During the day, your kidneys filter all your blood many times. Normally, most of the water is reabsorbed, and only a small amount of concentrated urine is excreted. DI occurs when the kidneys cannot concentrate the urine normally, and a large amount of dilute urine is excreted.

The amount of water excreted in the urine is controlled by antidiuretic hormone (ADH). ADH is also called vasopressin. ADH is produced in a part of the brain called the hypothalamus. It is then stored and released from the pituitary gland. This is a small gland at the base of the brain.

DI caused by a lack of ADH is called central diabetes insipidus. When DI is caused by a failure of the kidneys to respond to ADH, the condition is called nephrogenic diabetes insipidus. Central diabetes insipidus can be caused by damage to the hypothalamus or pituitary gland as a result of:
-- Genetic problems
-- Head injury
-- Infection
-- Loss of blood supply to the gland
-- Surgery
-- Tumor

Nephrogenic DI involves a defect in the kidneys. As a result, the kidneys do not respond to ADH. Like central DI, nephrogenic DI is very rare. Nephrogenic DI may be caused by:
-- Certain drugs (such as lithium)
-- Genetic problems
-- High level of calcium in the body (hypercalcemia)
-- Kidney disease (such as polycystic kidney disease)