Water is the most abundant constituent of the human body, accounting for approximately 60 to 70% of the body mass. The total body water is divided into two main compartments, the intracellular water (ICW) and extracellular water (ECW). Osmolality and colloidal osmotic pressure influence the water balance between ECW and ICW. The electrolytes are positively and negatively charged ions present in solution in all body fluids. Sodium is the main ECF cation and potassium is the main ICF anion. Water and electrolyte balance are regulated together by thirst, antidiuretic hormone, rennin-angiotensin-aldosterone system, atrial natriuretic peptide, and kidney. Dehydration and over hydration are the disorders of water and electrolyte balance which occur due to an imbalance of water intake and output or sodium intake and output.