral compositions. The Oku-no-Yu source emerges naturally from the depths of pristine wilderness, distinguished by its milky-white waters and subtle sulfur aroma that sweeps away the cares of daily life. This spring is especially recommended for those seeking to immerse themselves fully in the essence of hot spring bathing or yearning to soothe accumulated fatigue deep within the embrace of nature.
The bar length shows how abundant each component is compared to thresholds that make it "distinctive" (therapeutic spring standards, beauty spring criteria, etc.).
Undissociated boric acid with antibacterial action that keeps the skin surface clean.
The source of the distinctive sulfur smell. Dilates blood vessels via skin and inhalation to strongly boost circulation.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
Tightens the skin and balances sebum.
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.
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.
Given its sulfur-rich composition and high temperature (73.3°C from source), verify that water has been appropriately cooled or diluted before entry. Due to its weakly acidic nature (pH 4.76), initial sessions should be limited to 10–15 minutes to acclimate your skin. After bathing, rinse briefly with shower water to prevent excessive sulfur residue; complete the rinse swiftly to preserve therapeutic minerals on your skin.
The weakly acidic pH 4.76 and hydrogen sulfide-type sulfur compounds gently exfoliate skin, offering relief for those with atopic dermatitis and chronic dermatological conditions. Sodium and calcium chloride minerals penetrate deeply to warm the body core, historically supporting recovery from chronic rheumatoid arthritis and motor nerve dysfunction. With a low osmotic concentration of 1.699g/kg total dissolved solids, this spring's mild mineral intensity suits prolonged therapeutic bathing courses.
Those with serious cardiovascular conditions—heart disease, hypertension, arteriosclerosis—or malignant tumors and active tuberculosis should refrain from bathing. High temperatures demand particular caution: avoid prolonged immersion or bathing after alcohol consumption.
※ See the analysis data below for detailed contraindications
ANALYSIS DATAView all analysis fields ▼
Source Info
- Source name
- 奥の湯
- Spring type
- 含硫黄－ナトリウム・カルシウム－塩化物泉（硫化水素型）
- Old spring type name
- 含硫黄ーナトリウム・カルシウム-塩化物泉 (硫化水素型) (弱酸性低張性高温泉)
- Source temperature
- 73.3℃
- pH
- 4.7
- Flow rate
- 75 L/min
- Flow type
- 自然湧出
- Osmotic pressure
- 低張性
Analysis Document
- Analysis date
- 2008-07-28
- Analyst organization
- 北海道立衛生研究所
- Registration No.
- 北海道第1号
Cations
- Sodium ion Na⁺
- 343 mg/kg
- Potassium ion K⁺
- 80.4 mg/kg
- Ammonium ion NH₄⁺
- 1.3 mg/kg
- Magnesium ion Mg²⁺
- 7.0 mg/kg
- Calcium ion Ca²⁺
- 108 mg/kg
- Aluminum ion Al³⁺
- 0.40 mg/kg
- Manganese ion Mn²⁺
- 0.60 mg/kg
- Iron(II) ion Fe²⁺
- 1.1 mg/kg
- Iron(III) ion Fe³⁺
- 0.60 mg/kg
- Zinc ion Zn²⁺
- 0.00 mg/kg
- Lead ion Pb²⁺
- 0.00 mg/kg
- Copper ion Cu²⁺
- 0.00 mg/kg
- Cadmium ion Cd²⁺
- 0.00 mg/kg
- Total cations
- 0.54 mg/kg
Anions
- Fluoride ion F⁻
- 0.50 mg/kg
- Chloride ion Cl⁻
- 809 mg/kg
- Hydrogen sulfide ion HS⁻
- 0.10 mg/kg
- Thiosulfate ion S₂O₃²⁻
- 20.5 mg/kg
- Sulfate ion SO₄²⁻
- 32.9 mg/kg
- Bicarbonate ion HCO₃⁻
- 6.1 mg/kg
- Carbonate ion CO₃²⁻
- 0.00 mg/kg
- Total anions
- 0.87 mg/kg
Undissociated Components
- Arsenious acid HAsO₂
- 0.30 mg/kg
- Metasilicic acid H₂SiO₃
- 148 mg/kg
- Metaboric acid HBO₂
- 81.6 mg/kg
- Total undissociated
- 0.23 mg/kg
Dissolved Gas
- Free carbon dioxide CO₂
- 43.0 mg/kg
- Free hydrogen sulfide H₂S
- 14.6 mg/kg
- Total dissolved gas
- 0.06 mg/kg
Trace Components
- Radon Rn
- 0.011 mE/kg
Totals
- Component total
- 1.7 mg/kg
- Evaporation residue
- 1.7 mg/kg
Usage
- Heating
- No
- Dilution
- Yes（Water is diluted at many facilities depending on the season due to high source temperature.）
- Recycle / Filter
- Recycled
- Additives
- No
- Disinfection
- Yes
Drinking
- Drinkability
- Not drinkable
