Health & Fitness · 体水分率（Body Water） · Updated 2026-10-25
What Is Body Water Percentage?
Definition
Body water % = total body water ÷ weight, roughly 55-65% for men and 45-60% for women (estrogen raises body fat, lowering water share). Muscle is ~75% water while fat is only ~10% — at equal weight, the leaner person shows markedly higher water. Sharp drops follow dehydration, diarrhea or diuretics. Scales estimate it via bioelectrical impedance (BIA): current passes slowly through fat, fast through muscle; error is ±2-4 points, so track the trend, not the absolute number.
Formula
Body Water % = Total Body Water / Weight × 100%
Worked Example
A healthy 70kg man carries ~42L of water (60%); after 3 months of training at unchanged weight but body fat from 25% to 18%, water share rises 55%→60% — direct evidence of added muscle.
Common Misconception
"Higher is always better" — edema (heart, liver or kidney issues; poor circulation from sitting) also inflates the number. And "I drank water and gained 1kg" — short-term intake is gastric content and circulating volume; most is excreted within two hours and does not change body composition.
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