This high serum osmolarity stimulates excessive thirst in an attempt to dilute the serum back to normal and provide free water for excreting the excess serum solutes. However, since the patient is unable to concentrate urine to excrete the excess solutes, the resulting urine fails to decrease serum osmolarity and the cycle repeats itself, hence excessive urination. Thiazide diuretics allow increased excretion of Na+ and water, thereby reducing the serum osmolarity and eliminating volume excess.