Japan Mineral Spring Guide 2025

Arima is famous for having two completely different spring types at one location: kinsen (golden spring) — a dark reddish-brown iron-sodium spring so rich in minerals it stains towels orange — and ginsen (silver spring), a clear, mildly carbonated simple spring. Bathing in both types at one visit is a unique experience available nowhere else in Japan.

Misasa Onsen in Tottori Prefecture has the world's highest confirmed radon concentration in a natural hot spring. The town markets itself on the hormesis effect — the theory that low-level radiation stimulates cellular repair. The local population has historically lower rates of certain cancers, a correlation studied by Japanese and international researchers. The spring itself looks and smells like a normal clear simple spring.

Kusatsu Onsen (Gunma) — Acidic Spring

Kusatsu's main source (Yubatake) produces water with a pH of 2.0 — highly acidic, with the characteristic egg smell of sulfur. The acidity is so extreme that metals corrode rapidly and certain treatments are prohibited (pregnant women, people with heart conditions, open wounds). The traditional “yumomi” water-cooling ritual — stiring with large wooden paddles — was developed specifically because Kusatsu's water is too hot to cool by dilution without destroying its mineral content.