Body water compartments
Total body water (TBW) is divided into two main compartments: intracellular fluid (ICF), which accounts for approximately 60% of TBW and exists inside cells, and extracellular fluid (ECF), which makes up the remaining 40% and includes blood plasma, interstitial fluid between cells, and lymph.
TBW as a percentage of body weight is higher in lean, muscular individuals (up to 70%) and lower in those with higher body fat (as low as 45%), because fat tissue contains very little water compared to muscle.