Any spring whose water is above the ambient air temperature Conventially, in the United States, the spring should be at least 15 degrees Fahrenheit over the mean annual temperature of the air in their localities
A natural spring producing warm water, usually at a temperature above that of the human body. a place where hot water comes up naturally from the ground. or thermal spring Spring that issues water at temperatures substantially higher than the air temperature of the surrounding region. Most hot springs result from the interaction of groundwater with magma or with solid but still-hot igneous rocks. Some, however, are not related to volcanic activity. In such cases, deep circulation of water is thought to carry the water to the lower parts of the Earth's crust, where the temperature of the rocks is high