A low body water percentage usually reflects your body composition, not how much water you drank today. The single biggest factor is your ratio of muscle to fat. Muscle tissue is roughly 70-75% water, while fat (adipose) tissue is about 80-85% triglyceride by mass, with only around 4% extracellular water. So the more body fat you carry relative to lean mass, the lower your overall body water percentage will read, even if you’re perfectly hydrated.
That said, body composition isn’t the only explanation. Age, sex, medications, diet, and even the timing of your measurement can all push the number down. Here’s what’s actually going on.
What a “Normal” Body Water Percentage Looks Like
Body water percentage varies naturally by age and sex. In children aged 3 to 10, both boys and girls sit around 62%. For normal-weight adult men between 21 and 60, the number stays close to that same 62%. Adult women see a drop earlier: body water falls to about 55% during adolescence and holds there through the adult years, largely because of the natural increase in body fat that comes with female puberty.
After age 61, both sexes see a noticeable decline. Men drop to around 57%, and women to about 50%. This is driven primarily by the loss of muscle mass that accelerates in older age. If your reading falls within or near these ranges for your age and sex, your body water percentage is likely normal, even if the number on your scale seems low compared to a generic “60% of the body is water” benchmark.
Body Fat Is the Most Common Reason
Because fat tissue holds so little water compared to muscle, body fat percentage is the strongest predictor of where your body water reading lands. Obesity tissue has been estimated at roughly 64% fat, 32% cell residue, and just 4% water. Compare that to muscle, which is predominantly water by weight.
This means two people of the same height and weight can have very different body water percentages if one carries more muscle and the other carries more fat. It also means that gaining fat without gaining muscle will push your body water reading down, even though you haven’t become dehydrated in any meaningful sense. If your scale shows a low body water percentage alongside a high body fat percentage, the composition of your body is the explanation, not your fluid intake.
Age-Related Muscle Loss
The gradual loss of muscle tissue that begins around middle age and accelerates after 60 is one of the main reasons body water percentage drops with aging. Research tracking body water from childhood through old age found that both sexes showed a steady decline in the over-61 age group, falling to 57% in men and 50% in women. The authors attributed this directly to reduced muscle mass. If you’re noticing your body water percentage trending downward over the years, this is the most likely explanation, and resistance training is one of the most effective ways to slow or partially reverse it.
Temporary Dehydration vs. Long-Term Composition
It’s worth separating two different things that can both look like “low body water.” One is your baseline body water percentage, which is a reflection of your body composition and changes slowly over months or years. The other is acute dehydration, which is a short-term loss of fluid that can happen in hours.
True dehydration means your body has lost water faster than you’re replacing it. Clinically, this produces a rise in the concentration of your blood, pulling water out of your cells to compensate. You’ll feel it: dark urine, dry mouth, thirst, fatigue. Severe dehydration brings more alarming signs like dizziness, rapid heartbeat, confusion, sunken eyes, and skin that doesn’t bounce back when pinched. That’s a medical emergency.
A chronically low body water percentage on your bathroom scale, on the other hand, is almost never an emergency. It’s telling you something about how your body is built, not that you’re in danger. The two problems have different causes and different solutions.
Medications That Lower Body Water
Certain medications actively increase the amount of water your body excretes. Diuretics, often prescribed for high blood pressure or heart failure, are the most obvious example. Their most common side effect is mild fluid volume loss, which can show up as increased thirst and slightly lower body water. In cases of over-treatment, the fluid loss can become significant enough to cause low blood pressure, dizziness, or fainting.
Some newer diabetes medications work by forcing excess glucose out through the urine, which pulls water along with it through osmotic effects. Blood pressure medications that block the body’s salt-and-water retention system can have a similar, milder diuretic action. Even alcohol at higher concentrations (above about 13.5%) temporarily suppresses the hormone that tells your kidneys to hold onto water, creating a short-lived increase in urine output. If you’re taking any of these medications and seeing low body water readings, the drug is a likely contributor.
How Diet Affects Water Retention
Your diet influences how much water your body holds onto at any given time, sometimes in counterintuitive ways. Higher salt intake actually causes the body to conserve water rather than lose it. In controlled studies, increasing salt intake by 6 grams per day reduced the amount of free water the kidneys excreted by about 540 milliliters daily. The body essentially hoards water to keep its internal salt concentration balanced. So a very low-sodium diet could, paradoxically, mean your body retains less water than usual.
Carbohydrate intake matters too, though through a different mechanism. Your muscles store carbohydrates as glycogen, and each gram of glycogen binds several grams of water. When you cut carbs sharply, as on a ketogenic or very low-carb diet, your glycogen stores deplete and the water bound to them is released. This is why low-carb diets produce rapid initial weight loss that’s mostly water. It also means your body water percentage can drop noticeably in the first week or two of carb restriction.
Your Scale May Be Reading Incorrectly
Most home scales estimate body water using bioelectrical impedance analysis, or BIA. The scale sends a small electrical current through your body and measures the resistance. Since water conducts electricity well and fat does not, higher resistance suggests more fat and less water. It’s a reasonable estimate, but several factors can throw it off.
The National Institutes of Health recommends avoiding BIA measurements when you’re dehydrated, within 4 hours of eating or drinking, when you have a full bladder, or within 12 hours of moderate to strenuous exercise. Dehydration in particular can skew results, and women appear more susceptible to measurement error than men: in one study, 59% of women showed a body fat difference greater than 2 percentage points when dehydrated, compared to just 9% of men. Individual readings occasionally varied by more than 5 percentage points from control values.
For the most consistent readings, step on the scale at the same time each day, ideally in the morning after using the bathroom but before eating or drinking. Even then, treat the number as a rough trend indicator rather than a precise measurement. If you measured once and got a low number, try again under better conditions before drawing conclusions.
How to Raise Your Body Water Percentage
If your low reading is driven by body composition, drinking more water won’t change it. Your kidneys are remarkably efficient at excreting excess fluid, so chugging extra glasses will mostly just send you to the bathroom more often. The meaningful change comes from shifting the ratio of lean tissue to fat tissue. Building muscle through resistance training increases the proportion of your body that’s water-rich. Losing excess body fat removes tissue that’s water-poor. Both move the needle on body water percentage in a way that simply drinking more cannot.
If temporary dehydration is the issue, the fix is more straightforward: replace the fluid you’ve lost. Spread your water intake throughout the day rather than drinking large amounts at once. If you’ve been sweating heavily, replacing electrolytes (sodium and potassium, primarily) helps your body actually retain the water rather than just passing it through.
For people on diuretics or other medications that increase fluid loss, the solution isn’t to stop your medication. Instead, talk to your prescriber about whether your dose needs adjustment, especially if you’re experiencing symptoms like persistent dizziness or excessive thirst. And if you’ve recently started a very low-carb diet, understand that the initial drop in body water is expected and will stabilize as your body adapts over a few weeks.