Based on Osmotic pressure, the Standard Methods of Analysis for Mineral Springs categorizes hot springs into those of low tonicity, isotonicity, and high tonicity in accordance with the mass of dissolved ingredients contained in 1 kg of hot spring water or their freezing points.
鉱泉分析法指針では浸透圧に基づき、温泉1キログラム中の溶存物質総量ないし氷点によって低張性・等張性・高張性という分類も行っている。