Disorders of water homeostasis are common in psychiatric patients and include compulsive water drinking, the syndrome of inappropriate antidiuretic hormone secretion (SIADH), and the syndrome of self-induced water intoxication (SIWI). Although water intoxication was recognized nearly 70 years ago, the physiological basis of these disorders of water metabolism still remains elusive. This review will provide a historical overview, critique current studies on compulsive water drinking and SIWI, discuss possible etiologies, and present current approaches to treatment of these disorders. Because of the complexity of the subject, a review of normal water homeostasis and the SIADH will be included.