「鉱泉分析法指針」（平成26年改訂）

【1】Classification by "Spring quality" of Therapeutic springs

The "Guideline to the Mineral Spring Analysis Methods" were revised in July 2014, and the names of the spring qualities were classified into 10 categories.
The 10 spring qualities are divided into 3 groups, as shown in the table below.

Group	Characteristics	Spring Quality for Notification
Simple hot springs	Hot springs with a temperature of 25℃ or higher and less than 1000 mg/kg of dissolved substances (excluding gas substances) in 1 kg of hot spring water.	①Simple hot springs
Saline springs	Hot springs with dissolved substances (excluding gas substances) of 1000 mg/kg or more in 1 kg of hot spring water, classified by the main component of anions.	②Chloride springs ③Hydrogen carbonate springs ④Sulfate springs
Hot springs containing special components	Hot springs with dissolved substances (excluding gas substances) not less than 1000 mg/kg but containing a certain amount of special components.	⑤Carbon dioxide springs ⑥Iron containing springs ⑦Acidic springs ⑧Iodine containing springs ⑨Sulfur springs ⑩Radioactive springs

For the characteristics of each spring quality, please refer to the previous section"STEP② 10 springs and Indications/Contraindications".

【2】Classification by "Osmotic pressure"

In the Hot Spring Analysis Report, where the name of the spring quality is written, for example, "Hypotonic, Neutral, High temperature hot spring" etc., the "osmotic pressure classification", "liquidity classification", and "spring temperature classification" are listed alongside the name of the spring.
One of them, "osmotic pressure" is the pressure that occurs between aqueous solutions of different concentrations; in other words, the pressure that causes water to move from the less dense side to the more dense side in an attempt to maintain a constant concentration.
Of these, "isotonic" means having the same "osmotic pressure" as human body fluid, and the liquid is called "isotonic liquid".
"Isotonic liquid" is equivalent to a saline solution of 9 g of salt dissolved in 1 liter of water.
Based on this as a standard, it is classified into 3 categories as shown in the table below.

Hypotonic	Lower osmolality than isotonic liquid	Less than 8g/kg	Water enters the body (easy to absorb water/easy to become wrinkled or softened)
Isotonic	Same osmolality as isotonic liquid	8g/kg or more Less than 10g/kg
Hypertonic	Higher osmolality than isotonic liquid	10g/kg or more	Water leaves the body (easy to absorb components/easy to get hot spring fatigue)

Sports drinks can be classified into two categories: isotonic and hypotonic. Isotonic drinks have the same osmotic pressure as human body fluid. In other words, sports drinks that are “isotonic” allow the body to absorb water, carbohydrates, and salt. It is recommended to drink before exercise (when the concentration is the same). Hypotonic drinks have a lower concentration of salt and carbohydrates and a lower osmotic pressure than that of human body fluids. Therefore, it is absorbed by the body faster than an “isotonic” sports drink (isotonic beverage). It is similar in concentration to the oral rehydration solution that is drunk when dehydrated, and is considered good for rehydration during and immediately after exercise.
As with these sports drinks, the “osmotic pressure” value is important as a guide when entering a hot spring. As an effect on the body, water is easily absorbed by the body when bathing in a “hypotonic” hot spring. This may result in wrinkling of the fingertips, which is a characteristic of hypotonic hot springs.
On the other hand, when you bathe in a “hypertonic” hot spring, the water in your body is more likely to leave your body. A long soak in a hot spring can easily cause dehydration. At the same time, the components of the hot spring are more easily absorbed by the body, which can lead to hot spring fatigue. Generally, a “hypertonic” hot spring can be said to be a rich spring.

【3】Classification by "Hydrogen ion concentration (pH)/Liquidity"

The "pH value" is listed in the "Examination and test results at gushing location" column of the Hot Spring Analysis Reports.
Chemically, pH 7.0 is considered neutral, lower pH is acidic, and higher pH is alkaline.
The "Guideline to the Mineral Spring Analysis Methods" classify the liquid properties of mineral springs according to the pH value at the time of gush as shown in the table below.

Strong Acid	Less than pH 2	※Current "Guideline to the Mineral Spring Analysis Methods" state that any pH less than 2 is also acidic
Acid	pH 2 or more to less than pH 3	↑↑Antibacterial effect (prickling and tingling)
Weak acid	pH 3 or more to less than pH 6	↑Antibacterial effect (tingling)
Neutral	pH 6 or more to less than pH 7.5
Weak Alkali	pH 7.5 or higher to less than pH 8.5	↓Skin beautifying effect (silky)
Alkali	pH8.5 or more	↓↓Skin beautifying effect (mushy and silky)
Strong Alkali	pH10 or more	※Current "Guideline to the Mineral Spring Analysis Methods" state that any pH more than 8.5 is also alkaline

【4】Classification by "Spring temperature"

The temperature of a mineral spring when it gushes to the ground or when it is collected is called the "spring temperature". The "spring temperature" is listed in the "Examination and test results at gushing location" column of the Hot Spring Analysis Report.
If the temperature at the time of collection from the source is 25℃ or more, it is considered a "hot spring" regardless of the amount of dissolved substances.
The classification is as follows according to the temperature of the spring.

	Classification	Spring temperature	If the temperature of the spring is reflected in the name of the spring, it will be described as follows. (Example) If the temperature is less than 25℃ → "Sodium-Chloride cold mineral spring". If the temperature is more than 25℃ → "Sodium-Chloride spring".
Mineral spring	Cold mineral spring	Less than 25℃
Hot spring	Low temperature spring	25℃ or more to less than 34℃
	Hot spring	34℃ or more to less than 42℃
	High temperature spring	42℃ or more

The suitable temperature for bathing in hot springs is considered to be 40-42℃, but natural hot springs do not have such a convenient spring temperature for humans.
That is why we use various methods to control the temperature.
While hot spring facilities equipped with a circulation and filtration system do not require much time and effort because the computer controls the temperature, facilities that use only the spring water from the source require a great deal of time and effort. For example, facilities with spring temperatures close to 100℃ add cold groundwater to the hot spring water, and facilities that insist on using 100% spring water use so-called heat exchange methods, for example, running a long pipe from the source well to the bathtub and submerging that pipe in the adjacent river bed to lower the temperature.
On the other hand, low-temperature hot spring facilities must be heated, but heating does not damage the components of the hot spring as much as adding water does. In addition, Carbon dioxide springs and Radioactive springs are prone to deterioration of the hot spring itself, making it necessary to use the 100% free-flowing method. In particular, Carbon dioxide springs are often bathed at the temperature of the gushing spring because the bubbles that cling to the skin disappear when the spring temperature exceeds 35 to 37℃. Although it is inevitably a long bath, even at 35-37℃, the active components of carbon dioxide gas will promote blood circulation, and in many cases, you will feel a warming sensation after the bath.