Spring Quality
Sodium - Chloride cold mineral springs
ナトリウム－塩化物冷鉱泉
(Isotonic, Weakly Alkaline, Cold mineral spring)
Hot springs for beautiful skin—
rich yet gentle—welling up at a secluded mountain inn
Hot springs are believed to form when rainwater or snowmelt seeps underground, or when ancient seawater becomes trapped deep within the earth. Heated by magma or the earthʼs internal heat, this water dissolves minerals from underground rocks and slowly rises to the surface over years—or even tens of thousands of years.
Onsen Components
*％＝mval％
Locks in moisture
Salts's bactericidal effect helps protect minor cuts “Hot springs for cuts”
Promotes blood circulation
Supports autonomic nervous system
Helps leave your skin smooth and silky “Hot springs for beautiful skin”
Provides a refreshing feeling after bathing
A skin-beautifying component that softens dead skin cells / Promotes blood circulationAbout 4.8 times
the hot spring standard (340 mg/kg)
Sodium hydrogen carbonate is formed when sodium ions (2,957 mg/kg) combine with hydrogen carbonate ions (1,191 mg/kg). When present at 340 mg/kg or more, it becomes a qualifying mineral component for a hot spring under Japan's Hot Springs Act. Commonly known as baking soda, sodium hydrogen carbonate emulsifies excess sebum, breaking it into tiny droplets that mix with water and making it easier to wash away. As a result, it helps soften dead skin cells, leaving the skin smooth and silky. It is one of the key components that gives a hot spring its reputation as a “Hot spring for beautiful skin”.
*The bars for Metasilicic acid 50 mg/kg and Metaboric acid 5 mg/kg represent the qualification criteria for hot springs. The number of bars indicates values such as “more than XX times the hot spring standard” or “about XX times the hot spring standard”.
■ Natural moisturizing component
■ Only 8 mg/kg short of the hot spring standard (50 mg/kg)
Metaboric Acid 22.7 mg/kg■ Helps keep the skin clean
■ About 4.5 times the hot spring standard (5 mg/kg)
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Total Dissolved Substances
(excluding gaseous)
8,739 mg/kg
58-87 times more components than commercial bath additives!
Hydrogen Ion
Concentration
pH 7.9
Weakly Alkaline
leaving your skin smooth and silky!
Spring Temperature
15.0 ℃
■ The water temperature is maintained by a circulation system
Color of water /
Smell of water
Clear and Colorless
Odorless
Hot Spring Flow Rate
48 L/min
(Private source / Mechanically pumped)
Hot spring water usage per person (spring discharge / maximum capacity)
→ 48 L / 60 guests ＝0.8 L / per minute
*To meet the requirements for kakenagashi (flowing directly from the source),
at least 1 liter of hot spring water per minute per bather
is required for proper bath management
Status of Source Utilization
| Water added | Heated | Disinfected | Circulated | Bath additives |
|---|---|---|---|---|
| No | Yes | Yes | Yes | No |
*Heated because of the low temperature of the hot spring source
*Circulated to maintain the bathing temperature and protect the hot spring resource
*A solid chlorine disinfectant is added once a day after check-out
Mountain Open-Air Bath “Fukayu”
True to its name, this bath reaches a maximum depth of 130 cm, making it exceptionally deep. The bottom of the bath is lined with stones, so guests bathe while standing. This unique design allows you to enjoy the hot spring while the stones gently stimulate the pressure points on the soles of your feet.
Skin Feeling Gauge
Ideal for:
People interested in skin-beautifying effects
People with dry skin
People with minor cuts
People looking to relax and relieve stress
People sensitive to cold
People who enjoy a refreshing post-bath feeling
Indications by Spring Quality
(for bathing)
Cuts
Peripheral circulatory disturbance
Sensitivity to cold
Depression
Dry skin
General Indications (for bathing)
Chronic pains or stiffness of muscles or joints (chronic phase of rheumatoid arthritis, osteoarthritis, lower back pains, nerve pains, frozen shoulder, bruises, sprains, etc.), Muscle stiffness in motor paralysis, Sensitivity to cold, Peripheral circulatory disturbance, Gastrointestinal hypofunction (slow digestion, intestinal gas formation, etc.) Mild hypertension, Impaired glucose tolerance (diabetes), Mild hypercholesterolemia, Mild asthma or Emphysema, Hemorrhoidal pains, Autonomic instability, Various symptoms from stress (sleep disorders, depression, etc.), Restorative phase from illness, Recovery from fatigue, Health promotions
General Contraindications (for bathing)
Active stage of diseases (especially when fever is accompanied), Active tuberculosis, Advanced
malignant tumor or the case of significant debility involving severe anemia, Severe cardiac or lung
diseases involving suffocation feelings with a little movement, Severe kidney diseases involving
edema, Gastrointestinal bleeding, When bleeding is visible, Acute exacerbation stage of chronic
diseases
*There are no general indications or contraindications for drinking.
Onsen Power Chart
→Circulation and Filtration system
■ Circulation and Filtration system・・・Hot spring water from the property's private hot spring source is circulated through a hair catcher, filtration system, and disinfection system before being heated to the proper bathing temperature and returned to the baths. Fresh hot spring water is continuously added while impurities and debris are removed, helping to keep the bathwater clean and hygienic.
Mountain Indoor Bath “Fukayu”
The indoor bath at “Fukayu” offers a calm and relaxing atmosphere. After enjoying the deep standing bath in the open-air section, it is the perfect place to unwind and soak at a leisurely pace. The bath features a wooden rim and a stone-lined tub, creating a warm, traditional ambiance.
Keywords of this Onsen
Officially classified as
Sodium–Chloride cold mineral springs,
yet it contains over 1,000 mg/kg of hydrogen carbonate ions!
↓
With over 1,000 mg/kg,
it qualifies as a therapeutic hot spring on its own.
However, due to the official naming rules
(only 20% or more components are listed),
another spring type is hidden within
its official classification!
↓
Known as “Hot springs for warmth”
and “Hot springs for cuts”,
it also turns out to be “Hot springs for beautiful skin” (Hydrogen carbonate cold mineral springs)!
In other words, this is a Triple Spring Type, combining the Sodium ions × Chloride ions pairing (Sodium–Chloride cold mineral springs) and the Sodium ions × Hydrogen carbonate ions pairing (Hydrogen carbonate cold mineral springs), offering the benefits of “Hot springs for warmth”, “Hot springs for cuts”, and “Hot springs for beautiful skin”.
*In Japan, springs with a source temperature below 25°C are officially classified as a Cold mineral spring rather than Hot spring.
Incidentally, both Hot spring and Cold mineral spring belongs to the broader category of Mineral spring.
In this case, imagine the spring as a story. The Sodium ion is the central character, while Chloride ions and Hydrogen carbonate ions are two partners competing to pair with it.
Or, if you prefer a movie analogy: The Sodium–Chloride cold mineral springs play the leading role, while the Hydrogen carbonate cold mineral springs play an important supporting role.
Hot springs contain both cations and anions, which always exist in pairs. Thinking of each cation–anion pair as a team that determines the spring's characteristics makes a hot spring analysis report much easier for first-time readers to understand.
The official spring classification of this spring water is Sodium–Chloride cold mineral springs (Weakly Alkaline, pH 7.9 / Spring temperature: 15°C). When classified as Chloride springs, the Indications for bathing include Cuts, Peripheral circulatory disturbance, Sensitivity to cold, Depression, and Dry skin.
However, this spring also has another, less obvious character as Sodium–Hydrogen carbonate cold mineral springs. When classified as a hydrogen carbonate spring, the indications for bathing include Cuts, Peripheral circulatory disturbance, Sensitivity to cold, and Dry skin. Unlike Chloride springs, Depression is not listed as Indication for Hydrogen arbonate springs.
Based on current knowledge in balneology (the study of the therapeutic effects of hot springs), this may explain why Depression is not listed as Indication for Hydrogen carbonate springs.
One possible reason is that improving Depression is believed to depend largely on activating the parasympathetic nervous system, which calms an overactive nervous system and promotes both physical and mental relaxation.
Chloride springs are known for their strong heat-retaining effect, produced by chloride ions. By keeping the body warm for longer, they are thought to promote parasympathetic activity and encourage a more relaxed state.
In contrast, Hydrogen carbonate springs wash away excess sebum from the skin with the help of hydrogen carbonate ions. After bathing, this allows body heat to dissipate more easily from the skin, leaving a refreshing feeling. For this reason, Hydrogen carbonate springs are often referred to as “Hot springs for refreshing (with cooling effect)”.
Rather than promoting deep relaxation, this refreshing effect may help increase alertness by favoring sympathetic nervous system activity. This may be one possible reason why Depression is not listed as Indication for hydrogen carbonate springs.
On the other hand, some may question why Hydrogen carbonate springs—often referred to as “Hot springs for refreshing (with cooling effect)”—are also indicated for Peripheral circulatory disturbance and Sensitivity to cold. At first glance, this may seem contradictory.
One possible explanation is that Hydrogen carbonate springs also improve blood circulation, although not as strongly as Chloride springs.
Unlike Chloride springs, which help retain body heat by forming a salt film that reduces heat loss through the sweat glands, Hydrogen carbonate springs are thought to work in a different way. Hydrogen carbonate ions are believed to act on the skin, promoting peripheral blood circulation and making it easier for blood to reach the hands and feet. This may help improve Peripheral circulatory disturbance and relieve Sensitivity to cold.
Mountain Open-Air Bath “Ishiyu”
Rankeisou offers two private open-air baths: “Fukayu” and “Ishiyu”. True to its name, “Ishiyu” features a stone-built bath surrounded by lush greenery, creating a rustic atmosphere where guests can fully immerse themselves in nature.
Onsen Classification
️Hot springs are classified not only by their spring quality, but also by three additional factors: osmotic pressure, hydrogen ion concentration (pH level), and spring temperature.
Osmotic Pressure
(Isotonic, Weakly Alkaline, Cold mineral spring)
In hot spring classification, “osmotic pressure” refers to comparing the concentration of dissolved components in the spring water (mainly salts) with that of human body fluids (such as blood and intracellular fluid). Based on this comparison, springs are categorized as hypotonic, isotonic, or hypertonic. The difference in concentration serves as an indicator of how easily water moves between the hot spring water and body fluids.
Total Dissolved Substances
8,739 mg/kg
Classified as a Isotonic spring
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Isotonic Total Dissolved Substances 8,000 mg/kg or more to less than 10,000 mg/kg 👤 Body fluid concentration ≒ ♨ Onsen concentration Water・・・Hardly moves into or out of the body Onsen components・・・Minimally absorbed and act gently on the body Isotonic means having the same osmotic pressure as human body fluids. It is equivalent to a saline solution made by dissolving approximately 8.8 g of salt in 1 liter of water. Because its concentration is close to that of body fluids, there is little movement of water or onsen components due to osmotic pressure. As a result, it is considered to place the least strain on the body and to be the gentlest in terms of stimulation. |
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Hypertonic Total Dissolved Substances 10,000 mg/kg or more 👤Body fluid concentration ＜ ♨ Onsen concentration Water・・・Easily moves out of the body Onsen components・・・Easily absorbed into the body Because its osmotic pressure is higher than that of human body fluids (isotonic fluids), water tends to move out of the body more easily, while onsen components are more readily absorbed into the body. As a result, stronger therapeutic effects may be expected. However, hypertonic hot springs are also more likely to cause “hot spring fatigue (yu-atari)” and can be more physically demanding. They are generally regarded as “rich or highly concentrated hot springs”. Among Japanese hot springs, hypertonic springs are relatively uncommon, and a comparatively large proportion are classified as mineral springs (below 25°C) rather than hot springs (25°C or higher). |
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Hydrogen Ion Concentration
(Isotonic, Weakly Alkaline, Cold mineral spring)
In the hot spring analysis report, the section titled “Examination and test results at gushing location” includes the listed pH value. Chemically, a pH of 7.0 is considered neutral; values below this are acidic, and values above it are alkaline. According to the “Guidelines for the Mineral Spring Analysis Methods”, the chemical nature of a mineral spring is classified based on its pH value at the time of emergence, as shown in the table below.
pH 7.9
Classified as Weakly Alkaline
Spring Temperature
(Isotonic, Weakly Alkaline, Cold mineral spring)
15.0℃
Classified as Cold mineral spring
Under the “Hot Springs Act”, water that contains one or more designated substances at or above the legally specified levels and has a source temperature of 25°C or higher is classified as a “hot spring”. If the temperature is below 25°C, it is labeled a “mineral spring”. Furthermore, as noted above, hot springs are classified by source temperature as high-temperature spring, hot spring, or low-temperature spring.
Large Public Baths “Maki-no-Yu”
The “Maki-no-Yu” public bath features both an indoor bath and an open-air bath, each provided separately for men and women. The abundant mineral deposits visible around the baths reflect the rich mineral content of Rankeisou's spring water. Incidentally, “Maki” is a local place name that refers to the uppermost area of this region.
Summary
Rankeisou's hot spring is a rare, high-mineral Isotonic Sodium–Chloride cold mineral springs containing 8,739 mg/kg of dissolved substances (excluding gaseous). Such a high mineral concentration is uncommon among isotonic springs in Japan.
The chloride-rich water forms a protective salt film on the skin, helping to reduce heat loss. This is why it is known “Hot springs for warmth” and “Hot springs for cuts”. It provides excellent heat retention, moisturizing, and bactericidal properties, which may help relieve Sensitivity to cold and Dry skin.
In addition, despite its official classification, the spring contains an impressive 1,191 mg/kg of Hydrogen carbonate ions, together with a Weakly Alkaline pH of 7.9. These characteristics provide the gentle cleansing effect and smooth skin feel for which Hydrogen carbonate springs—often called “Hot springs for beautiful skin”—are well known.
Rich in minerals yet remarkably gentle on the skin, Rankeisou's hot spring offers a rare combination of “Triple Spring Type” in a single source.
Facility Data
| Founded in | 1927 (Showa 2) |
|---|---|
| Check in | 4:00 PM |
| Check out | 10:00 AM |
| Location | Mountain, River, Garden |
| Rooms | Total 16 rooms |
| Capacity | 60 people |
| Parking | 50 cars |
| Facilities | Gift shop, Table tennis, Japanese garden with waterwheel |
| Internet | Wi-Fi available |
| Barrier-free | Some supported |
| Bidet toilet | Equipped |
Keywords for this inn
| Cold mineral spring with therapeutic salt content |
| Enjoy a peaceful countryside setting with a stream and waterwheel |
| Savor traditional satoyama cuisine inspired by rural Japan |
| Open-air baths where you can feel at one with nature |
| A hidden hot spring retreat with unique charms in every season |
Hot Spring (Onsen) Report
| The spring quality of Rankeisou is classified as Sodium - Chloride cold mineral springs. Its main components are Sodium Ions (cations) and Chloride Ions (anions). This spring type is commonly known in Japan as a “Hot springs for warmth”. The salt contained in the hot spring water adheres to the skin, forming a thin・・・ Read more → |
Transportation Access
| By Train | The nearest stations are Tsubame-Sanjo Station (approximately 2 hours from Tokyo Station by Joetsu Shinkansen) and Higashi-Sanjo Station (approximately 7 minutes from Tsubame-Sanjo Station via the JR Yahiko Line) |
|---|---|
| By car | Approximately 23.4 km from the Sanjo-Tsubame Interchange (IC) on the Hokuriku Expressway via local roads |
| Shuttle Bus | Complimentary shuttle service is available to and from Tsubame-Sanjo Station and Higashi-Sanjo Station (reservation required) |
| Address | Niigata／Echigo-Nagano Onsen／Echigo-Nagano Onsen RANKEISOU 1450 Nagano, Sanjo City, Niigata 955-0132, JAPAN TEL:+81-(0)256-47-2211 |