1. Medical treatment of a disease with baths or medicinal springs.
2. Immersion of part or all of the body in a mineral water bath as a form of therapy.
3. The treatment of diseases, injuries, and other physical ailments with baths and bathing; especially, in natural mineral waters.

Balneotherapy involves the treatment of diseases by bathing. It may involve hot or cold water, massage via moving water, relaxation or stimulation. Many mineral waters at spas are rich in particular minerals (silica, sulfur, selenium, radium) which can be absorbed via the skin.

The term balneotherapy has gradually come to be applied to everything relating to health-spa treatment, including the drinking of waters and the use of hot baths and natural vapor baths, as well as of the various kinds of mud and sand used for hot applications.