Body water percentage is the proportion of your total body weight made up of water. For the average adult man, that number is about 60%. For the average adult woman, it falls between 52% and 55%. These figures shift with age, body composition, and other factors, but they represent the baseline most health professionals use.
Typical Ranges by Age and Sex
Newborns carry the most water relative to their size, at roughly 70% of body weight. That percentage gradually declines through childhood and into adulthood, settling around 60% for men and 52% to 55% for women. The gap between men and women comes down to body composition: women typically carry more body fat, and fat tissue holds significantly less water than lean tissue. In older adults, body water percentage drops further as muscle mass decreases and fat tissue tends to increase.
Where the Water Actually Lives
Not all of your body’s water sits in the same place. About two-thirds of total body water is inside your cells (intracellular fluid), while the remaining one-third circulates outside them (extracellular fluid) in your blood, lymph, and the spaces between tissues. This is sometimes called the 60-40-20 rule: 60% of body weight is water, 40% is intracellular fluid, and 20% is extracellular fluid. Blood plasma alone is about 92% water.
Different organs and tissues vary dramatically in how much water they contain. The brain and heart are about 73% water. Muscles and kidneys are even higher, at roughly 79%. Fat tissue holds considerably less water than lean tissue, which is the main reason body composition has such a strong influence on your overall percentage.
What Makes Your Percentage Higher or Lower
The biggest factor is how much muscle versus fat you carry. A very lean, muscular person can have a body water percentage well above 60%, while someone with a higher body fat percentage will trend lower. This is also why the number declines with age: people naturally lose muscle and gain fat as they get older, even if their weight stays the same.
Sex hormones play a role too. Hormonal fluctuations during the menstrual cycle can cause temporary water retention, and pregnancy significantly increases total body water. Sodium intake is another short-term driver. Eating a salty meal triggers your body to hold onto extra fluid, temporarily raising your water weight. Carbohydrate intake has a similar effect because your body stores carbohydrates as glycogen, and each gram of glycogen binds several grams of water.
Why Body Water Matters for Health
Water is involved in virtually every function your body performs: regulating temperature, cushioning joints, transporting nutrients, and flushing waste. When your body water drops even slightly below normal, the effects show up fast. Losing just 1% to 2% of your body weight in fluid is enough to reduce endurance during exercise. At 2%, running performance across distances from 1,500 to 10,000 meters is measurably impaired.
At 5% fluid loss, your capacity for physical work drops by about 30%, and your body becomes much less able to tolerate heat. The threshold for heat-related illness shifts downward, meaning you can overheat at a lower core temperature than you normally would. Severe dehydration, if left untreated, can contribute to life-threatening conditions like heatstroke. People with diabetes, heart disease, or cystic fibrosis may be especially vulnerable.
How Body Water Is Measured
The most accessible way to measure body water percentage is bioelectrical impedance analysis (BIA). This technology sends a small, painless electrical current through your body. Since water conducts electricity well and fat does not, the device estimates how much of your weight is water, lean mass, and fat. Many bathroom scales and handheld devices now include BIA sensors.
BIA is affordable and fast, but it has limitations. Compared to more precise methods like dual-energy X-ray absorptiometry (DXA), BIA devices tend to underestimate body fat by about 3% to 3.4% and overestimate lean mass by 2 to 3 kilograms. Your hydration level at the time of measurement, when you last ate, and even whether you’re standing or lying down can all shift the reading. For tracking trends over time, BIA works well as long as you measure under consistent conditions. For a single highly accurate snapshot, clinical methods are more reliable.
How Much Water You Need Daily
Maintaining a healthy body water percentage comes down to replacing what you lose. The average healthy adult needs roughly 11.5 cups (2.7 liters) to 15.5 cups (3.7 liters) of total fluid per day, with the higher end applying to men. That total includes water from all sources: plain drinking water, other beverages, and food. Fruits, vegetables, soups, and other water-rich foods can contribute a meaningful portion of your daily intake.
Your actual needs depend on how active you are, the climate you live in, and your overall health. Hot weather, intense exercise, illness with fever or vomiting, and high altitudes all increase water loss. Rather than fixating on a specific cup count, paying attention to thirst and the color of your urine (pale yellow signals good hydration) gives you a practical, real-time gauge of where you stand.