Water makes up the largest component of the human body, with total body water comprising 75-80% of body weight in neonates, reducing to 60% by age 1-2. Total body water consists of intracellular and extracellular fluids as its two major compartments, along with two minor compartments of transcellular and slowly exchangeable fluids. Intracellular fluid volume makes up 35-40% of body weight and contains fluid within cells, while extracellular fluid volume comprises 20-25% of body weight as plasma and interstitial water.

1.  Water is the largest component of human body.
Total Body Water (TBW) in full -term neonates is
approximately 75 to 80 % ob body weight and
gradually reduces to 60 % by one or two years of
age .
 Total body water is consists of two major
compartments, i.e. intracellular fluids (ICF) and
extracellular fluids (ECF) and the two minor
compartment , i.e. Transcellular fluids (TCF) and
slowly exchangeable fluids (SEF) compartment

2.  Intra cellular fluids volume represents 35to40 % of
body weight and is the sum-total of fluids from the
cells in different locations.
 Extracellular fluid volume represents 20-25 % of
body weight and consist of plasma water and
interstitial water .
 Transcellular fluids volume represents about 2 % of
body weight , its most important components being
gastrointestinal secretion , urine in kidney and lower
urinary tract , CSF .
 Slowly exchangeable fluid volume represents 8-10 %
of body weight and is contained in bones , dense
connective tissues and cartilages.

3. Fluid compartments Infants Older children
Intracellular fluid
( ICF )
40% 35 to 40%
Extra cellular fluid
(ECF)
35-40% 20 – 25 %
 interstitial - 15%
Transvascular
(plasma)
- 5%
 Transcellular - 1-3 %
Total body water 75-80 % 60%