Overhydration is much more common in people whose kidneys don't excrete water normally, such as those with heart, kidney, or liver disease. People with these problems may have to limit the amount of water they drink and the amount of salt they ingest. As with dehydration, the organ most susceptible to overhydration is the brain. When overhydration occurs slowly, the brain cells have a chance to adapt, so very few symptoms occur. When overhydration occurs quickly, a person can develop mental confusion, seizures, and coma.
Doctors try to distinguish between overhydration and excess blood volume.
With overhydration, excess water is found both within and around the cells and doesn't generally result in signs of fluid accumulation. With excess blood volume, the body also has too much sodium and therefore can't shift water into the reservoir within cells. In conditions of volume overload, such as heart failure and cirrhosis of the liver, fluid accumulates around cells in the chest, abdomen, and lower legs. Distinguishing between overhydration and excess blood volume is often quite complicated, as overhydration can occur by itself or along with excess blood volume. The treatment of overhydration depends to some degree on the underlying cause.