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This patient has previously unrecognized diabetes insipidus. Polyuria is defined as urine output of more than 3 L daily. Since the body needs to excrete nearly 10 mOsm of solute per kilogram daily, one can quickly determine whether the diuresis is a solute or water diuresis. A water diuresis would suggest diabetes insipidus. Solute diuresis may be secondary to renal functional disorders or may be appropriate with massive amounts of retained solute (postobstructive renal failure). Repletion of the free water deficient is mandatory, and when the patient is able to take oral liquids, he should be able to keep up with his water losses.