The term water retention (also known as fluid retention) signifies an abnormal accumulation of fluid in the circulatory system or within the tissues or cavities of the body. Water is found both inside and outside the body’s cells. It forms part of the blood, helping to carry the blood cells around the body and keeping oxygen and important nutrients in solution so that they can be taken up by tissues such as glands, bone and muscle. Even the organs and muscles are mostly water. The body uses a complex system of hormones and hormone-like substances called prostaglandins to keep its volume of fluid at a constant level. If one were to intake an excessive amount of fluids in one day, the amount of fluid would not be affected in the long-term.