Maintenance of normal intracellular fluid volume depends largely on the intracellular concentration of ions.

Water is attracted to ions, such as sodium, potassium, phosphate, and chloride ions. Maintenance of normal intracellular fluid volume depends largely on the intracellular concentration of potassium and phosphate ions. Maintenance of extracellular water volume on the other hand depends primarily on the extracellular concentration of sodium and chloride ions.