Antidiuretic Hormone (ADH), also known as vasopressin, is a hormone produced by the hypothalamus and stored in the pituitary gland. Its primary function is to regulate the body's water balance by promoting water reabsorption in the kidneys. When the body is dehydrated, ADH levels increase, leading to concentrated urine and reduced water loss. ADH plays a crucial role in maintaining blood pressure and fluid balance. It acts on the kidneys' collecting ducts, allowing more water to be reabsorbed back into the bloodstream. This process helps to prevent excessive urination and ensures that the body retains enough water for essential functions.