Kasamatsu Kosen

Kasamatsu Kosen is a cold spring — kosen indicating a natural emergence temperature below the 25°C threshold required for hot spring classification under Japanese law — distinguished by an exceptionally rare triple mineral composition combining bicarbonate alkalinity, magnesium content, and naturally dissolved carbon dioxide, making it one of the more mineralogically unusual and scientifically interesting cold mineral springs in Japan's extensive natural water heritage. The presence of magnesium in this spring's mineral profile — a mineral less commonly featured in Japanese onsen classifications than the more standard calcium, sodium, and sulfate compounds — reflects the specific geological formations through which the water travels, where magnesium-bearing rock strata contribute a distinctive mineral character within a long thermal tradition. Kasamatsu Kosen invites visitors to discover the scientific and sensory diversity of Japan's natural mineral water heritage beyond the volcanic hot springs that typically define onsen culture, where a cold magnesium-bicarbonate-carbonated spring represents the intersection of rare geological chemistry and the ancient Japanese tradition of seeking renewal in naturally occurring mineral waters of all temperatures.