The main function of Vasopressin is to regulate water homeostasis. This talk will focus on new diagnostic and therapeutic options in vasopressin-dependent fluid disorders, i.e. the polyuria polydipsia syndrome on one side, and the syndrome of inappropriate antidiuresis (SIAD) on the other side. Specifically, the difficulties and limitations in diagnosis of polyuria polydipsia syndrome will be mentioned and a new diagnostic algorithm based on copeptin, the c-terminal part of the AVP prohomone, will be shown. In SIAD, new treatment options are needed, since fluid restriction is only successful in about 50% of patients and other options such as vaptans or urea are either very expensive or have a rather low compliance rate. In this talk, I will show data for SGLT-2 inhibitors in the treatment of patients with SIAD.