Water types

単純泉 · アルカリ性単純温泉

Colourless, effectively odourless and tasteless. Alkaline examples feel slippery, almost soapy, between the fingers.

食塩泉 · 強食塩泉 · 弱食塩泉

Colourless to pale yellow-brown. Unmistakably salty to taste. Leaves a faint salt tightness on the skin as you dry.

重曹泉 · 重炭酸土類泉 · 含重曹食塩泉

Usually clear. The give-away is the feel: genuinely slippery, the water seeming to glide rather than wet. Slightly salty-bitter if you taste it.

芒硝泉 · 石膏泉 · 正苦味泉

Clear, faintly bitter. Calcium examples often leave a chalky white crust around the spout — a good visual tell.

単純炭酸泉 · 含炭酸泉

Fine bubbles cling to every submerged inch of you within a minute — the most immediately recognisable water of the ten. Prickles pleasantly, and feels warmer than the thermometer says.

鉄泉 · 含鉄(II)泉 · 緑礬泉 · 赤湯

Cloudy rust-red to brown. Tastes and smells distinctly of iron, like blood or old pipework. Leaves red deposits on the bath rim.

酸性明礬泉 · 含硫黄酸性泉

Clear to faintly milky. Sour on the tongue, sharply so. You will discover every small cut you have.

よう素泉

Pale yellow to amber, with a medicinal smell much like antiseptic — not unpleasant, but startling if unexpected.

単純硫黄泉 · 硫化水素泉 · 含硫黄泉

Usually milky white or a bluish white, often with 湯の花 — flakes of mineral precipitate — drifting in it. The smell arrives before you reach the building.

放射能泉 · ラドン泉 · ラジウム泉 · 単純放射能泉

Colourless, odourless, and indistinguishable by feel from plain hot water. This is the one class you cannot detect with your senses at all — only the 温泉分析書 on the wall will tell you.