What is a simple hot spring? Learn the Ministry of the Environment 기준: less than 1,000 mg/kg dissolved substances and spring water at 25°C or above. Also see why it is not simply weak water, its clear and gentle character, its link to alkaline simple hot springs with pH 8.5+, and bathing cautions.
Published: Dec 23, 2025
What is a simple hot spring? Learn the Ministry of the Environment 기준: less than 1,000 mg/kg dissolved substances and spring water at 25°C or above. Also see why it is not simply weak water, its clear and gentle character, its link to alkaline simple hot springs with pH 8.5+, and bathing cautions.
Published: Dec 23, 2025
A simple hot spring is one of the 10 types of therapeutic springs. It is a spring type in which the dissolved components in the hot spring water do not reach the standard amount required for a specific spring classification. Under the Ministry of the Environment’s criteria, it refers to water with less than 1,000 mg of dissolved substances (excluding gaseous ones) per 1 kg of hot spring water and a spring temperature of 25°C or higher. Because it has the word simple in its name, it is often misunderstood as weak in minerals, but this is only a classification label and does not mean the water is thin or low in value.
In short, simple hot springs are often nearly colorless, clear, tasteless, and odorless, with gentle stimulation that makes them easy to enter. For that reason, they are often suitable for onsen beginners, people who want to avoid long soaking, and families. On the other hand, they may feel understated to those seeking a strong character. This article explains the definition of simple hot springs, their features, their relationship with alkaline simple hot springs with high pH, and their position among other spring types, based on the Ministry of the Environment’s criteria. For the full picture of all 10 therapeutic spring types, see the Onsen Spring Types Guide; here, we focus only on simple hot springs.
This article provides general information and does not guarantee any specific therapeutic or beauty effects. If you have a chronic condition, are under treatment, or are not feeling well, do not push yourself and follow your doctor’s advice and the facility’s guidance.
Whether a spring is classified as a simple hot spring is determined by the amount of dissolved components in the water and the spring temperature. In the Ministry of the Environment’s Guidelines for Mineral Spring Analysis, simple hot springs are defined among therapeutic springs as water with less than 1,000 mg of dissolved substances per 1 kg of hot spring water, excluding gaseous substances, and a spring temperature of 25°C or higher. If a bathhouse displays labels such as simple hot spring or alkaline simple hot spring, the water meets this standard.
A common misunderstanding is that simple means weak in minerals. Simple hot springs do contain various dissolved components. However, sodium, sulfate ions, and other components have not reached the prescribed amount needed to be classified as a specific spring type such as chloride spring or sulfate spring. In other words, the name simple hot spring is just a classification, not a statement that the water is thin or less valuable. Put differently, it is a balanced spring without an outstanding main component, not water with little total mineral content.
| Item | Details |
|---|---|
| Dissolved substances, excluding gases | Less than 1,000 mg per 1 kg of hot spring water |
| Spring temperature | 25°C or higher |
| Appearance and smell | Often nearly colorless, tasteless, and odorless |
| Alkaline simple hot spring | The above plus pH 8.5 or higher |
If the dissolved substances are 1,000 mg or more, or if a specific component exceeds the prescribed amount, the spring is not classified as a simple hot spring and instead becomes a chloride spring, sulfate spring, or bicarbonate spring, among others. The definition of hot springs themselves, such as the minimum standards for temperature and components, is separate from the definition of simple hot springs, so reading What Is an Onsen? as well can make it easier to understand where a hot spring begins and where a therapeutic spring begins.
Simple hot springs tend not to have a strong visual or aromatic character. They lack obvious markers such as the cloudy white appearance of sulfur springs or the reddish-brown color of iron-rich springs, and they are often colorless, clear, and only gently scented. Some people may feel disappointed if they expect a strongly distinctive onsen, but many others appreciate this calmness for the sense of comfort it brings.
Because they are considered relatively mild, they are a good match for people who are not used to hot springs, people who want to avoid long soaking, or situations where they want to bathe comfortably while monitoring their condition. They are also easy to choose for family trips where people of different ages are bathing together. That said, even if the water feels gentle, facilities with high water temperatures can warm the body more than expected, so it is safer to start with a short soak rather than staying in too long.
Rather than focusing on mineral character, it is easier to understand simple hot springs as springs that let you enjoy the comfort of bathing itself and the slow, relaxing time spent in a hot spring resort.
Among simple hot springs, those with a high pH are called alkaline simple hot springs. In general, this refers to water with a pH of 8.5 or higher, and bath signs often distinguish them with the label alkaline simple hot spring.
Alkaline water is said to soften the outer layer of the skin, and during or after bathing you may feel that your skin becomes smooth and slippery. Because of this texture, some hot spring resorts are introduced as beauty baths, but this is only a traditional nickname based on how the skin feels, not a guarantee of cosmetic benefits. Experiences vary from person to person, and this article does not make definitive claims about effects. For more on the relationship between pH and skin feel, and how to tell alkaline springs from acidic ones, see the Onsen pH Guide.
One important point is that not all simple hot springs have the same feel. Even within the simple hot spring category, pH and mineral composition vary, and waters that are close to neutral do not create the same smooth sensation as alkaline simple hot springs. Even if two springs are both called simple hot springs, the impression can differ greatly from one source to another.
The position of a simple hot spring lies in the fact that it does not have one outstanding main component. When compared with chloride springs or sulfate springs, which can also look gentle and therefore be easily confused, the difference becomes clearer.
| Spring type | Appearance | Smell | Tendency |
|---|---|---|---|
| Simple hot spring | Colorless and clear | Almost odorless | Less than 1,000 mg of dissolved substances, with no standout main component, gentle overall |
| Chloride spring | Colorless to lightly colored | Gentle to slightly salty | Chloride ions are the main component. It is often described as keeping the body warm after bathing |
| Sulfate spring | Often colorless and clear | Gentle | Sulfate ions are the main component. The type varies depending on the cation |
| Sulfur spring | May be cloudy white | Sulfur-like odor | Sulfur components are the main component. Strong and distinctive character |
As this table shows, if you want a strong character, sulfur springs or iron-rich springs are good choices, while if you want gentleness and ease of bathing, a simple hot spring is a better fit. This is not a matter of one being better than the other; they simply offer different experiences. For the overall positioning of all 10 therapeutic spring types, see the Onsen Spring Types Guide.
Also, simple hot springs, chloride springs, and sulfate springs are hard to distinguish just by looking at the water on site. The most reliable method is to check the spring analysis sheet displayed in the changing room or bath area.
Simple hot springs may also be listed with general bathing indications based on the Ministry of the Environment’s guidelines. These general indications are shared by therapeutic springs regardless of spring type and include things like stiffness in muscles and joints, as well as mild fatigue. However, this framework assumes repeated use over a period of time and does not guarantee any effect from a single bath.
Because simple hot springs are gentle, they are less likely to be promoted with strong effects tied to specific mineral content. For that reason, it is more practical to choose them for their mildness and ease of bathing rather than expecting special benefits. Individual differences are large, so it is unwise to take the listed indications too literally or to expect too much.
Simple hot springs are well suited to people who are not used to hot springs, people who dislike strong water, and people who want to bathe slowly and comfortably. They are easy to choose for those who value rest and convenience more than mineral character. They are also a good choice in situations such as family trips, where the ages and conditions of the bathers vary.
On the other hand, some people may find them underwhelming if they are looking for clear personality, such as cloudy water or a strong smell. In that case, comparing them with more distinctive spring types can actually make the calmness of simple hot springs easier to appreciate. When choosing a hot spring destination, it helps to look not only at the spring type but also at whether the water is free-flowing, whether it is diluted or reheated, and whether the temperature suits your preferences.
No, it does not mean the water is weak in minerals. Simple hot springs still contain various dissolved components, but because the amount of any specific component does not reach the required standard for a named spring type such as chloride spring or sulfate spring, they are classified as simple hot springs. Under the Ministry of the Environment’s criteria, they refer to water with less than 1,000 mg of dissolved substances per 1 kg, excluding gases, and a spring temperature of 25°C or higher. It is more accurate to think of them as balanced springs without a standout main component.
Alkaline simple hot springs are the subset of simple hot springs with a high pH, generally 8.5 or above. Alkaline water is said to soften the skin’s outer layer, and because of its smooth feel, it is sometimes introduced as a beauty bath. However, not all simple hot springs feel the same, and waters close to neutral may not produce much of that smooth sensation. The relationship between pH and skin feel is explained in detail in the Onsen pH Guide.
In alkaline simple hot springs, you may feel a smooth sensation after bathing, and some hot spring resorts are called beauty baths, but this is a traditional nickname based on texture and does not guarantee cosmetic benefits. Experiences vary from person to person, and this article does not claim any definite effect.
It is difficult. Simple hot springs are often colorless and clear, with a gentle smell, so they are hard to distinguish visually from chloride springs or sulfate springs. The most reliable way is to check the spring analysis sheet posted in the changing room or bathing area.
Yes, they are a good fit. Because they are relatively mild and often nearly colorless, tasteless, and odorless, they are considered easy for people who are not used to hot springs, people who want to avoid long soaking, and families. That said, some facilities still have high water temperatures, so it is reassuring to start with a short soak.
A simple hot spring is a therapeutic spring with less than 1,000 mg of dissolved substances per 1 kg, excluding gases, and a spring temperature of 25°C or higher. Despite the impression created by its name, it is not poor in minerals; it is simply a balanced spring without an outstanding main component, because no specific component has reached the required amount for a named spring type. Since it is often nearly colorless, tasteless, odorless, and gentle on the body, it is well suited to onsen beginners, people who want to avoid long soaking, and families.
When the pH is high, it is called an alkaline simple hot spring, and it may be introduced as a beauty bath because of its smooth skin feel. However, not all simple hot springs feel the same. If you want strong personality, other spring types may be better; if you want gentleness and ease of bathing, simple hot springs are a great choice. For the full picture of each spring type, see the Onsen Spring Types Guide, and for details on pH and skin feel, see the Onsen pH Guide.
A simple hot spring is one of the 10 types of therapeutic springs. It is a spring type in which the dissolved components in the hot spring water do not reach the standard amount required for a specific spring classification. Under the Ministry of the Environment’s criteria, it refers to water with less than 1,000 mg of dissolved substances (excluding gaseous ones) per 1 kg of hot spring water and a spring temperature of 25°C or higher. Because it has the word simple in its name, it is often misunderstood as weak in minerals, but this is only a classification label and does not mean the water is thin or low in value.
In short, simple hot springs are often nearly colorless, clear, tasteless, and odorless, with gentle stimulation that makes them easy to enter. For that reason, they are often suitable for onsen beginners, people who want to avoid long soaking, and families. On the other hand, they may feel understated to those seeking a strong character. This article explains the definition of simple hot springs, their features, their relationship with alkaline simple hot springs with high pH, and their position among other spring types, based on the Ministry of the Environment’s criteria. For the full picture of all 10 therapeutic spring types, see the Onsen Spring Types Guide; here, we focus only on simple hot springs.
This article provides general information and does not guarantee any specific therapeutic or beauty effects. If you have a chronic condition, are under treatment, or are not feeling well, do not push yourself and follow your doctor’s advice and the facility’s guidance.
Whether a spring is classified as a simple hot spring is determined by the amount of dissolved components in the water and the spring temperature. In the Ministry of the Environment’s Guidelines for Mineral Spring Analysis, simple hot springs are defined among therapeutic springs as water with less than 1,000 mg of dissolved substances per 1 kg of hot spring water, excluding gaseous substances, and a spring temperature of 25°C or higher. If a bathhouse displays labels such as simple hot spring or alkaline simple hot spring, the water meets this standard.
A common misunderstanding is that simple means weak in minerals. Simple hot springs do contain various dissolved components. However, sodium, sulfate ions, and other components have not reached the prescribed amount needed to be classified as a specific spring type such as chloride spring or sulfate spring. In other words, the name simple hot spring is just a classification, not a statement that the water is thin or less valuable. Put differently, it is a balanced spring without an outstanding main component, not water with little total mineral content.
| Item | Details |
|---|---|
| Dissolved substances, excluding gases | Less than 1,000 mg per 1 kg of hot spring water |
| Spring temperature | 25°C or higher |
| Appearance and smell | Often nearly colorless, tasteless, and odorless |
| Alkaline simple hot spring | The above plus pH 8.5 or higher |
If the dissolved substances are 1,000 mg or more, or if a specific component exceeds the prescribed amount, the spring is not classified as a simple hot spring and instead becomes a chloride spring, sulfate spring, or bicarbonate spring, among others. The definition of hot springs themselves, such as the minimum standards for temperature and components, is separate from the definition of simple hot springs, so reading What Is an Onsen? as well can make it easier to understand where a hot spring begins and where a therapeutic spring begins.
Simple hot springs tend not to have a strong visual or aromatic character. They lack obvious markers such as the cloudy white appearance of sulfur springs or the reddish-brown color of iron-rich springs, and they are often colorless, clear, and only gently scented. Some people may feel disappointed if they expect a strongly distinctive onsen, but many others appreciate this calmness for the sense of comfort it brings.
Because they are considered relatively mild, they are a good match for people who are not used to hot springs, people who want to avoid long soaking, or situations where they want to bathe comfortably while monitoring their condition. They are also easy to choose for family trips where people of different ages are bathing together. That said, even if the water feels gentle, facilities with high water temperatures can warm the body more than expected, so it is safer to start with a short soak rather than staying in too long.
Rather than focusing on mineral character, it is easier to understand simple hot springs as springs that let you enjoy the comfort of bathing itself and the slow, relaxing time spent in a hot spring resort.
Among simple hot springs, those with a high pH are called alkaline simple hot springs. In general, this refers to water with a pH of 8.5 or higher, and bath signs often distinguish them with the label alkaline simple hot spring.
Alkaline water is said to soften the outer layer of the skin, and during or after bathing you may feel that your skin becomes smooth and slippery. Because of this texture, some hot spring resorts are introduced as beauty baths, but this is only a traditional nickname based on how the skin feels, not a guarantee of cosmetic benefits. Experiences vary from person to person, and this article does not make definitive claims about effects. For more on the relationship between pH and skin feel, and how to tell alkaline springs from acidic ones, see the Onsen pH Guide.
One important point is that not all simple hot springs have the same feel. Even within the simple hot spring category, pH and mineral composition vary, and waters that are close to neutral do not create the same smooth sensation as alkaline simple hot springs. Even if two springs are both called simple hot springs, the impression can differ greatly from one source to another.
The position of a simple hot spring lies in the fact that it does not have one outstanding main component. When compared with chloride springs or sulfate springs, which can also look gentle and therefore be easily confused, the difference becomes clearer.
| Spring type | Appearance | Smell | Tendency |
|---|---|---|---|
| Simple hot spring | Colorless and clear | Almost odorless | Less than 1,000 mg of dissolved substances, with no standout main component, gentle overall |
| Chloride spring | Colorless to lightly colored | Gentle to slightly salty | Chloride ions are the main component. It is often described as keeping the body warm after bathing |
| Sulfate spring | Often colorless and clear | Gentle | Sulfate ions are the main component. The type varies depending on the cation |
| Sulfur spring | May be cloudy white | Sulfur-like odor | Sulfur components are the main component. Strong and distinctive character |
As this table shows, if you want a strong character, sulfur springs or iron-rich springs are good choices, while if you want gentleness and ease of bathing, a simple hot spring is a better fit. This is not a matter of one being better than the other; they simply offer different experiences. For the overall positioning of all 10 therapeutic spring types, see the Onsen Spring Types Guide.
Also, simple hot springs, chloride springs, and sulfate springs are hard to distinguish just by looking at the water on site. The most reliable method is to check the spring analysis sheet displayed in the changing room or bath area.
Simple hot springs may also be listed with general bathing indications based on the Ministry of the Environment’s guidelines. These general indications are shared by therapeutic springs regardless of spring type and include things like stiffness in muscles and joints, as well as mild fatigue. However, this framework assumes repeated use over a period of time and does not guarantee any effect from a single bath.
Because simple hot springs are gentle, they are less likely to be promoted with strong effects tied to specific mineral content. For that reason, it is more practical to choose them for their mildness and ease of bathing rather than expecting special benefits. Individual differences are large, so it is unwise to take the listed indications too literally or to expect too much.
Simple hot springs are well suited to people who are not used to hot springs, people who dislike strong water, and people who want to bathe slowly and comfortably. They are easy to choose for those who value rest and convenience more than mineral character. They are also a good choice in situations such as family trips, where the ages and conditions of the bathers vary.
On the other hand, some people may find them underwhelming if they are looking for clear personality, such as cloudy water or a strong smell. In that case, comparing them with more distinctive spring types can actually make the calmness of simple hot springs easier to appreciate. When choosing a hot spring destination, it helps to look not only at the spring type but also at whether the water is free-flowing, whether it is diluted or reheated, and whether the temperature suits your preferences.
No, it does not mean the water is weak in minerals. Simple hot springs still contain various dissolved components, but because the amount of any specific component does not reach the required standard for a named spring type such as chloride spring or sulfate spring, they are classified as simple hot springs. Under the Ministry of the Environment’s criteria, they refer to water with less than 1,000 mg of dissolved substances per 1 kg, excluding gases, and a spring temperature of 25°C or higher. It is more accurate to think of them as balanced springs without a standout main component.
Alkaline simple hot springs are the subset of simple hot springs with a high pH, generally 8.5 or above. Alkaline water is said to soften the skin’s outer layer, and because of its smooth feel, it is sometimes introduced as a beauty bath. However, not all simple hot springs feel the same, and waters close to neutral may not produce much of that smooth sensation. The relationship between pH and skin feel is explained in detail in the Onsen pH Guide.
In alkaline simple hot springs, you may feel a smooth sensation after bathing, and some hot spring resorts are called beauty baths, but this is a traditional nickname based on texture and does not guarantee cosmetic benefits. Experiences vary from person to person, and this article does not claim any definite effect.
It is difficult. Simple hot springs are often colorless and clear, with a gentle smell, so they are hard to distinguish visually from chloride springs or sulfate springs. The most reliable way is to check the spring analysis sheet posted in the changing room or bathing area.
Yes, they are a good fit. Because they are relatively mild and often nearly colorless, tasteless, and odorless, they are considered easy for people who are not used to hot springs, people who want to avoid long soaking, and families. That said, some facilities still have high water temperatures, so it is reassuring to start with a short soak.
A simple hot spring is a therapeutic spring with less than 1,000 mg of dissolved substances per 1 kg, excluding gases, and a spring temperature of 25°C or higher. Despite the impression created by its name, it is not poor in minerals; it is simply a balanced spring without an outstanding main component, because no specific component has reached the required amount for a named spring type. Since it is often nearly colorless, tasteless, odorless, and gentle on the body, it is well suited to onsen beginners, people who want to avoid long soaking, and families.
When the pH is high, it is called an alkaline simple hot spring, and it may be introduced as a beauty bath because of its smooth skin feel. However, not all simple hot springs feel the same. If you want strong personality, other spring types may be better; if you want gentleness and ease of bathing, simple hot springs are a great choice. For the full picture of each spring type, see the Onsen Spring Types Guide, and for details on pH and skin feel, see the Onsen pH Guide.