Okunosawa Funkisen

Analysis Unverified
奥の沢噴気泉
Spring Born of Steam

Okunosawa Funkisen is fed by volcanic fumaroles venting in the Okunosawa ravine at Yumoto Omaru in Nasu. Its origin traces the volcanic life of Mount Nasu directly, and among the naturally welling springs of the Omaru area it is the odd one out — the only one drawn from steam rather than water. Arriving at 70.4°C, it is all but colourless and clear yet carries a faint smell of hydrogen sulphide; on the tongue it turns slightly sour, then bitter, then astringent. Left to stand for forty-eight hours it throws a pale yellow-white precipitate, making its sulphur visible. It suits anyone drawn to the scent of sulphur, or curious to feel a volcano breathing through the water.

AI Generated
SPRING TYPE
Sulfur Spring

These springs have an aroma that recalls boiled-eggs and can be cloudy white, blue or green. They boast strong antibacterial qualities and can be effective at healing wounds and relieving inflammatory skin conditions while also promoting circulation.

See features & indications
Bathing indications
Atopic dermatitisPlaque psoriasisChronic eczemaEpidermal suppuration
Drinking indications
Impaired glucose tolerance (diabetes)Dyslipidemia (high cholesterol)

※ Only at facilities permitted to serve drinking water. 200–500 mL/day recommended.

Cautions
  • 皮膚または粘膜の敏感な方、高齢者の皮膚乾燥症の方は禁忌です。
  • 肌が弱い方は入浴後に真湯で洗い流してください。
Definition :Contains 2 mg/kg or more of total sulfur.
Source: 環境省「あんしん・あんぜんな温泉利用のいろは」(監修:日本温泉気候物理医学会)Read full article
PH VALUE
4.3
Mildly Acidic
Acidic ← 07 Neutral14 → Alkaline
Mildly acidic springs (pH 3-6) per Japan Ministry of Environment classification. Refreshing bathing experience with relatively low skin irritation.
TEMPERATURE
70.4
Very Hot Spring
Near boiling, extremely hot. Requires substantial cooling or dilution.
KEY MINERALS

The bar length shows how abundant each component is compared to thresholds that make it "distinctive" (therapeutic spring standards, beauty spring criteria, etc.).

Free hydrogen sulfideSee detail
5.0 mg/kg

The source of the distinctive sulfur smell. Dilates blood vessels via skin and inhalation to strongly boost circulation.

Metasilicic acidSee detail
66.3 mg/kg

A natural moisturizer that leaves a hydrated feel on the skin.

Aluminum ionSee detail
1.0 mg/kg

Tightens the skin and balances sebum.

Sulfate ionSee detail
157 mg/kg

Soothes the skin and gently improves circulation.

Calcium ionSee detail
47.9 mg/kg

Gentle astringent action that conditions the skin.

CHARACTER · COMPOSITION PROFILE
1234StimulationBactericidalSkin BeautyHeat RetentionRelaxation

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.

USAGE
Free-Flowing Onsen
Pure spring water — no dilution, no recirculation
HeatedNo
DilutedNo
RecycledNo
FilteredNo
DisinfectedNo
AdditivesNo
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.

SENSORY TEST
Color
殆ど無色澄明
Smell
弱硫化水素臭
Taste
微酸味、微苦味のち微渋味
EFFECTS
Spring-specific indications (bathing)
Atopic dermatitisPlaque psoriasisChronic eczemaEpidermal suppuration
General indications (bathing)
High blood pressure (mild)Rheumatoid arthritisAutonomic instabilityInsomniaDepressionChronic pain or stiffness in muscles and jointsMuscle stiffness due to motor paralysisGastrointestinal dysfunction
Contraindications
Acute illness (especially with fever)Active tuberculosisMalignant tumorsSevere heart diseaseRespiratory failureRenal failureBleeding disordersSevere anemiaAny actively progressing illnessPregnancy (especially early and late stages)Severe chronic dermatitis (sulphur springs)
BATHING TIPS
AI Generated

It arrives at 70.4°C and carries hydrogen sulphide, so check that the room is well ventilated and keep to short soaks of five to ten minutes rather than one long one. Mildly acidic at pH 4.32, it can sting sensitive skin — a light rinse in fresh water afterwards settles it.

EFFECT STORY
AI Generated

Carrying 5.0 mg/kg of free hydrogen sulphide at a mildly acidic pH 4.32, this water softens the skin while working on circulation — the signature of a sulphur spring, with which immune system stimulation is traditionally associated. It lends itself to balneotherapy on a day you want the volcanic country to reset you.

CAUTIONS
AI Generated

As a sulphur spring it asks care of anyone with fragile skin or mucous membranes, and of older bathers with dry skin. Avoid bathing with acute illness or fever, active tuberculosis, malignant tumours or serious heart disease.

※ See the analysis data below for detailed contraindications

ANALYSIS DATAView all analysis fields ▼

Source Info

Source name
Okunosawa Funkisen
Spring type
Simple Sulfur Hot Spring (hydrogen sulfide type)
Source temperature
70.4℃
pH
4.32
Osmotic pressure
低張性

Analysis Document

Analysis date
2020-12-22
Analyst organization
一般社団法人 栃木県薬剤師会 検査センター
Registration No.
14栃薬第1号

Cations

Hydrogen ion H⁺
0.10 mg/kg
Lithium ion Li⁺
0.00 mg/kg
Sodium ion Na⁺
7.8 mg/kg
Potassium ion K⁺
1.5 mg/kg
Ammonium ion NH₄⁺
0.00 mg/kg
Magnesium ion Mg²⁺
5.4 mg/kg
Calcium ion Ca²⁺
47.9 mg/kg
Aluminum ion Al³⁺
1.0 mg/kg
Manganese ion Mn²⁺
0.30 mg/kg
Iron(II) ion Fe²⁺
0.90 mg/kg
Iron(III) ion Fe³⁺
0.00 mg/kg
Zinc ion Zn²⁺
0.00 mg/kg
Lead ion Pb²⁺
< 0.005 mg/kg
Strontium ion Sr²⁺
0.00 mg/kg
Barium ion Ba²⁺
0.00 mg/kg
Copper ion Cu²⁺
< 0.005 mg/kg
Cadmium ion Cd²⁺
< 0.005 mg/kg
Total cations
0.06 mg/kg

Anions

Fluoride ion F⁻
0.00 mg/kg
Chloride ion Cl⁻
1.4 mg/kg
Hydroxide ion OH⁻
0.00 mg/kg
Hydrogen sulfide ion HS⁻
0.00 mg/kg
Thiosulfate ion S₂O₃²⁻
1.1 mg/kg
Sulfate ion SO₄²⁻
157 mg/kg
Bicarbonate ion HCO₃⁻
0.00 mg/kg
Carbonate ion CO₃²⁻
0.00 mg/kg
Bromide ion Br⁻
0.00 mg/kg
Iodide ion I⁻
0.00 mg/kg
Hydrogen sulfate HSO₄⁻
0.30 mg/kg
Hydrogen thiosulfate HS₂O₃⁻
0.00 mg/kg
Nitrite ion NO₂⁻
0.00 mg/kg
Nitrate ion NO₃⁻
0.00 mg/kg
Dihydrogen phosphate H₂PO₄⁻
0.00 mg/kg
Hydrogen phosphate HPO₄²⁻
0.00 mg/kg
Phosphate ion PO₄³⁻
0.00 mg/kg
Arsenite ion AsO₂⁻
0.00 mg/kg
Sulfide ion S²⁻
0.00 mg/kg
Hydrogen metasilicate HSiO₃⁻
0.00 mg/kg
Metasilicate ion SiO₃²⁻
0.00 mg/kg
Metaborate ion BO₂⁻
0.00 mg/kg
Total anions
0.16 mg/kg

Undissociated Components

Sulfuric acid H₂SO₄
0.00 mg/kg
Phosphoric acid H₃PO₄
0.00 mg/kg
Arsenious acid HAsO₂
0.00 mg/kg
Metasilicic acid H₂SiO₃
66.3 mg/kg
Metaboric acid HBO₂
0.40 mg/kg
Total undissociated
0.07 mg/kg

Dissolved Gas

Free carbon dioxide CO₂
0.00 mg/kg
Free hydrogen sulfide H₂S
5.0 mg/kg
Total dissolved gas
0.01 mg/kg

Totals

Total dissolved substances
0.29 mg/kg
Component total
0.30 mg/kg
Evaporation residue
0.30 mg/kg

Usage

Heating
No
Dilution
No
Recycle / Filter
No
Additives
No
Disinfection
No

Indications & Contraindications

Bathing indications
Atopic dermatitis, Plaque psoriasis, Chronic eczema, Epidermal suppuration
General indications
High blood pressure (mild), Rheumatoid arthritis, Autonomic instability, Insomnia, Depression, 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), Severe chronic dermatitis (sulphur springs)

Drinking

Drinkability
Not drinkable
FACILITY INFO
AI draft (unverified)
Official site
Tattoo
No tattoosGuests with tattoos are strictly prohibited from using the facilities, in accordance with police guidance.
Private bath (Kashikiri)
Available
Bathing wear (Yuami-gi)
Free rental
About tattoos and onsen
Travelers with tattoos can still bathe comfortably in a private bath (Kashikiri) or a room with a private open-air bath.
Hours
Weekdays: 11:3015:00
Weekends & holidays: 11:3015:00
Last admission for day-use bathing is 14:30. Overnight guests can use the baths 24 hours, except during cleaning (10:00-11:30).
Closed days: Irregular holidays
Transit
Approx. 70 min by local bus (Kanto Bus) from JR Tohoku Shinkansen Nasushiobara Station (JR Tōhoku Shinkansen Nasushiobara Eki) (reservation required 2 days in advance, round trip 500 yen). Approx. 30 min by car from Tohoku Expressway Nasu IC (Tōhoku Jidōshadō Nasu IC).
Parking
Available, 30 spaces, free. *This is the Prefectural Oomaru Parking Lot (Ken'ei Oomaru Chūshajō) located just before the ryokan.
Day use fee
¥1,300Adult price. Children (3 years old to elementary school age) 1,000 yen. Includes face towel and bathing wear.
Facilities
Public BathOpen-air BathPrivate BathDrinking SpringGift ShopTea LoungeRest Area
House rules
No photography in the bath area
The facility is built on a slope, so there are many stairs. Please contact us in advance if you have difficulty walking.
Sources
This information may change without notice. Please contact the facility directly for accurate details.
How Long to Stay (Toji)
Start with 2 nights / 3 days

Japan’s Ministry of the Environment notes that even a short stay refreshes you. For a full therapeutic cure, around 2–3 weeks is the guideline.

More on toji length
Nearby Onsen with the Same Spring Type
The descriptions, catch phrases, and translations on this page are generated by AI (Claude). pH, temperature, and component values are OCR-extracted from the official analysis report. Learn more