BETTEI SENJUAN

At Bettei Senjuan in Tanigawa Onsen, Gunma Prefecture, three private hot spring sources are blended for use.
These sources are called “Kuraoki-no-Yu,” “Kajika-no-Yu,” and “Senju-no-Yu,” and the mixing ratio is 5:8:12.
The discharge volume and temperature of each source are as follows:
Kuraoki-no-Yu: 180 L/min, 35℃
Kajika-no-Yu: 60 L/min, 50℃
Senju-no-Yu: 120 L/min, 43℃
The standard temperature for each bathtub is set at 41.4℃, but this is adjusted by modifying the blending ratio according to the outdoor temperature, without adding water.
In winter, the water may be heated to keep it at a suitable bathing temperature, though heating has far less impact on spring quality than water addition. All sources are mechanically drawn, meaning they are extracted by drilling deep boreholes.
Although each spring has a different temperature, by blending them, the water is supplied to all baths at the optimum temperature in a 100% free-flowing system (gensen kakenagashi).

Gensen kakenagashi refers to a system where hot spring water flows directly from the source into the bathtub, and the excess water simply overflows into the drain and is discarded.
This is considered a luxurious use of hot spring water, but it is also regarded as the most effective system for maximizing the natural benefits of the spring.
The total discharge volume from the three private sources is approximately 360 liters per minute. With a maximum guest capacity of 50 at Bettei Senjuan, this allows for an estimated 7.2 liters per person per minute. It is said that, to enjoy a hygienic gensen kakenagashi system, approximately 1 liter of hot spring water per minute per person is required. If the discharge volume does not meet this level, a circulation and filtration system with chlorine disinfection is usually needed. At this inn, the available spring volume far exceeds the standard, even numerically.

The spring quality is classified as “Calcium, Sodium – Sulfate, Chloride Springs” (Hypotonic, Weak alkaline, Hot spring). According to the former classification system, it was referred to as a “Salt-containing Gypsum Spring”. The total amount of dissolved substances, excluding gaseous components, is 1,293 mg/kg. Many hot spring inns around Tanigawa Onsen are classified as so-called simple springs, with total dissolved substances of less than 1,000 mg/kg. Compared to those, the hot spring at this inn is a colorless and clear water with no peculiar smell or taste, but the content is quite “dense”, qualifying it as a rich and therapeutic hot spring.
The inn has a total of 18 guest rooms, and all rooms are equipped with open-air baths where guests can enjoy seasonal views throughout the year. In addition to the private baths, there are two gender-separated public baths, “Ichinokura” and “Sennokura”, each featuring an indoor bath and an open-air bath named “Suzumushi-no-Yu” and “Hotaru-no-Yu” respectively.
While the size of each bath varies, a total of 22 bathtubs are supplied with 100% free-flowing hot spring water.
Compared to many inns that struggle to secure enough hot spring water, this is surely an enviable condition.

The primary characteristic of this hot spring is the combination of calcium ions (cations) and sulfate ions (anions), forming a “Calcium–Sulfate Spring”. Calcium ions help regulate the contraction and dilation of blood vessels, have a calming effect on the nervous system, and relieve pain and inflammation. They also contribute to promoting skin regeneration.
Sulfate ions have bactericidal properties, making them effective for treating minor cuts. Sulfate springs are often referred to as “Hot springs for cuts”. In addition, these ions help dilate blood vessels and increase oxygen delivery in the bloodstream, which is why they are also known as “Hot springs for stroke prevention”. By promoting blood circulation, they can help with sensitivity to cold and peripheral circulatory disturbances. These warming effects also support the regulation of the autonomic nervous system and may help alleviate depression. Sulfate ions also have a moisturizing effect on dry skin, making them effective for dry skin conditions. When combined with calcium ions, this becomes a “Calcium–Sulfate Spring”, which was traditionally referred to as a “Gypsum Spring”. Calcium ions support the formation and renewal of the stratum corneum, while sulfate ions enhance skin elasticity and help prevent wrinkles. As such, “Calcium–Sulfate Springs” are considered one type of “Hot spring for beautiful skin".

The second key component of this spring is the combination of sodium ions (Na⁺) and chloride ions (Cl⁻), forming a “Sodium–Chloride Spring”.
Sodium ions, which are cations, act on the stratum corneum of the skin and provide moisturizing effects.
They help the skin retain moisture, making them beneficial for improving dry skin conditions.
Sodium ions are also known to relax muscle tension and relieve joint and muscle pain, making them suitable for fatigue recovery and easing symptoms of rheumatism. Furthermore, through osmotic effects, they promote blood circulation and enhance metabolism, which can contribute to improving sensitivity to cold and supporting detoxification. Bathing in sodium-rich hot springs also enhances the overall relaxation effect, aiding recovery from fatigue. In addition, sodium ions help remove dirt and waste from the skin, keeping it clean.
When combined with chloride ions, they become a “Sodium–Chloride Spring”, which forms a salt film on the surface of the skin. This contributes to preventing dry skin by maintaining moisture, and the salt pack helps block sweat glands, thereby enhancing heat retention. For this reason, it is also referred to as a “Hot spring for warmth”.
Its sustained warming effect is considered effective for peripheral circulatory disturbances and sensitivity to cold. By helping to stabilise the autonomic nervous system, it may also bring a sense of mental calm.
The increase in body temperature suppresses the secretion of stress hormones, potentially improving mood and proving beneficial for depression.
Additionally, due to its bactericidal effects, it promotes the healing of skin inflammation and minor cuts, earning it the nickname “Hot spring for cuts”.
Chloride springs are often referred to as “Hot springs for finishing touch.” This is because, after bathing in so-called “Hot springs for beautiful skin” — such as weak alkaline simple springs, which help remove dead skin cells, and hydrogen carbonate, sulfate, or sulfur springs — entering a chloride spring provides salt coating & moisturizing effects that help seal in the beneficial components absorbed from the previous bath and maintain skin hydration. The hot spring at Bettei Senjuan is also characterised by its pH of 8.4, classifying it as Weak Alkaline.
Since human skin is generally mildly acidic, bathing in weak alkaline water causes a slight reaction on the skin’s surface, resulting in a smooth and silky texture.This sensation occurs because the weak alkalinity gently dissolves old keratin layers on the skin.　After bathing, one will notice the skin feels noticeably smoother and softer.
The combination of sulfate springs with anti-aging properties that may help prevent wrinkles and promote skin rejuvenation, weak alkaline hot springs that gently remove dead skin cells to leave the skin smooth and silky, and chloride springs that offer salt-based coating and moisturizing effects, clearly qualifies the hot spring at Bettei Senjuan as a “Hot spring for beautiful skin”.

In addition to the major cations and anions, attention should also be paid to the non-dissociated components.
Metasilicic acid (H₂SiO₃), often referred to as a natural moisturizing substance, is present at 43.6 mg/kg.
Although it does not reach the threshold of 50 mg/kg required to officially qualify as a hot spring component, it is still sufficient to provide notable effects. When present at 100 mg/kg or more, it is considered—though in a secondary sense—as one of the criteria for being called a “Hot spring for beautiful skin”.

Metaboric acid (HBO₂) is also contained in a relatively high amount—10.6 mg/kg.
This exceeds twice the minimum requirement of 5 mg/kg for qualifying as a hot spring component.
Metaboric acid is known for its cleansing effects and is said to be effective in preventing acne. When it reaches 10 mg/kg or more, it is regarded—albeit in a supplementary capacity—as one of the indicators for being called a “Hot spring for beautiful skin”.

The explanation so far has focused primarily on the chemical properties and therapeutic effects of the hot spring.
However, the benefits of a hot spring experience go far beyond its components alone.
At Bettei Senjuan, guests can enjoy open-air baths with superior spring quality while being surrounded by the changing beauty of the seasons.
Located in a serene mountain valley at the foot of Mount Tanigawa, one of Japan’s 100 famous mountains, the environment offers fresh, clean air and breathtaking scenery.
Soaking in these natural hot springs not only soothes the body, but also contributes significantly to mental and emotional well-being.
Although a hot spring is not a medicine, it can gently help correct imbalances in the mind and body from a different approach.
In that sense, a stay at Bettei Senjuan is more than just bathing—it is an experience of restoration and renewal, both physically and spiritually.

Tanigawa Onsen is located on the border between Gunma and Niigata prefectures, amidst a mountain stream and forest filled with negative ions, with a view of the famous Mt. Tanigawadake (altitude 1977m). Tanigawa Onsen is a relatively small hot spring area, but it seems to attract many travelers because of its one of a kind atmosphere and nature-rich environment. Tanigawa Onsen is said to have opened around 1400. There are records that literary figures and artists such as Osamu Dazai, Makisui Wakayama, and Yasunari Kawabata visited the area during the Taisho and early Showa eras. The "Bettei Senjuan" opened in 1997 as an annex of Ryokan Tanigawa on a vast site of 8,000 tsubo (about 6.5 Acres), which has now been expanded with the purchase of additional land to 20,000 tsubo (about 16 Acres). At the time, there were several inns in Japan offering guest rooms with open-air baths, but Senjuan may have been the first inn to offer open-air baths in every room. In 2012, the hotel was approved to join Relais & Chateaux, a prestigious hotel and restaurant group based in France. To become a member, a hotel or restaurant is subject to a strict "5C" assessment: Courtesy (heartfelt hospitality), Charm (refined and attractive space), Character (distinctive and individual style), Calm (calm and relaxing atmosphere), and Cuisine (high quality cuisine). Only a few hotels and lodging facilities in Japan have been approved to join Relais & Chateaux, and one of them is "Bettei Senjuan". The "Bettei Senjuan" has continued to thrive since its opening. This is probably due to the fact that the facilities are continually evolving and repeat customers keep coming back. A reading room was built in 1998, and dining rooms were added in 2000, 2006, and 2008. In 2004, an esthetic salon and footbath were opened. In 2008, a garden terrace with a hand bath was opened. The company is planning to hold events using the garden terrace and spacious courtyard to unite with nature, and we can look forward to its further evolution. The high level of not only the tangible aspect but also the intangible aspect of "hospitality" can be felt from many of the staff members. Under the leadership of Hidehiro Kubo, the president of the inn, the spirit to create a good facility can be felt. An inn that improves its intangible aspects in parallel with the tangible aspects of its facilities will also have a high level of customer satisfaction. The customers who frequent this facility may be more accurately described as supporters than repeaters. Spending time in a luxurious space in a quiet mountain setting is the happiest moment for a human being. It is a wise choice to spend a blissful time at the "Bettei Senjuan".