AQP2 and Hypercalcemia: Complete AVP resistance is due to a lack of aquaporin 2‐mediated water reabsorption in the renal collecting duct, which may be due to electrolyte disturbances (hypercalcemia or hypokalemia, renal pathologies, gene mutations in the key proteins vasopressin V2 receptor or aquaporin 2) or secondary to adverse drug effects (e.g., lithium) (2, 3).