I ‘M NOT FEELING so good,” YouTuber Chef Boy-R-G said halfway into his #gallonchallenge.

The aspiring social-media star was trying to drink a full gallon of water—128 ounces—in a single sitting, and things weren’t going well. His lips drooped, guppy-like, and he leaned out his driver-side door. “Chef Boy-R-G just threw the f—k up,” he said after regaining his composure. “F—k this water.”

F—k water? Someone has a bad thing to say about water? We’re living in the era of peak hydration, a time when toting a gallon jug around an air-conditioned gym doesn’t warrant a second look and crowds wait hours for the latest 40oz Stanley bottle drop. In our search for health optimization, apps tally our daily ounces and Stanford professor Andrew Huberman’s two-hour-and-22-minute podcast episode “How to Optimize Your Water Quality & Intake for Health” nets 1.2 million views on YouTube. Online, #WaterTok has notched a billion-plus views on TikTok in barely a year. Water is seriously trending.

But our hydro-obsession can put us on a slippery slope. Thousands of those #WaterTok videos extol the virtues of water fasting—consuming nothing but flavored water—and powering through a gallon each day. Water influencers (which, yes, are a thing now) flood our feeds with misinformation—Drink eight glasses a day! No, drink an ounce for every pound you weigh!—while bro science—Excessive water consumption flushes out toxins!—surges. The high-water line of H2O’s toxic trendiness may have come late last year, when the actress Brooke Shields turned blue, began frothing at the mouth, and collapsed at a New York restaurant. The culprit? Excess water caused her sodium levels to plummet, leading to a seizure. “I don’t think people understand: Drinking too much water is not safe and can result in serious complications such as seizures, brain swelling, and even death,” says Robert Glatter, M.D., an assistant professor of emergency medicine at Lenox Hill Hospital who has treated people who’ve landed in the ER due to water fasts. “Most people think more is better, but that’s not true.”

Water, water everywhere, especially on TikTok. The ubiquity of the posts, the bottles, and the mentions has helped turn this basic giver of life into a seriously trendy topic.

In the span of a generation, water has gone from boring but necessary to a style statement to the vessel in which we place our wellness hopes and dreams. How did we end up so hydro-hysterical? The science of hydration isn’t so cut-and-dried, especially when it comes to the research on the amount of water you need to perform optimally versus to simply survive. Optimum hydration is new and understudied, and it turns out—hold on to your Yeti—the world’s leading hydration researchers disagree on how much water we should be drinking and when we should be drinking it. But new research gives us the insights we need in order to ensure we’re not drinking too little and also not drinking too much. To understand how we arrived at this watershed moment, we need to rewind to the first stubborn water myth: the advice to drink eight 8oz glasses of water per day.

IT’S EASY TO forget that water doesn’t just power your workouts. All life on earth evolved to depend on the miraculous bond between hydrogen and oxygen atoms. When scientists say that the human body is made up of 60 to 75 percent water, it’s not because we’re storing it for a potential marathon. It’s because our bodies—all living creatures’ bodies, actually—use water molecules to do an incredible variety of work. Water helps cells absorb critical nutrients like sodium; it makes up the vast majority of blood, which transports oxygen and other necessary molecules throughout your body. (Without water, funnily enough, you couldn’t breathe.) It sustains us in less direct ways, too: It’s a crucial component of photosynthesis, the mechanism by which plants create oxygen and promote nearly all of the conditions that make our little planet habitable. Water, plainly, is life.

But even though we need it to live, our relationship with water has always been mixed and our views on hydration tainted by myth and superstition. Roman soldiers added spoiled wine and herbs to their H2O to kill bacteria and, they believed, quench thirst. Many early Americans “believed water unfit for human consumption” because of waterborne disease, the historian W. J. Rorabaugh wrote in The Alcoholic Republic, his history of American drinks. For athletes, even into the 20th century, the advice was to abstain from the stuff. “Don’t get in the habit of drinking and eating in a marathon race,” the head of the Amateur Athletic Union wrote in his 1909 book, Marathon Running. “Some prominent runners do, but it is not beneficial.” A few decades later, the most stubborn water myth of ’em all—the one everyone from your grandma to your gym bro still trots out—was born: eight glasses a day.

“You hear it all the time; it’s so pervasive,” Tamara Hew-Butler, Ph.D., an associate professor of exercise and sports science at Wayne State University, says of the idea that we all should drink eight glasses of water per day. But, she says, the recommendation isn’t based in science. In fact, a 2022 Science paper determined that the advice isn’t backed by any evidence at all.

“Some people think I’M A SCAREMONGER,” says sports scientist Tamara Hew-Butler, Ph.D. But she’s DEADLY SERIOUS. “You don’t have to drink THAT MUCH WATER,” she says, any trace of levity dropping from her voice.

So where did it come from? As best we can figure, the idea that everyone across the board should do 8×8—eight 8oz glasses per day—dates either to an offhand suggestion from the eminent mid-century nutritionist Frederick Stare or to a 1945 recommendation by the U. S. Food and Nutrition Board, which figured that all Americans ought to consume a milliliter of water per calorie eaten, totaling about 64 ounces. Most readers ignored the board’s next sentence, though, which noted that much of this water can come from the foods you eat, like fruits and veggies. “People still don’t understand that there’s also water in food, in soups, tea, coffee,” Hew-Butler says. “All of that counts.”

Yes, including coffee and tea.

Although most of us grew up confident that caffeinated drinks are diuretics—i.e., they make you pee—caffeine does not, in fact, compel you to expel more than you take in. “The dehydration effect happens when you have very high consumption, like 400 milligrams of caffeine—and a regular cup of coffee is about 100 milligrams,” says Stavros Kavouras, Ph.D., a professor of nutrition at Arizona State University and the founder of its Hydration Science Lab. “Coffee is rich in antioxidants and flavonoids, too. If you remove it from people’s diets, you are removing a significant amount of antioxidants from people’s diets.” (You heard it here. Parched? Grab an Americano.)

But if drinking eight glasses a day isn’t evidence based, how much should we consume?

Well, that depends on your activity level, your diet—and whom you ask.

The hydration world is divided. “There are two hard schools,” says Kavouras. He and his cohort believe fervently that a large chunk of the population is walking around underhydrated and that this could have dire health effects, from the expected—diminished athletic performance and brain fog—to the frightful—cognitive decline, kidney damage, and more. The problem, then, is a lot bigger than failing to PR on your next race: “People who are suboptimally hydrated have a higher risk for chronic disease,” he says.

Those on the other side of the divide scoff. The risks of mild dehydration are overstated, they say, and pale in comparison with the risks of something few of us ever consider: drinking too much water. “Some people think I’m a scaremonger,” says Hew-Butler. But she’s deadly serious. “You don’t have to drink that much water,” she says, any trace of levity dropping from her voice.

To really understand the overhydration-phobes and why they care so passionately about thirst, you have to go back two decades, to a spate of mysterious ailments that left athletes dead and shocked the running world.

ART SIEGEL,M.D., has been studying marathoners for as long as anybody. After he got back from Vietnam, Dr. Siegel, who specializes in internal medicine, joined the staff at McLean Hospital, outside Boston, and became an associate professor at Harvard. He also ran, avidly, and had dreams of completing the country’s most prestigious road race. “I had a 3:21 at the Ocean State Marathon in 1977, but you needed a 3:00 to be invited to the Boston Marathon in those days,” he recalls. There was a loophole, however: The marathon invited the fastest doctors around town, so long as they volunteered their medical expertise. Dr. Siegel ran about 15 marathons in Boston, then “retired to the medical tent,” where he would spend the next 30 years treating ailing runners. That’s where he was in 2002 when a 28-year-old runner named Cynthia Lucero, a name he still recalls readily, crumpled and fell on mile 23. “She collapsed in Cleveland Circle,” Dr. Siegel remembers, “and by the time she got to the Brigham”—Boston’s famed Harvard-associated hospital—“she had died a brain death.”

Nobody was tracking deaths at marathons in those days. But a few years earlier, Hew-Butler had been volunteering at the medical tent at the Houston Marathon, where the oppressive heat compelled runners to guzzle tons of water. “Four runners collapsed, and everybody thought they were dehydrated,” Hew-Butler says. “The medical team gave them up to four IVs” of fluid—the standard treatment for someone severely dehydrated. “Then they had seizures and they had to be intubated in the med tent, and then they were in comas for a week.” The runners survived, Hew-Butler says. “Then it came back that they were all hyponatremic—and we were all like, what is that?”

As recently as 2002, experts didn’t realize that marathoners collapsed and sometimes died from overhydration, not just dehydration.

Back in Boston, Dr. Siegel had heard murmurs about these cases, and on a hunch, he made a call to the attending he knew at Brigham. He got permission from Lucero’s family to do a blood test. The results made nationwide news. She had died of exercise-induced hyponatremia: water poisoning.

Hyponatremia is, technically, an imbalance of the sodium and water in your blood. (It’s also what Brooke Shields suffered from at the New York restaurant late last year.) Sodium, despite our fear of the salt shaker, is what maintains a healthy blood pressure and keeps all your muscles and nerves moving in concert. When the concentration of sodium—a key electrolyte—in your blood nose-dives, everything goes haywire. Nausea and weakness come first, then confusion sets in, followed by seizures and finally unconsciousness and death.

The deaths of marathoners convinced Dr. Siegel, Hew-Butler, and a small coterie of other hydration experts to obsess about overhydration. Dr. Siegel’s colleagues took blood samples at the finish line in Boston, and it turned out that a significant number of marathoners—a full 13 percent—were hyponatremic. The research also showed that electrolyte loss (i.e., sweating out too much salt) wasn’t the primary cause of hyponatremia, either. In fact, Lucero, the runner who died in Boston, drank mostly Gatorade. The condition is simply brought on when runners drink way, way more water than they sweat out.

Today, thanks to the work of these specialists, collapsed runners at the Boston Marathon medical tent are tested for dehydration and hyponatremia. For Dr. Siegel and others who’ve spent the better part of two decades on this work, the way to avoid hyponatremia—and the secret to adequate hydration—is straightforward: Don’t drink so much water.

“Thirst is a tremendously accurate sense,” he says, one that has been honed over millennia of human evolution to keep our bodies in perfect balance. Ignore the hype, his half of the hydration world argues, and keep it simple. Just drink when you’re thirsty. Athletes who don’t, Dr. Siegel warns, run a serious risk. “The message has to be: Drink only to thirst,” he says.

Too bad most of us have no idea how much to drink when we seriously exert ourselves—and society seems hell-bent on convincing us to guzzle even more.

AS DR. SIEGEL and others in the hydration world urged drinkers to tone it down in the early 2000s, water began to take on a strange new aura: status symbol.

Health and fitness in the new millennium are what wealth was in the ’80s—something to flaunt. And water bottles have evolved into a great way to accomplish this. In the ’90s and 2000s, when we toted our dusty Nalgenes from the trail to the college dorm, we told everyone something about ourselves. I’m an active person, our reusable jug said, and I’m helping save the planet, because I’m not about to buy a single-use plastic bottle. Then, in 2010, S’well, the maker of those hip metal reusable bottles, hit the scene. All of a sudden, a water bottle signaled not only your virtue but also your style. From S’well, you can draw a straight line to today’s “it” water bottle—the $45, 40oz Stanley sipper that Instagram fell in love with last summer. And if your water bottle is meant to project your virtue and your wellness, the size of it must matter, too. A classic Nalgene was 32oz. Today, Yeti, S’well, and Lululemon all sell gallon bottles.

Hydration became a commodity as well. It’s hard to remember now, but when Pepsi and Coke ventured into the bottled-water business in the 1990s, it was viewed as a lark. These days, bottled water is the most popular beverage in America, its sales surely boosted by water’s halo of health. (In 2022, companies sold more than $40 billion worth of bottled water in the U. S. alone; Americans spent more than $2 billion on reusable bottles, too.) Our fear of dehydration features prominently now in ads for Gatorade and Smartwater.

But as easy as it is to mock the Reddit hydro-homies and the bottled-water corporations, the half of the hydration research field that isn’t working on hyponatremia and doesn’t think we’re overfilling ourselves is thrilled we’re all paying more attention to our ounces. Their message is a simple one: Drink up.

Kavouras is a leading figure in this space. He’s one of the most cited scientists in the country (which is a big deal) and is seriously concerned with the chronically parched. His research suggests that thirst alone does not compel people to drink enough water and, more important, that the long-term effects of dehydration may be making us all sicker.

Most American adults (and children) are underhydrated, he says, and his research has shown that folks who are consistently underhydrated—a less severe state than dehydrated—have elevated blood levels of antidiuretic hormone, which tells the body to conserve excess water. This hormone, Kavouras has found, correlates with obesity, insulin resistance, and kidney issues. These underhydrated people, who rely on their thirst but clearly don’t drink enough water, are at greater risk of developing diabetes and serious or even life-threatening complications related to the disease. “We’re finding more and more data that this hormone is associated with chronic disease,” he says, “plus, of course, quality-of-life issues, like concentration and cognitive function.” Conversely, he’s shown that drinking water boosts mood and cognitive performance and that increased consumption suppresses this antidiuretic hormone, which improves glucose regulation and lowers the risks of urinary-tract infections and kidney stones.

There’s little that’s plain about plain water now. Bottles have moved from functional accessory to status symbol, attached to—and sometimes created by—celebs including Tom Brady, LeBron James, and Jason Momoa.

That’s why he’s a fan of the National Academy of Sciences’ official guideline on hydration, which recommends 3.7 liters of fluid per day for men and 2.7 liters for women—or 127 ounces, just under a gallon, for men and 90 ounces for women (but not chugged all at once). Again, these guidelines are for “all the water molecules you take in, from both food and beverage,” Kavouras says. So since “studies show that most people really consume approximately 80 percent of their water from beverages,” he suggests that men drink about 100 ounces of fluids and that women be on the hook for 67. He notes, though, that these needs most definitely change based on your size, the weather, and your activity level. If you’re a big guy doing yard work in the sun, you may need more; if you drove to your air-conditioned office in your 36S sports coat, you may need less. (In case you’re wondering, this hews pretty closely to Andrew Huberman’s guideline, too: consuming about eight ounces of fluid per hour for the first ten hours you’re awake.)

Kavouras has also studied peak performance and hydration. In small studies, he found that cyclists who drank on a regimen performed better than those who drank to thirst, which would suggest that drinking to thirst leads to underhydration. And even more compellingly, he devised an experiment wherein ten elite cyclists—Kavouras, you might not be surprised to learn, is an avid cyclist—were given body-temperature water through tubes down their noses directly into their stomachs. Since it bypassed their mouths, these athletes couldn’t gauge their own dehydration level, a physical and mental discomfort researchers have long suspected affects performance. In the experiment, cyclists who weren’t quite given adequate water—even though they didn’t know—performed worse than the group given more.

For Kavouras, then, the risks of drinking only when you’re thirsty are real. You perform worse, think worse, and get sicker. “Do you want to survive, or do you want to be in optimal health?”

SO WHERE DOES this leave us?

Water is life, yes, but maybe we don’t have to be quite as obsessed with how much we drink as the influencers on #WaterTok. Look no further than the 2 billion Muslims on earth, many of whom refrain from food and water from sunrise to sunset during the monthlong observance of Ramadan. “The human body is a beautiful vessel,” says former NFL safety Hamza Abdullah. “I think we don’t give ourselves enough credit. Your body can withstand a lot of things.”

Abdullah would know. The devout Muslim played seven seasons of pro ball and observed Ramadan the whole time. During Abdullah’s football career, the holiday, which is a movable fast that follows the lunar calendar, took place smack in the middle of the NFL’s August training camps: double days, in the dog days of summer, against the toughest athletes in the country, without a drop of water. “It took a physical toll on me,” he says. “I was losing eight to 12 pounds a day.” (He drank a ton of Gatorade and Pedialyte at sundown, he says with a laugh.) But Abdullah had the support of his coaches and teammates, and he thought the thirst gave him an edge: “I competed with the best football players fasting. What do you think I can do when I’m eating and drinking?” And with sacrifice came clarity. “Why am I doing this? Because I love this game.”

“For those of us who come back from our THREE-MILE JOGS and immediately down two Nalgenes or tote our Yetis around LIKE SECURITY BLANKETS, the idea of dehydration can sound DAUNTING.”

The point is, you probably don’t have to give in to the hydro-hype. Normal folks going about their normal lives and hitting the gym after work can rely on the old classic: the color of their urine. “You want it to be light yellow, like lemonade, not like apple juice,” says Lindsay Baker, Ph.D., a director at the Gatorade Sports Science Institute. But also: “It shouldn’t be clear,” she adds. Taking a leak every two to three hours means you’re probably well hydrated, Kavouras reckons. “On the other side, if you go to the bathroom every 20 minutes, you’re drinking way above and beyond.” The exception to this is the elderly, whose feedback mechanisms regulating total-body water homeostasis are more likely to be disrupted and could probably benefit from an extra glass or two of water each day, according to exercise physiologist Evan Johnson, Ph.D., at the University of Wyoming.

If you are regularly undertaking intense, multi-hour bouts of training or endurance sports, a hydration plan may serve you well. That way, you won’t be dehydrated or overdrink. (The drink-to-thirst crowd would disagree—but at least this way you won’t be hyponatremic.) The first step is to weigh yourself before an intense, hour-long session. During the workout, track the volume of water you drink. Then weigh yourself afterward and subtract the volume of your drinks: Now you know how much you sweat in an hour in those conditions and how much water you need to drink to replace it and stay hydrated. A hydration plan is especially useful during long races, like marathons, when your thirst response can be blunted, Johnson says. But beware, newbies: Most runners who are hyponatremic after a race are inexperienced and tell researchers they drank at the first signs of discomfort. Other folks who could benefit from a hydration plan are those who can’t drink—or pee—regularly during their jobs, like nurses, teachers, and firefighters.

No need to plug into the hydro-hysteria and lug around bigger and bigger water bottles—unless you really want to. If you still decide to be a carrier, just don’t drink it all at once.

When it comes to sodium, the drink-to-thirst crowd sees little benefit to electrolyte replacement unless you’re a salty sweater, unacclimated to the heat, or competing in hot weather for long periods of time, such as during a 12-hour Ironman. But some research suggests that weekend warriors could benefit from electrolytes from sports drinks or powders after a very rigorous hour of exercise. “You don’t have to have a carbohydrate drink” after your hour-long jog, Johnson advises. “But if you’re trying to PR or exercising at high intensity for longer than 45 minutes, you should have a carbohydrate sports drink with electrolytes during that exercise.”

And finally, when you finish an intense or extended workout, don’t pound all your water at once. Chugging initiates your body’s bolus response—its protection against hyponatremia—and you won’t retain enough of the water to replace what you lost. Instead, sip steadily over the course of a few hours.

For those of us who come back from our three-mile jogs and immediately down two Nalgenes or tote our Yetis around like security blankets, Abdullah knows that the idea of dehydration can sound daunting. That’s why he helps other Muslim athletes around the world plan for their training during Ramadan. The end result, he says, will make you truly appreciate what you have. “If you’ve never fasted, fast for a day and then go drink a glass of water,” Abdullah says. “Man, it is so good.”

You hear that, Chef Boy-R-G and #WaterTokers? Abdullah said a glass, not a gallon.