Fluid requirements vary between individuals. Body contains 62% of weight as water. Adequate hydration is important to maintain body temperature. Blood, lungs, kidneys and heart are made of 80% of water. Muscle, skin, brain and intestines are made of 72 to 75 % of water. Fat tissue is 10% water and even bones are 22% water. An average person needs 8 to 10 glasses of water per day just to replace average losses.

• In normal healthy adult the fluid requirement is around 25 to 20 ml per kg body weight per day.
• Adult 55 to 75 years fluid requirement is 30ml/kg body weight per day.
• Adult greater than 75 year’s fluid requirement is 25 ml/ kg body weight/day.

Fluid requirements for pediatrics-

• Body weight less than 10 kg, 10 ml/kg fluids per day.
• Body weight between 11 and 20 kg 1000 ml per day + 50 ml/kg for each kg and above 20 kg.
• Body weight greater than 20 kg 1500 ml per day + 20 ml/kg for each kg and above 20 kg.

 An increase or decrease in fluid requirement is based on number of factors:

Factors that increase fluid requirement are vomiting, fever, diarrhea, fistula, pressure ulcer, excessive perspiration.
Factors that decrease fluid intake are edema, renal disease, cardiac disease, congestive heart failure, hyponatremia.