The human body contains 50-60% water mainly in tissues and cells (e.g. a 70 kg adult carries 35-40 litres of water). Water is one of the components of blood. The blood volume of an adult amounts to 1/12 of the total body weight (e.g. 70 kg adult: 5-6 litres of blood).

Major losses of blood volume (hypovolaemia) due to surgery, an accident with burns, or traumatic injuries, must be corrected immediately by giving infusions with blood volume substitutes and/or electrolytes to avoid organ malperfusion secondary to hypovolemia.