How Much Water Should I Drink in a Day?

Just like “an apple a day,” we’ve always been told to drink eight glasses of water a day. Yet, this age-old advice may not be accurate after all.

Sure, water is important – it’s actually considered a nutrient. But now scientists are taking a closer look at this nutrition mandate.

The original source of this water myth was a 1945 recommendation from the Food and Nutrition Board of the National Research Council that encouraged adults to consume 2 liters, which translates to eight 8-ounce glasses of water daily.

Yet this “8 x 8” daily water recommendation referred to total intake of water, which includes the water in food and other beverages like milk, juice, coffee and tea. It has been misinterpreted to mean people should drink eight cups of plain water every day.

The confusion has persisted for decades, and now it’s common for people to sip on water all day – often in their trendy 30-ounce Stanley or Yeti tumbler. You can also buy a 64-ounce water bottle adorned with time markers to remind you to drink eight cups of water throughout the day.

Bottled water companies have helped to propagate this “8 x 8” water rule, says Tamara Hew-Butler, an associate professor of exercise and sports science at Wayne State University who has studied the problem of overhydration and how drinking too much water affects the body.

“The analogy to refute the claim that everyone in the world needs to drink exactly eight glasses of water per day would be the corollary that everyone in the world needs to eat exactly 2,000 calories a day to maintain health,” she says. “For food and fluids, one size does not fit all, since smaller and more sedentary people require less calories while larger more active people require more calories to meet their metabolic requirements. Food and fluid intake is driven by food and fluid output – not the other way around, says Hew-Butler.”

While water is important for our health, the benefits of consuming large amounts of water have been overblown. For instance, drinking extra water alone will not help you lose weight unless water intake replaces high-calorie, sugary drinks or it helps you feel full before meals, says Hew-Butler.

Also, don’t expect drinking more water to “flush out” the toxins, she adds.

Most of the time, the kidneys can successfully compensate for drinking more water. You’ll just need to make more bathroom runs. However, Hew-Butler believes drinking extra water is wasteful in this era of global warming.

Even so, water is a hard-working nutrient that plays many roles in keeping us healthy. Drinking adequate amounts of water can prevent dehydration – a condition that can result in fatigue, confusion and overheating. Water helps your body:

Studies suggest drinking more water may reduce kidney stone formation in people with a history of kidney stones and decrease the number of bladder infections in people who often suffer from bladder infections.

Being adequately hydrated is also associated with a significantly lower risk of developing chronic conditions, such as heart and lung disease, and living longer compared to people who do not get sufficient fluids, according to a National Institutes of Health study published in the journal eBioMedicine.

For some people, fewer than eight glasses a day may be enough. Yet others may need even more water, says registered dietitian Christine Rosenbloom, nutrition professor emerita at Georgia State University and co-author of “Food & Fitness After 50.”

Age: “As we age, staying well hydrated can become more challenging because our kidneys don’t conserve water as well as they did when we were younger, and our thirst may not match our need to drink fluids,” says Rosenbloom.

Body weight: People who weigh more have higher water needs.

Climate: Hotter temperatures can lead to water loss through sweating. Living in a warm climate can contribute to dehydration if you’re not paying attention to fluid intake, she says.

Overall health: “Illness, even the common cold or flu, can increase fluid loss and depress the desire to drink,” says Rosenbloom. More water is needed when you have a fever, vomiting or diarrhea.

So what’s the best way to increase total water intake? “Generally, most liquids except shots of hard liquor count, including coffee, tea and sodas,” says Rosenbloom.

Studies have now shown that caffeinated beverages are not a diuretic like previously believed. In other words, they do not increase urinary water losses, says Hew-Butler. When a cup of coffee was tested against a cup of plain water, an equal amount of water was lost as urine, she says. So that means, drinking caffeinated beverages counts as fluid since the body just sees the fluid and the kidney is not affected by caffeine.

However, drinking alcoholic beverages enhances urinary water loss, says Hew-Butler. “Even though the body ‘sees’ and can use the fluid from alcoholic beverages, there is enhanced urinary excretion from drinking alcohol. Therefore, if rehydration is the primary goal, alcohol alone should not be the beverage of choice.”

Water has gotten fancy and there’s no shortage of fortified waters available today – all part of the growing functional beverage market. Some of the biggest water trends for 2023 include collagen and protein waters, and waters to support immune health, mental wellness and sleep.

“Water is water, whether found in your kitchen tap or an expensive bottled water,” says Rosenbloom. “Drink whatever tastes good to you but remember there are no magic health properties in alkaline waters, vitamin waters or other new flavored waters on the market. If you like it, can afford it and you will drink it, go for it!”

It’s important to remember that roughly 20% of our daily fluid intake comes from foods, says Carolyn O’Neil, an Atlanta-based registered dietitian nutritionist and cookbook author.

Fruits and vegetables are especially high in water and can contribute to your total water intake, she says.

As its name states, watermelon is full of water. This warm weather favorite is one of the most hydrating foods you can eat, clocking in at 92% water. Watermelon – along with other fruits and vegetables – is also a good source of the mineral potassium, which is an essential electrolyte needed for fluid balance, blood pressure control and heart health.

“All of those summer salads and fresh fruit desserts can help you stay hydrated,” says O’Neil. “Fresh fruit adds incredible flavor and juiciness to green salads. Add in-season summer peaches, blueberries and strawberries to salads, yogurt and fresh fruit salsas to top grilled meats and fish.”

Yes, it’s possible to get too much of a good thing. People can (and do) die from drinking too much water, says Hew-Butler.

When people drink too much water at once (that is, more water than they can excrete), the excess fluid dilutes the sodium levels in the blood. The clinical condition is called hyponatremia, and it can be life-threatening, she says.

This causes all the cells and organs of the body to swell through an osmotic process. People can die from water intoxication because the brain can swell so fast that it pushes the brainstem out of the skull. This can also happen in hospitals when too much intravenous or IV fluids are given at once. But it’s also a concern at IV bars, or Drip bars, which are non-hospital establishments offering IV hydration and vitamin treatments, that seem to be popping up in urban areas, says Hew-Butler.

While most people will not likely die from overdrinking, there are more minor complications from excess water including a stretched-out bladder, says Hew-Butler. “When this happens, the bladder muscles can no longer force the urine out with each void and residual urine remains in the bladder, which can also ’back-up’ into the ureters and kidneys and cause problems.”

If you stick with eight glasses of water a day, you’ll be fine. But there is no need to stress if you don’t achieve this every day. Also, do not overlook the contributions of other beverages and foods, especially soups, smoothies, coffee drinks, teas and water-dense fruits and vegetables.