Diabetes insipidus is a medical condition caused when a hormone known as ADH does not appear in your blood. ADH is released from the brain, and travels in the blood to the kidneys. Here, it pulls water out of the urine, which reduces the amount of urine stored in the bladder.
If there is no ADH in the blood, the kidneys leave the water in the urine, and the bladder holds more liquid. This means you need to go to the toilet more often. It also makes you thirsty. Increased thirst and urination are symptoms of regular diabetes (diabetes mellitus). That's why diabetes insipidus shares the name "diabetes."