Fig 1 shows that the adult body (70 kg) is composed of approximately 42 L of water (approx 60 %). We can further split the 42 litres into respective compartments:

• 28 litres is intracellular fluid (ICF)
• 14 litres is extracellular fluid (ECF)

Chart 1 shows a Pie Chart depicting ICF as 28/42 litres and ECF as 14/42 litres.

We can further split the 14 litres of ECF into its component parts.

Chart 2 shows a Pie Chart depicting ECF is comprised of:

• 10.5 litres is interstitial fluid
• 3 litres is in the plasma
• 0.5 litres is transcellular fluid

From this we can say:

Total Body Water (TBW) = ICF + ECF