So you’ve heard of onsen, right? And have you heard of sentō? Onsen are one of the things Japan is famous for, besides of course karaoke, Hello Kitty and Mt. Fuji. You might also have heard that onsen are natural hot springs, heated by the restless earth under Japan (and yep, the same restlessness causes earthquakes too). A lot is written about onsen in travel guides, but very few of the guides mention sentō, onsen’s little sister. So, what’s the difference between onsen and sentō?
Both sentō and onsen are public baths. A sentō is always a public bath house, while an onsen can be an outdoor hot spring. Ah, did I say hot spring again? Yeah, that’s right, there is the big difference between the two. An onsen is a natural hot spring. A sentō runs on heated tap water.
In pre-war Japan very few houses had built-in baths. From as early as the beginning of the Edo period entire neighborhoods shared baths in public bath houses. In modern-day Japan on the other hand most if not all houses have their own baths or showers. The small neighborhood sento, which saw its heyday in the 1960′s, has become an endangered species.
Sentō’s much cooler sister, the onsen, has however seen its popularity increase steadily. Both sentō and onsen are places where people go to soak their tired bodies in hot water, the minerals that are inherently present in onsen water have made the onsen feel it’s too cool to hang out with its sister. Many onsen have been turned into day spa’s, with restaurants and more.
Fortunately though, the small neighborhood sentō is still around. At last count there were about 6,000 left in the whole of Japan, and a visit to a sentō gives a rare insight into Japanese culture.
The difference between onsen and sentō
With all that said, distinguishing between onsen and sentō sounds fairly straight forward, right? But the two are a little more intertwined than you might have thought. Some small neighborhood bath houses run on hot water that springs from the earth, thus being worthy of the term onsen. On the other hand some resort-style day spa’s run on plain old tap water (these are called super sentō).
With the success of the resort-style onsen, the smaller baths that happen to get their water from an onsen do usually make a point of telling the visitor about it. This usually happens in the form of wall-mounted boards that list all the health benefits that come from bathing in their water.
And then there are the small neighborhood bath houses that only have the word onsen in their name, but heat their tap water in the back room. And that’s perfectly okay, since they don’t actually advertise anything about their water. In these cases onsen is simply part of the name.