Tamagawa Hot Spring — photo: Own work · CC BY-SA 3.0 · Wikimedia Commons
The 3 most unusual onsen waters in Japan
Most onsen water in Japan is one of a few common kinds: salty, smooth, or mild and clear. If you want water that is genuinely different, go to Toyotomi in northern Hokkaido for iodine water with an oily film, Tamagawa in Akita for water at 98 °C and pH 1.05, or Kusatsu in Gunma for acid water in a full-size town. Each is the best-known town for one of the three rarest water types in our records. We did not pick them because the water is "better" or does you more good — we make no such claims — but because it is the least like what you will find anywhere else.
Why these three, in one paragraph
Japanese law sorts hot spring water into ten types, and the sign in every changing room says which ones a source has (our water types guide explains how to read it). We hold at least one type for 1,468 onsen towns. Seven of the ten types turn up in more than 80 towns each. Three do not: iodine in 13 towns, carbon dioxide in 21, and acidic in 47. For each of those three we took the town whose Wikipedia article is read most often, as a measure of how established it is — whether it has inns, a way to get there, and a bath that takes visitors. That gives Toyotomi for iodine, Tamagawa for carbon dioxide, and Kusatsu for acidic. The full method is at the end.
1. Toyotomi: the oily water at the top of Japan
Why it made it. Toyotomi Onsen is the best-known of the 13 iodine towns, at 965 in our count, ahead of Izu Nagaoka at 832.
The water. Our records list it as iodine with chloride and bicarbonate, at 34.2 °C at source. What people remember is not the iodine but what comes up with it: the water carries a film of oil and smells of petroleum, because the source was found while drilling for oil. Nothing else on this page looks or smells like it. At 34.2 °C it is cooler than a bath, so expect it to be warmed; the notice in the changing room will say so.
The town. It is small: our records list 9 inns, around a public bathhouse. Toyotomi is on the edge of the Sarobetsu wetlands, and Panke-numa, a marsh lake, is 10.4 km away. Wakkanai, the northern tip of Japan, is the nearest city.
Getting there. Take the JR Sōya Line north from Sapporo to 豊富 (Toyotomi), then a local bus of about 10 minutes for the last 6.3 km. Our estimate from Sapporo is about five hours. The JR Pass covers the train. Trains on the Sōya Line are few, so plan the day around them.
Good for: anyone who wants a water they will never confuse with another, and anyone already going to Wakkanai or Rishiri. Watch out for: the smell stays on skin and hair, and it is a long way from anywhere. Our Hokkaido guide has the distances.
2. Tamagawa: the hottest, sharpest water in one inn
Why it made it. Tamagawa Hot Spring is the best-known of the 21 carbon dioxide towns, at 2,366 in our count. It is also the only town in our records listed as both carbon dioxide and acidic.
The water. One source, recorded at 98 °C and pH 1.05, with a flow of about 9,000 litres a minute. Only 30 of the 1,167 towns with a recorded temperature reach 95 °C, and only 11 of the 596 with a recorded pH go below 2; Tamagawa is in both groups. Its full name on the sign lists acid, carbon dioxide, iron and aluminium with chloride. Do not expect bubbles: the carbon dioxide is there by the chemical definition, but what you notice is the acid. It stings any small cut, and the inn also offers diluted baths.
The place. Tamagawa is not a town but a single large inn in the mountains north of Lake Tazawa, with steaming ground around it. Akita-Yakeyama, the volcano behind it, is 2.3 km away; Yasu Falls is 10 km.
Getting there. Take the Akita Shinkansen to 田沢湖 (Tazawako), then a bus of about 1 hour 20 minutes. Our estimate from Tokyo is about five hours. The JR Pass covers the train, not the bus.
Good for: the strongest water you can bathe in, and anyone combining it with Nyuto on the same trip. Watch out for: it closes for the winter, roughly from December to April. Check the bus times before you go, and keep the water away from your eyes. Our Tohoku guide covers the area.
3. Kusatsu: acid water in a real town
Why it made it. Kusatsu Onsen is the best-known of the 47 acidic towns by a wide margin, at 5,664. Tamagawa, at 2,366, is second.
The water. Acidic, sulfur, sulfate and chloride, at pH 1.0 to 2.2 and 44.9 to 94.5 °C between its sources. Its pH is as low as Tamagawa's, and the only town in our records with a lower one is Kawayu in Hokkaido, at 0.8. What makes Kusatsu different from the other two is volume: about 32,300 litres a minute for the town, which puts it among only 12 of the 425 towns with a recorded flow that produce 10,000 or more. That is enough water for 171 inns.
The town. The centre is the 湯畑 (yubatake), an open channel of steaming water that cools it before it reaches the baths, with public bathhouses and footbaths around it. Kōsen-ji temple is about 200 m away. In winter the Kusatsu Onsen ski area is 1.2 km away. Our Kusatsu guide covers the town in detail.
Getting there. Take the JR limited express from Ueno to 長野原草津口 (Naganohara-Kusatsuguchi), then a bus of roughly 25 minutes. There are also direct highway buses from Tokyo. Our estimate is about three hours, and you do not need a car.
Good for: a first taste of strong water with all the comforts of a large town, and the easiest of the three to reach. Watch out for: the acid tarnishes silver and stings cuts, and the sulfur smell carries; see sulfur onsen.
Which of the three?
- Only one night, from Tokyo: Kusatsu.
- The strongest water, and you do not mind a remote single inn: Tamagawa, outside winter.
- A water nobody else has, and you are going to northern Hokkaido anyway: Toyotomi.
- Acid water, two ways: Kusatsu and Tamagawa are both pH 1-ish. Do one, not both, unless that is the whole point of your trip.
The towns that only just missed
If you want carbon dioxide you can actually feel, go to Nagayu Onsen in Ōita, second in that group at 1,184. It is recorded at 40 to 45 °C, one of the few carbon dioxide springs warm enough to sit in for long, and the bubbles cling to your skin. It is about 50 minutes by bus from Bungo-Taketa Station, and Oka Castle is 11.3 km away. Nanki-Shirahama in Wakayama was third, at 1,094.
For iodine, Izu Nagaoka in Shizuoka was second at 832. It is much easier to reach than Toyotomi — about an hour and three quarters from Tokyo in our estimate, the last line being the Izuhakone Railway, which the JR Pass does not cover — and has 36 inns. The water is recorded as alkaline simple water at pH 9.2 and 59 °C, clear rather than oily.
For acid, Beppu (2,195) and Manza (1,969) came next after Tamagawa. Manza is on the same volcano as Kusatsu, higher up, and like Tamagawa it is cut off in winter.
The fourth-rarest type, iron, is found in 81 towns, and the rest are commoner still, so we stopped at three.
How we picked these three
- Starting pool: 1,468 onsen towns with at least one recorded water type.
- Rarest types: iodine (13 towns), carbon dioxide (21) and acidic (47). Every other type is found in at least 81 towns.
- Known: within each type, ranked by how often each town's Wikipedia article is read. Iodine: Toyotomi 965, then Izu Nagaoka 832. Carbon dioxide: Tamagawa 2,366, then Nagayu 1,184. Acidic: Kusatsu 5,664, then Tamagawa 2,366.
- Not used: health effects, scenery, inn quality, price, tattoo policy or distance from a city. We make no claims about what any water does for you, and we have no data that ranks the rest fairly.
- About the records: a type name is a chemical threshold, and a town is listed under every type it has. That is why Tamagawa counts as carbon dioxide water without being fizzy. Temperatures, pH and flow are as recorded in the sources we hold, and a town's baths may be cooled, warmed or diluted.
- Travel times are rough estimates from station locations, not a timetable. Check the route on Google Maps before you go.
To browse every town with one water type, start from the type pages: iodine, carbon dioxide and acidic. For what the sign in the changing room means, read onsen water types; for the milky water most people picture, sulfur onsen. Want the easiest first trip rather than the strangest water? See the 3 best onsen towns in Japan for a first trip. New to this? Start with how an onsen stay actually works and onsen etiquette.