"Hot springs," sento, and super sento may look similar, but they are governed by different laws. Once you sort out the differences, it becomes clear why sento water is not always hot spring water, and why sento are cheap and uniform while super sento charge different prices by facility.

To begin with the conclusion, hot springs are defined by the Hot Springs Act, sento by the Public Bathing Act, and fees by the Price Control Order. Whether something is a hot spring and whether something is a sento are separate questions. This article explains the difference using primary sources.

Understanding the 3 categories through law

What is a hot spring? (Hot Springs Act)

Under the Hot Springs Act, a "hot spring" means hot water that springs from the ground and meets either of these conditions: a source temperature of 25°C or higher, or a prescribed amount of specific minerals. The Ministry of the Environment oversees this system. Hot spring inns and day-use hot spring facilities are places that use this water. For more on spring quality and components, see Hot Spring Types for Beginners. For how source water is used, see What Is Gensen Kakenagashi?.

What is a sento? (General public baths under the Public Bathing Act)

A "sento" falls under the category of general public baths in the Public Bathing Act. It is positioned as a bathing facility needed for public health and sanitation in everyday life, and is overseen by the Ministry of Health, Labour and Welfare. Its core facilities are bathtubs, washing areas, and changing rooms, making it a place for quick, everyday bathing.

The water in sento is often heated tap water, not necessarily hot spring water under the Hot Springs Act. However, some sento do draw from a hot spring source and use hot spring water. In other words, being a sento and being a hot spring can overlap. For the history of Japanese bathing culture, see History of Japanese Bathing Culture.

Why are sento cheap and uniform? (Price Control Order)

Bathing fees for sento (general public baths) are capped by each prefecture under the Price Control Order. Because sento must set prices within that limit, fees are cheap and uniform within each region. For example, Tokyo's cap is 550 yen for adults age 12 and older, as of 2025, unchanged from the previous year. Since the cap differs by prefecture and is reviewed annually, check the latest announcements from each local government for the current amount.

This pricing control exists because sento are treated as part of the local living infrastructure.

What is a super sento? (Other public baths)

Super sento, health resorts, and sauna facilities fall under other public baths in the Public Bathing Act. They are designed for leisure and multi-hour stays, with open-air baths, saunas, cold plunge baths, stone saunas, dining areas, and rest spaces.

Only general public baths (sento) are subject to fee control, so super sento can set their own prices freely. That is why fees differ from one facility to another. Note that "super sento" is a common term, not a legal term; in legal classification, it falls under "other public baths."

Frequently asked questions

Is sento water hot spring water?

Most sento use heated tap water, so it is not necessarily hot spring water. However, some "hot spring sento" do use spring water. Whether it is a hot spring and whether it is a sento are separate questions.

Why are sento cheap?

Because the fees for general public baths (sento) are capped by each prefecture under the Price Control Order. They are regarded as part of local living infrastructure.

What is the difference between a super sento and a sento?

Sento are facilities for everyday bathing with regulated, uniform fees, while super sento are leisure-oriented, offer more amenities, and have freely set prices. Legally, super sento are classified as "other public baths."

Are hot spring inns the same as sento?

No. Hot spring inns and day-use hot spring facilities use hot spring water under the Hot Springs Act, so their legal position differs from sento (general public baths), which are intended for everyday bathing.

Summary

Hot springs, sento, and super sento are governed by different systems: the Hot Springs Act, the Public Bathing Act, and the Price Control Order. Hot springs are facilities that use hot spring water under the Hot Springs Act. Sento are general public baths for everyday bathing, with regulated low fees. Super sento are leisure-oriented "other public baths" with free pricing. Sento water is not always hot spring water. Understanding these 3 separate axes makes it easier to choose the right facility.

Sources

• Ministry of the Environment: Definition of a Hot Spring
• Ministry of Health, Labour and Welfare: Overview of the Public Bathing Act
• Tokyo Metropolitan Government: Regulated Bathing Fee Rates for Public Baths (2025)