What is an excessive urinary output?

More than 3-4 L urin. Normally your body regulates how much water you need.The kidney is capable of eliminating the excess.So simply if you drink more fluids you pas more urine.Excess urine can also result from medications and certain foods.
Polyuria. Excessive urine output is most commonly due to excessive fluid intake. Occasionally due to Diabetes Insipidus (DI) which is not Diabetes Mellitus. DI is due to inability of kidney to re-absorb sufficient filtered water by the kidney. Causes aren 1) inadequate secretion of anti-diuretetic hormone by pituitary gland or 2) due to kidney damage. DI is associated with severe thirst.