Answer: kidney
Kidneys are the part of the excretory system of the animal body including human beings. Kidneys are the two organs which collectively act as a natural filter to filter out wastes from the body and helps in the regulation of the blood pressure, red blood cell production and maintaining the electrolytic balance in the body. It expels out unwanted salts, sugars, excess water, urea, ammonia and other wastes from the body.
Therefore, A sudden change in the body’s salt and water balance would most likely be caused by a malfunction in kidney.