Few health recommendations have achieved the ubiquity of the “eight-glasses-a-day” rule. It’s simple, memorable, and sounds reasonable. But it turns out this decades-old guideline isn’t rooted in science—and may even be misleading for millions trying to stay hydrated.
Emerging evidence from medical and nutritional research shows that hydration needs vary widely between individuals, depending on lifestyle, diet, health status, and climate. Yet, oversimplified advice continues to dominate headlines and health apps alike.
Drinking water from the well left by Sunan Ampel is believed to be able to cure all kinds of diseases among the people. Credit: Shutterstock
Now, experts are pushing back. They argue that rigid, one-size-fits-all hydration goals ignore how the body actually regulates fluids—and risk encouraging harmful overconsumption. The scientific community is calling for a more flexible, evidence-based approach to daily water intake that reflects the full spectrum of personal and physiological factors.
What the Real Science Says About Daily Hydration
The most authoritative benchmark for hydration comes from the National Academies of Sciences, which published detailed intake guidelines in its Dietary Reference Intakes report. The figures are precise:
3.7 liters per day for men
2.7 liters per day for women
These totals represent all sources of fluids, not just drinking water. That includes other beverages—like tea, coffee, and juice—as well as moisture from food, which typically accounts for about 20 percent of a person’s daily intake.
Despite this comprehensive data, the eight-glass rule (roughly 1.9 liters) continues to circulate, often without context. It fails to reflect how fluid needs fluctuate based on heat exposure, exercise, illness, and even dietary composition.
Urologist Dr. Rena Malik, in a widely viewed explainer video for Men’s Health, breaks down the misunderstanding. “Twenty percent of our fluids come from our food,” she explains. “You need to be having some form of fluids in that volume a day.”
In short, the human body pulls water from many sources—not just from what’s poured into a bottle. Hydration is more about total fluid balance than hitting a daily minimum of pure water.
Overhydration Is Not Harmless
A less discussed—yet serious—issue is overhydration. While under-drinking is a common concern, drinking too much water, especially in a short time, can be dangerous.
Dr. Malik warns that excess fluid can dilute sodium levels in the bloodstream, leading to hyponatremia. “Sometimes if you drink too much, it can lower the salt in your body too much and cause something called hyponatremia, which can make you very sick,” she says.
Hydration is not about reaching a magic number. It’s about maintaining balance—across inputs, outputs, and individual variables. Credit: Shutterstock
This condition, though rare, is well-documented among endurance athletes, military trainees, and individuals aggressively hydrating without understanding their electrolyte needs. It can cause symptoms such as nausea, headache, confusion, and in severe cases, seizures or coma.
Still, hydration advice often focuses only on increasing water intake, without addressing variables like body weight, sodium loss, or urinary output—all of which impact fluid balance. There’s growing concern among health professionals that blanket recommendations to “drink more water” may be causing more confusion than clarity.
Your Hydration Comes From More Than Water
One major misconception about hydration is that it’s strictly about what you drink. But what you eat plays a larger role than most people realize. Fruits, vegetables, soups, and yogurt are all high in water content and significantly contribute to total hydration.
In fact, individuals on diets rich in whole, fresh foods may need fewer beverages than those eating mostly dry or processed foods. The body efficiently extracts moisture from food sources, reducing the need for additional water—especially in sedentary conditions.
This is why fixed water quotas are largely arbitrary. A 90 kg athlete training outdoors in summer has vastly different fluid needs than a 60 kg office worker eating high-water-content meals indoors.
Dr. Malik notes another overlooked insight: concentrated urine can irritate the bladder, causing frequent urges to urinate. “Drinking too little water makes your urine very concentrated. That concentrated urine can actually act like a bladder irritant,” she explains. Paradoxically, some people may experience more urgency when they drink too little, not more.
Signs Your Body Already Knows What It Needs
Rather than obsess over numbers, health professionals suggest paying attention to physiological cues. Urine color is widely considered the most reliable hydration indicator: light yellow is optimal, while dark amber may suggest dehydration.
Thirst, too, remains a useful—if slightly delayed—signal. Malik emphasizes that the body doesn’t typically register thirst until it has already lost about 2 percent of its water content. That might sound minimal, but even mild dehydration can affect concentration, mood, and physical performance.
Still, this delay doesn’t mean you need to chug water at all hours. The body is well equipped with internal regulatory systems that manage hydration through hormonal and neurological signals. Instead of chasing external targets, many experts encourage tuning in—not just topping up.
People with specific health concerns, like urinary tract infections or kidney stones, may need different hydration goals. But for most healthy adults, the message is simple: drink consistently, eat water-rich foods, and listen to what your body’s telling you.