A disease characterized by excretion of large amounts (hence the allusion being that "water passes through them like a siphon") of severely diluted (i.e., "tasteless") urine, which cannot be reduced when fluid intake is reduced. There are four types of diabetes insipidus (DI), each with a different set of causes. Central DI is due to a lack of vasopressin (antidiuretic hormone) production. This can be due to injury to the hypothalamus or pituitary gland or genetics. Nephrogenic DI occurs when the kidneys do not respond properly to vasopressin. Dipsogenic DI is a result of excessive fluid intake due to damage to the hypothalamic thirst mechanism. It occurs more often in those with certain psychiatric disorders or on certain medications.Gestational DI occurs only during pregnancy. Diagnosis is often based on urine tests, blood tests and the fluid deprivation test. Diabetes insipidus is unrelated to diabetes mellitus and the conditions have a distinct mechanism, though both can result in the production of large amounts of urine.