Hydrotherapywater therapyis the use of water to promote healing. It is one of the oldest, simplest, and most effective of all the natural therapies. Water treatments include taking natural spring waters internally for their beneficial mineral content, and external treatments such as bathing, douches, and taking exercise in water.

Water cures originated in the use of natural spring water, often minerally rich, and sometimes also naturally warm to hot or very cold, and spas or watering places where people went to 'take the cure' became popular all over Europe from the early 19th century. Many European spas were established during the time of the Roman occupation and are still in use. However, ordinary water is also used in hydrotherapy today. Water of either extreme of temperature is used, or can be used alternately. Hot water first stimulates and then relaxes, while cold water invigorates. Alternating hot and cold water stimulates blood and lymph circulation, relieves congestion, and tones tissues.

Through a variety of techniques, naturopaths use the therapy to improve circulation, stimulate the vital force, ease pain, reduce fever, relax the nervous system, and empty the bowels. Water therapy also contributes to encouraging the efficient elimination of wastes through the skin.