The information that we offer is of general nature at best and as such this cannot replace the advice of your doctor.
Occurs when the effect of vasopressin is inhibited by abundant fluid intake. Today it is called primary polydipsia and most often is caused by an abnormality in central regulation of thirst, located in the hypothalamus.
It is very difficult to differentiate from the DI pituitary, since both disorders may arise from the same brain disorders.
Reference
The Diabetes insipidus Foundation, Inc. - www.diabetesinsipidus.org