Hot spring water type refers to a classification of the minerals dissolved in the water. Labels such as “sulfur spring,” “bicarbonate spring,” and “chloride spring” seen at Japanese hot spring resorts express the character of the water in a single phrase.

In short, beginners do not need to memorize everything. First, grasp the broad differences among the 10 therapeutic spring types and the key points to check first in the mineral analysis sheet, and you will be able to understand what kind of water a hot spring has. This article organizes those essentials based on Ministry of the Environment standards.

“Hot spring” and “hot spring with a water type name” are not the same

First, let’s separate two confusing terms.

One is the legal definition of a hot spring. Under the Hot Springs Act, water is defined as a “hot spring” if the source temperature is 25°C or higher, or if it contains at least one of the 19 specified components at or above the regulated amount, even if the temperature is lower.

The other is a therapeutic spring. This is a hot spring that meets the stricter standards set by the Ministry of the Environment’s “Guidelines for Mineral Spring Analysis,” and only therapeutic springs are given one of the 10 water type names. If you see a sign that says “○○ spring,” you can think of it as meeting the conditions for a therapeutic spring. The requirements are that the total dissolved solids are 1,000mg/kg or more, or that specific components are present at or above the regulated levels.

Quick reference table of the 10 therapeutic spring types

Therapeutic springs are classified into the following 10 types according to the components they contain. Start with this table to get the full picture, then move on to the detailed explanation of any type that catches your interest.

The figures are based on the Ministry of the Environment’s Guidelines for Mineral Spring Analysis (revised in 2014). The representative hot spring areas are only examples, and even within the same area, the water type differs by source.

Five places to check first on the analysis sheet

You do not need to read every detail of the “hot spring analysis report” posted in the changing room or bath area. Beginners can get a rough sense of the water by checking these five points.

• Water type name — Which item from the table above it matches. The starting point for the spring’s character.
• Source temperature — Whether it is lukewarm or high-temperature water. See the temperature classification for the rough range.
• pH (acidity/alkalinity) — Acidic or alkaline. This directly affects how it feels on the skin (next section).
• Osmotic pressure — Whether it is hypotonic, isotonic, or hypertonic. See how to read osmotic pressure.
• Usage status — Whether it is diluted with water, heated, circulated, or free-flowing. Explained in the difference between gensen kakenagashi and circulation.

For a more detailed explanation, see how to read a hot spring analysis report.

How pH changes the feel on your skin

Along with the water type name, pH (acidity/alkalinity) is another major factor that affects the bathing experience. The Guidelines for Mineral Spring Analysis classify it roughly as follows.

Acidic water tends to feel more irritating on the skin and is considered to have antibacterial properties, while alkaline water is said to soften dead skin cells and sebum, so it is often described as “slippery” or “silky.” However, this is only a description of the feel and does not guarantee any cosmetic effect. For details, see how to read pH values.

Do not choose a hot spring by water type name alone

It is best to avoid oversimplifications such as “sulfur spring is the best” or “simple spring is boring.” The actual bathing experience is determined not only by the water type name, but also by the temperature, whether water is added or heated, whether it is circulated, and even the size and crowding of the bath area.

For example, even a simple spring with a low mineral content can feel much more pleasant than a stronger spring if it is free-flowing from the source and at a comfortable temperature. A water type is a clue for understanding the water; it is not a ranking of better or worse.

How beginners should choose

If you are unsure, choose in this order:

1. First choose a facility with a water temperature that feels comfortable.
2. Try a water type that caught your attention in the table, such as sulfur spring, which often has a distinct smell and color, bicarbonate spring, which is known for its skin feel, or chloride spring, which is said to help you stay warm.
3. Start with a short soak if the water is strongly acidic or has a strong sulfur smell.

Rather than aiming for a famous water type, it is more satisfying to find water that feels good to you.

Basic bathing tips and precautions

Even if the water type changes, the basic way to bathe stays the same. Rinse your body before entering, do not stay in too long at first, get out before you feel overheated, and hydrate before and after.

However, for strongly stimulating waters such as acidic springs or highly mineralized waters such as sulfur springs, it is best to start with a shorter soak. Older adults and people with chronic conditions should also check the precautions before entering a hot spring.

Frequently asked questions

Do I need to memorize all the water type names?

No. It is enough to know the 10 names and the general tendencies of smell, color, and skin feel. You can check the rest on the analysis sheet on the spot.

Do “beauty spring” and “skin-beautifying spring” really help the skin?

These are not legal water type names, but customary labels. Alkaline or bicarbonate springs may feel smoother on the skin, but they do not guarantee cosmetic effects.

If the water type is good, does that mean the hot spring is good?

Water type is only one factor. The bathing experience changes greatly depending on the water temperature, usage conditions such as dilution, heating, and circulation, and the facility environment.

Can I feel the effects of a water type in one bath?

Warmth and skin feel can often be noticed right away, but the indicated benefits of therapeutic springs are generally based on repeated use over time. Individual differences are large, so do not expect too much.

Summary

A water type is a classification that shows the character of the minerals dissolved in a hot spring, and only hot springs that meet the standards are given a water type name as a therapeutic spring. If you understand the broad differences among the 10 types and the five points to check on the analysis sheet—water type name, source temperature, pH, osmotic pressure, and usage status—you can read the character of a hot spring even on your first visit. Do not overthink it; start with the one bath that feels good to you.

Sources

• Ministry of the Environment: “Protection and Use of Hot Springs — Definition of a Hot Spring”
• Ministry of the Environment: “Guidelines for Mineral Spring Analysis (Revised in 2014)”
• Japan Spa Association: “Different Types of Hot Spring Water”