The human body is approximately 70% water by content, with most of that water contained within cells and skeletal muscle mass.
"So I think most people will probably understand we're about almost 70% by content water, and most of that water is inside our cells, and a lot of is inside muscle mass." (said at 0:02:07)
Total body water in healthy adults typically ranges from 50% to 60% of total body weight (averaging approximately 60% in adult males and 50–55% in adult females, though fat-free/lean mass itself is approximately 73% water). The claim is accurate that the majority of body water resides intracellularly (intracellular water comprises roughly two-thirds or ~60–65% of total body water) and that skeletal muscle tissue represents the largest reservoir of this fluid.
- context: Relationship between body water distribution and sarcopenia in older adults: a systematic … (European review of aging and physical activity : official journal of the European Group for Research into Elderly and Physical Activity 2026)
"The results indicated that the proportions of extracellular/total body water (ECW/TBW) and extracellular/intracellular water (ECW/ICW) are associated with sarcopenia, muscle strength, loss of muscle mass, and physical performance in the older people." (abstract, results, passage verified)
pubmedfull study (doi)