Spring Type


On the Hot Spring Classification page the temperature, pH and osmotic pressure are discussed, but spring type is probably the most important while also the most obtuse of these classifications. In Japan the types of springs are determined by the national law which was reformed in 1979, however you will still see the old types still being used or mentioned as some feel they are easier to understand. There are a few major types that have many subcategories and heavily nuanced crossover. I have decided to only list the major categories in the reviews on this site for ease of understanding. In the categories below some of the more common subcategories are listed.

Simple Hot Spring 単純温泉

Simple Alkaline Hot Spring アルカリ単純温泉

These are hot springs that do not contain enough minerals to be classified in detail but are still considered natural hot springs. This category includes some of the very famous springs in Japan such as Gero and Dogo. If you go to a supersento that has a natural spring, it is likely to be a simple spring. Being a simple spring does not necessarily mean it is a poor or not enjoyable spring. Due to the pH or some other unknown factor, some of my favorite baths have been simple springs. Generally they are gentle thanks to the low mineral content and soft feeling on the skin with no smell or color to the water. The alkaline simple springs can give you a smooth, slippery feel.

Subcategory Examples:

  • Simple hot spring / 単純温泉

  • Springs that are neutral to pH8.5

  • Simple alkaline hot spring / アルカリ性単純温泉

  • Springs that are pH8.5 or higher

Representative Hot Spring:

  • Dogo Onsen / 道後温泉

  • Gero Onsen / 下呂温泉

Yamabato-yu - Nara - Chloride Spring

Chloride Spring 塩化物泉

These springs have salt as the primary component and are the most common type of hot spring in Japan. 1kg of spring water must contain at least 1,000 mg of dissolved chloride salts to get this classification. The salt content helps the body retain heat while limiting perspiration. It is believed because you lose less liquid in your body due to perspiration while in the bath, it is more difficult to suffer from overexposure to the heat. Bath salts are called that because they basically contain salt as the active ingredient and provide a similar effect. Other elements as seen in the subcategories below also be found in the water so the color and smell can differ greatly between springs. While salt baths are thought to be helpful for abrasions, very strong salt baths can make your skin itch or cause pain.

Subcategory Examples:

  • Sodium chloride spring / ナトリウム−塩化物泉

  • Strong sodium chloride spring / ナトリウム−塩化物強塩泉

  • Bicarbonate, sodium chloride spring / ナトリウム−塩化物・炭酸水素塩泉

  • Sulfate, sodium chloride spring / ナトリウム−塩化物・硫酸塩泉

  • Sulfate, bicarbonate, sodium chloride spring / ナトリウム-塩化物・硫酸塩・炭酸水素塩泉

  • Sodium chloride spring with carbon dioxide / 含二酸化炭素-ナトリウム-塩化物泉*

*These types of springs will be classified as a Carbon Dioxide Spring - 二酸化炭素泉 in the reviews.

Representative Hot Springs:

  • Kaike Onsen / 皆生温泉

  • Kinosaki Onsen / 城崎温泉

Bicarbonate Spring 炭酸水素塩泉

These springs have a primary component of bicarbonate with over 1,000 mg dissolved in each kilogram of spring water. Alkaline types feel very smooth on the skin and are called “Bijin no Yu” [美人の湯] as they are thought to promote beautiful skin. These springs can be clear to shades between brown and brownish yellow. Some of these springs can be so smooth on the skin it feels oily or soapy while in the water while others which have more calcium feel dry or chalky on the body and leave sediment on any surface it interacts with.

Subcategory Examples:

  • Sodium bicarbonate spring / ナトリウム-炭酸水素塩泉

  • Sodium chloride, sodium bicarbonate spring / ナトリウム-炭酸水素塩・塩化物泉

  • Sulfate, bicarbonate spring / ナトリウム-炭酸水素塩・硫酸塩泉

  • Sodium chloride, sulfate, bicarbonate spring / ナトリウム-炭酸水素塩・塩化物・硫酸塩泉

  • Calcium (and/or magnesium), bicarbonate spring / カルシウム(・マグネシウム)-炭酸水素塩泉

Representative Hot Springs:

  • Arima Onsen / 有馬温泉 (silver spring / 銀線)

  • Ureshino Onsen / 嬉野温泉

Izutsuya - Yumura Onsen, Hyogo - Hydrogen Sulfate Spring

Hydrogen Sulfate Spring 硫酸塩泉

At least 1,000 mg of sulfate is diluted in each 1kg of spring water. These are clear springs with no color and a bitter taste. In fact, drinking from these springs is said to help fight liver disease, lower blood pressure and constipation. Please check the local information before drinking from any spring as the quality can fluctuate greatly. Bathing in these springs is recommended for people with dry skin.

Subcategory Examples:

  • Sodium hydrogen sulfate spring / ナトリウム-硫酸塩泉

  • Calcium hydrogen sulfate spring / カルシウム−硫酸塩泉

  • Magnesium hydrogen sulfate spring / マグネシウム-硫酸塩泉

  • Sodium chloride, sodium hydrogen sulfate spring / ナトリウム−硫酸塩・塩化物泉

  • Sodium chloride, calcium, sodium hydrogen sulfate spring / カルシウム・ナトリウム-硫酸塩・塩化物泉

  • Sodium chloride, magnesium, sodium hydrogen sulfate spring / マグネシウム・ナトリウム-硫酸塩・塩化物泉

Representative Hot Spring:

  • Matsue Shinjiko Onsen / 松江しんじ湖温泉

  • Yumura Onsen / 湯村温泉

Carbon Dioxide Spring 二酸化炭素泉

These springs have at least 1,000 mg of dissolved carbon dioxide gas per each 1kg of spring water. There are only a few of these naturally occurring in Japan. The major one that I know of is Yokatan in Miki, and even that spring is classified as a chloride spring with carbon dioxide. The gensen [源泉/straight from the well] bath there will give off a large amount of carbon dioxide gas that you will inhale as you bathe. This will give you a mild lightheadedness and sedative effect as you are starving yourself of oxygen so bathing here can be very calming but you need to take breaks and get away from the spring every 15 minutes at least. Carbon dioxide springs when heated up will expel their dissolved gasses. However when used at 38°C or cooler the springs will have a large amount of carbon dioxide dissolved into the water. Soon after sitting in one of these baths your skin will be covered by small bubbles of gas. It is like bathing in a bottle of soda water. These baths and their more common artificial counterparts will leave the skin feeling warm even if the temperature of the bath is low. Bathing in them helps expands the capillaries bringing warm blood to the edges of your skin. This also has the effect of lowering blood pressure.

Subcategory Examples:

  • Simple carbon dioxide spring / 単純二酸化炭素泉

Representative Hot Springs:

  • Arima Onsen / 有馬温泉

  • Beppu Onsen / 別府温泉

Acidic Spring 酸性泉

These springs can be very powerful. To be classified as acidic there needs to be at least 1,000 mg of hydrogen in each 1kg of spring water. They are sour to the taste and are typically clear or slightly yellow. If you have weak skin, you should be careful bathing in them and it is recommended that you rinse off with fresh water after soaking in these baths. Upon entering some people do experience a tingling sensation. These springs have a strong antibiotic power and are good at fighting eczema and even fungal infections like athletes' feet.

Subcategory Examples:

  • Simple acidic spring / 単純酸性泉

Representative Hot Spring:

  • Beppu Onsen / 別府温泉 (Hoyoland / 保養ランド)

Unzen Onsen, Nagasaki - Sulfur Spring

Sulfur Spring 硫黄泉

These springs have to have at least 2mg of sulfur containing compounds for every 1kg of spring water. They can be clear, to cloudy white and even green. Sulfur springs are often presented as the example of banelogy and hot spring classification as they are the easiest to detect to the casual bather. Unlike some of the other spring types you will 100% know that you are at a sulfur spring from the unmistakable smell. More than often the post bath body feel will also give you that understanding. Like carbon dioxide springs, these springs promote the dilation of the blood vessels heating the body and increasing blood flow. The sulfur helps relieve skin diseases like eczema, atopic dermatitis among other positive effects. Japan is also blessed in having many sulfur springs compared to other countries.

Subcategory Examples:

  • Simple sulfur spring / 単純硫黄泉

  • Sodium chloride spring with sulfur / 含硫黄−ナトリウム−塩化物

  • Bicarbonate, sodium chloride spring with sulfur / 含硫黄−ナトリウム−塩化物・炭酸水素塩泉

  • Simple sulfur spring (hydrogen sulfide type) / 単純硫黄泉(硫化水素型)

  • Sodium chloride spring with sulfur (hydrogen sulfide type) / 含硫黄−ナトリウム−塩化物(硫化水素型)

  • Acidic, sulfur (and sodium) hydrogen sulfate spring (hydrogen sulfide type) / 酸性・含硫黄(−ナトリウム)− 硫酸塩泉(硫化水素型)

Representative Hot Spring:

  • Beppu Onsen / 別府温泉

  • Unzen Onsen / 雲仙温泉

Chalybeate (Iron) Spring 含鉄泉

Chalybeate is a word meaning springs that have iron salts in them. These springs will have 20 mg or more dissolved iron in each 1kg of spring water. Although these springs are clear when they emerge from the earth, the iron in them will oxidize and turn a brownish color. In Europe and North America there is a history of bathing and drinking chalybeate spring water and even many cities named Chalybeate. In particular bathing and drinking Chalybeate spring water is good for anemia and menstrual issues in women.

Subcategory Examples:

  • Chalybeate bicarbonate spring / 鉄−炭酸水素塩泉

  • Acidic chalybeate sulfuric acid spring / 酸性−鉄−硫酸塩泉

  • Sodium, chalybeate bicarbonate spring / ナトリウム・鉄(II)-炭酸水素塩泉

Representative Hot Spring:

  • Arima Onsen / 有馬温泉 (gold spring / 金線)

Some springs do not provide a spring report or keep that information obtuse.

Kawaburo - Misasa Onsen, Tottori - Radioactive Spring

Radioactive Spring 放射能泉

Each kg of water has to contain at least 3 nanocurie units (30×10-10) of radon. The radon is absorbed into the body through the skin and breathed in as the gas escapes from the water. The use of radioactivity for positive medical effects is greatly debated to this day, but has a long history in Europe and North America since the discovery of radiation. Radon caves where people go to breathe in naturally occurring radon gas for therapeutic reasons are still in operation in parts of North America. It is claimed that bathing in these springs is good for combating gout and atherosclerosis among other things. Radioactive springs are also used purely for pleasure. These springs are typically colorless and can be very slippery or soapy to the touch. While the radioactive exposure one would get is much less than a typical x-ray, one should use their own judgment when deciding to expose themselves to radioactivity.

Subcategory Examples:

  • Simple radioactive spring / 単純放射能泉

  • Simple weak radioactive spring / 単純弱放射能泉

Representative Hot Spring:

  • Misasa Onsen / 三朝温泉

Other Spring Types - その他温泉

These types are listed in the law but seem to be very rare in Japan.

  • Aluminum Spring 含アルミニウム泉

These springs have a disinfectant effect and are good against skin diseases. Removed from the official classification in 2014.
  • Copper-Chalybeate Spring 含銅-鉄泉

Good for anemia and menstrual issues in women. They are typically reddish brown in color. Removed from the official classification in 2014.
  • Iodine Spring 含よう素泉

Drinking this spring is thought to be good against high cholesterol. They are brown or black in color. Added to the official classification in 2014.

Unclassified spring - 温泉法上の温泉

Some springs do not provide a spring report or keep that information obtuse.

References - 参照文献