The response of researchers to a questionnaire on the definitions of hot, thermal, warm, and cold springs is provided. Two important benchmarks are recognized, the human body temperature and the mean annual local air temperature. While no scheme can claim to provide an objective, unbiased classification, waters emerging with a temperature in excess of the core human body temperature of 36.7 °C should be defined as hot springs. The term "thermal spring" is not recommended as it cannot be defined satisfactorily for all springs. The term "warm spring" is not considered utilitarian.