HOT SPRING

There is no universally accepted definition of a hot spring. For example, one can find the phrase hot spring defined as
* any geothermal spring[1]
* a spring with water temperatures above its surroundings[2]
* a natural spring with water temperature above body temperature – normally between 36.5 and 37.5 °C (98 and 100 °F)[3]
* a natural spring with warm water above body temperature[4]

Guelma in Algeria
* a thermal spring with water warmer than 36.7 °C (98 °F)[5][6]
* a natural spring of water greater than 21.1 °C (70 °F) (synonymous with thermal spring)[7][8][9][10]
* a natural discharge of groundwater with elevated temperatures[11]
* a type of thermal spring in which hot water is brought to the surface. The water temperature of a hot spring is usually 6.5 °C (12 °F) or more above mean air temperature.[12] Note that by this definition, "thermal spring" is not synonymous with the term "hot spring"
* a spring whose hot water is brought to the surface (synonymous with a thermal spring). The water temperature of the spring is usually 8.3 °C (15 °F) or more above the mean air temperature.[13]
* a spring with water above the core human body temperature – 36.7 °C (98 °F).[14]
* a spring with water above average ambient ground temperature,[15] a definition favored by some
* a spring with water temperatures above 50 °C (122 °F)[16]

Hot spring in Lassen Volcanic National Park

The related term "warm spring" is defined as a spring with water temperature less than a hot spring by many sources, although Pentecost et al. (2003) suggest that the phrase "warm spring" is not useful and should be avoided.[14] The US NOAA Geophysical Data Center defines a "warm spring" as a spring with water between 20 and 50 °C (68 and 122 °F).
SOURCE:
http://en.wikipedia.org/wiki/Hot_spring