increased water intake would not lead to hyponatremia unless impairment in water excretion exists. While thiazide diuretics do not inhibit concentrating ability, they do impair diluting ability in several ways15, 26, 34). As mentioned above, they inhibit electrolyte transport at the cortical diluting sites, thereby raising the minimum urinary osmolality34-36). Diuretics may also reduce glomerular filtration rate and enhance reabsorption of Na+ and water in the proximal nephron, diminishing fluid delivery to the distal diluting sites35). Thus, water can be retained independent of serum osmolality. Besides, thiazide-induced volume depletion probably contributes to the genesis of TIH in some cases. Hypovolemia may stimulate the release of vasopressin because non-osmotic vasopressin secretion is very common in normovolemic and hypovolemic types of hyponatremia31).