Water makes up about 50 to 75 percent of your body weight, depending on your age, sex, and how much muscle or fat you carry. For the average adult man, that number sits around 60 percent. For the average adult woman, it’s closer to 52 to 55 percent. That means a 180-pound man is carrying roughly 108 pounds of water, distributed across every organ, tissue, and cell.
Why the Range Is So Wide
The single biggest factor driving individual variation is body composition. Lean tissue (muscle, organs, skin) holds about six times more water per unit of weight than fat tissue does. Lean tissue is roughly 70 percent water, while adipose tissue is only about 14 percent water. So two people who weigh the same can have very different total body water if one is more muscular and the other carries more body fat.
This is also the main reason women tend to have a lower water percentage than men. Women generally carry a higher proportion of body fat relative to lean mass. The same logic explains why body water percentage drops with age: older adults gradually lose muscle mass and often gain fat tissue, shifting the ratio downward. Newborns sit at the high end of the spectrum, around 75 percent water, because they have very little body fat and proportionally more lean tissue.
Water Content of Individual Organs
Not every part of your body holds water equally. The lungs are the most water-rich major organ at about 83 percent. The brain and heart are each about 73 percent water. Skeletal muscles and kidneys come in at roughly 79 percent. Even your bones contain some water, though far less than soft tissue. The U.S. Geological Survey compiled these figures from physiological research, and they help explain why dehydration affects thinking, heart rhythm, and physical performance so quickly: the organs that depend most on water are the ones that suffer first.
Where All That Water Sits
About 60 percent of your total body water is inside your cells, in what physiologists call intracellular fluid. This is the water that fills every cell in your body and supports the chemical reactions that keep you alive. The remaining 40 percent sits outside your cells. That extracellular portion includes your blood plasma, the fluid between cells, and specialized fluids like cerebrospinal fluid and the liquid inside your eyes and joints.
Your body constantly moves water between these compartments. When you’re dehydrated, water shifts out of cells to maintain blood volume. When you drink a large amount of fluid, the balance tips the other way. The kidneys act as the main regulator, adjusting how much water leaves your body based on hydration signals from the brain.
How Your Body Cycles Through Water Daily
The average adult takes in and loses about 2,500 milliliters of water per day, close to three quarts. Intake comes from drinking fluids, eating food (many fruits and vegetables are over 80 percent water), and a small amount produced by your cells during metabolism.
On the output side, urine accounts for the largest share at roughly 1.5 liters per day. The rest leaves through your skin and lungs as what’s called insensible water loss: moisture that evaporates from your skin even when you’re not sweating, and water vapor carried out with every breath. You’re usually not aware of this loss, but it adds up. Sweating during exercise or in hot weather pushes total losses significantly higher, which is why fluid needs vary so much from person to person and day to day.
Your kidneys need to produce at least about half a liter of urine daily to flush waste products effectively. Drop below that threshold and waste accumulates in the blood, which is why severe dehydration can damage kidney function relatively quickly.
What Changes Your Water Percentage Over Time
Your body water percentage isn’t fixed. It shifts throughout your life and even throughout a single day. Gaining muscle through strength training increases the proportion of your body that’s water, while gaining fat decreases it. This is one reason athletes often test at 65 percent or higher total body water, while someone with obesity might measure below 50 percent despite weighing more overall.
Hormonal changes also play a role. Fluctuations during the menstrual cycle can temporarily shift fluid distribution, causing the bloating many women notice. Pregnancy increases total body water substantially to support blood volume expansion and amniotic fluid. Aging brings a gradual decline not just because of muscle loss but also because the kidneys become less efficient at conserving water, and the thirst signal weakens, making older adults more vulnerable to dehydration even when water is freely available.
Certain medical conditions, particularly heart failure and kidney disease, disrupt the body’s ability to regulate fluid balance and can cause abnormal water retention or loss. Medications like diuretics directly alter how much water the kidneys excrete. These situations can shift total body water well outside the normal 50 to 75 percent range.