Urine is the watery fluid formed by the organs of the urinary system for the removal of metabolic waste products. In humans and other higher animals, urine is produced by the kidneys, stored in the urinary bladder, and excreted through the urethra.

Apart from water, the main components of urine are end products of nitrogen metabolism – ammonia, urea, uric acid, and creatine. It may also contain various inorganic ions, the pigments urochrome and urobilin, amino acids, and purines.