Sentō is a public bathhouse, mainly located in urban areas, where underground water or tap water is heated and used. Traditionally, it has been a place for people without a bath at home to come and bathe, but nowadays, many people visit sentō for relaxation purposes. It generally does not contain the natural minerals found in hot springs (onsen).
Onsen is a bathhouse that uses naturally heated water or steam that rises from underground. Only baths that meet the specific criteria set by the “Onsen Law” (such as water temperature and mineral content) are officially called “onsen.” Onsen water contains minerals and elements that are said to be beneficial for health, and many people visit for relaxation and therapeutic purposes.
In short, the main difference is that sentō are public bathhouses, while onsen use natural hot spring water. Each offers a unique way to relax and enjoy bathing.
Legal Perspective on Sentō and Onsen
From a legal standpoint, sentō and onsen are regulated by different sets of laws.
Sentō are operated under the Public Bathhouse Law, and they are typically located in urban or residential areas. The water used is usually heated tap water or groundwater, without the specific mineral content found in onsen. Another characteristic of sentō is that their fees are regulated by law, making them accessible and affordable for everyone.
Onsen, on the other hand, are operated under the Onsen Law, which mandates that the bathhouse uses naturally sourced hot spring water. The water must meet specific requirements regarding temperature (above 25°C) and the presence of certain minerals in order to qualify as an onsen. The Onsen Law also includes strict regulations regarding the composition of the water, and failure to comply with these standards can result in penalties.
Thus, from a legal perspective, sentō serve as a community-oriented public service, while onsen are treated as special facilities with expected health and therapeutic benefits.
Did You Know There Are Hot Springs in Tokyo?!
Living in Tokyo, you might only think of sentō (public bathhouses), but there are actually onsen (hot springs) here too!
- Kuroyu Onsen (Kamata)
In the Kamata area, you can enjoy a hot spring called “Kuroyu”, which means “black water” due to its dark color, sourced from underground. The water is rich in humic acid, which contains marine minerals that are great for the skin, and it doesn’t have an unpleasant smell.
The kuroyu water, heated with firewood, is one of the hottest baths in Tokyo. It has been featured on TV and in magazines multiple times for its intense heat. At Kamata Onsen, the water is undiluted—straight from the source with no added water.
- Toshimaen Niwa no Yu (Nerima)
At Niwa no Yu, you’ll find a natural hot spring, a variety of spa facilities, saunas, and more. The outdoor baths overlook a Japanese garden, offering views of seasonal plants and flowers, creating a tranquil environment surrounded by nature.
Here, you can experience bade, a traditional German bath method, while the facility also offers relaxation areas and a dining space where you can enjoy seasonal dishes.
- Onsen Sentō (Machida, Itabashi, etc.)
Even though these baths have natural hot spring water, they are still classified as sentō (public bathhouses) because they are general public facilities. Tokyo has many onsen sentō, including in areas like Machida and Itabashi, where you can enjoy natural hot springs.
That concludes our discussion on the difference between sentō and onsen for today. Thank you for reading! 😊