Polyuria is the production of abnormally large volumes of urine, generally defined as more than about 2.5 to 3 litres per day in adults. It results from osmotic diuresis, as in uncontrolled diabetes where glucose drags water into the urine, from diabetes insipidus where antidiuretic hormone signalling fails, or from high fluid intake, diuretic drugs, and kidney disorders. The companion symptoms of polydipsia and polyuria together are the classic presentation of new-onset diabetes mellitus and should prompt urgent glucose testing. Nutritionally, polyuria wastes water, sodium, potassium, and magnesium, requiring replacement, and the underlying hyperglycaemia demands dietary management alongside medication. Distinguishing true polyuria from frequent small-volume urination of bladder irritation or prostate disease guides the diagnostic path, since the causes and treatments differ completely.