You might be drinking water wrong all along: What your body actually needs for hydration, experts reveal

For years, the idea that everyone should drink eight glasses of water a day has been widely promoted as a universal standard for good health. Simple, easy to remember, and often repeated—but according to health experts, it’s also misleading. Mayo Clinic, Healthline, and the National Academies of Sciences points out that hydration needs are highly individual. Factors such as age, physical activity, diet, and climate all play a role in determining how much water a person truly needs. Instead of following a one-size-fits-all rule, experts urge people to listen to their bodies and hydrate based on actual needs.

The Myth of 8 Glasses: Not Backed by Science

Although the eight-glasses-a-day rule is widespread, there is no scientific basis behind it. Healthline notes that this guideline may have originated from a general calculation based on daily caloric intake, but it does not take into account the wide variation in individuals' water needs. The Mayo Clinic explains that daily fluid requirements can differ significantly and often depend on age, weight, lifestyle, and environment.

According to the National Academies of Sciences, men require about 3.7 liters of fluids per day, while women typically need around 2.7 liters. This includes not only water but also fluids from other beverages and food.

Hydration Across Different Age Groups

Hydration needs change with age. Children between 4 to 13 years may need between 1.2 to 2.6 liters daily depending on their activity levels. Teen boys can require up to 3.3 liters and teen girls around 2.3 liters. For adults, women usually need about 2.1 liters, but this increases with exercise or heat. Men generally need approximately 3 liters. During pregnancy and breastfeeding, water needs rise to 2.4 to 3 liters to support both the mother and baby.

Contrary to common belief, hydration doesn’t come from plain water alone. Healthline points out that beverages like milk, juice, tea, and even moderate amounts of coffee and beer can contribute to fluid intake. Foods such as fruits, vegetables, eggs, and meats also contain a high water content. Even metabolic processes inside the body generate a small amount of water.

How to Know If You're Drinking Enough

Rather than sticking to a fixed number of glasses, experts suggest listening to your body. Signs that you’re well-hydrated include pale yellow urine, steady energy levels, and regular urination every 3 to 4 hours. Dry lips, fatigue, headaches, and dark urine may be early signs of dehydration. The Mayo Clinic advises that checking your urine color and paying attention to thirst are effective ways to monitor hydration.

Proper hydration supports various bodily functions. According to Healthline, drinking enough water may assist with weight management, reduce the severity of headaches, support physical performance, prevent constipation, and possibly lower the risk of kidney stones. For athletes or those in hot climates, staying hydrated is especially crucial to avoid fatigue and impaired function.

While the eight-glass rule may be easy to remember, it’s not a universal truth. Health authorities agree that hydration needs are highly individual and can be met through a mix of fluids, food, and internal processes.