Non-volcanic hot springs are further divided into deep hot water, which was heated by geothermal heat that becomes higher according to the geothermal gradient, and those whose heat source is unknown.
非火山性温泉はさらに、地下深くほど温度が高くなる地温勾配に従って高温となったいわゆる深層熱水と、熱源不明のものに分けられる。