Hydrotherapy is widely used for the treatment and rehabilitation of patients, but it can also be applied to prevent diseases in healthy people. This review investigates the health effects of water immersion, a form of hydrotherapy, and the mechanisms by which the properties of water elicit such an effect. We searched PubMed, EMBASE, Cochrane Library, and CINAHL to identify relevant articles, of which 13 met the inclusion criteria. Various factors of water immersion were investigated in the 13 selected articles, including water temperature, immersion height, and application area. With respect to health effects, warm and cold water immersion affects the cardiovascular and neuromuscular systems, respectively. Nine articles focused on the effects of warm water immersion, explaining its thermal effect in relation to changes in disease-related serum substance levels and hemodynamic changes. While the sample population in most studies comprised young adults, two articles applied partial water immersion to the legs of elderly subjects to assess its effect on sleep. Because the water immersion protocols applied in the 13 articles were inconsistent, the health benefits could not be clearly explained. However, we expect the present findings to be beneficial for providing research guidelines for studies on the application of water immersion.