Are You Actually Hydrating Correctly?
How much water do you *really* need to drink to stay healthy? Can you drink too much water? And is coffee dehydrating?
“Stay hydrated” has become the new way to say “stay healthy.” Twitter accounts are created with the sole purpose of reminding you to drink a glass of water. Trendy oversized reusable bottles proliferate on the internet, often with chipper messages like “You’ve got it!” and “Keep drinking!” written on the sides to remind you that you need to gulp down more water. Buzzy hydrating products—juices, various waters and tonics—flood the market, promising optimal hydration along with all its associated benefits.
Aside from those benefits—like improved mental health and cognition, better skin and even higher energy levels—keeping hydrated is a necessity for staying alive. And while clean drinking water is easy to find in many parts of the world, in others—including parts of Canada—not everyone has access to this critical resource. Numerous Indigenous communities in Canada have long-term drinking water advisories in effect—even as neighbouring settler communities have plentiful clean water.
“Water is the most critical nutrient that humans need,” says Stephen Cheung, a professor of kinesiology at Brock University who studies the effects of environmental stressors like hydration and temperature on the human body. “If you don’t drink any water, you would be dead or severely incapacitated in five to eight days.” By comparison, you could survive without any food for up to 70 days.
So, how much water should I drink?
How much water you need depends on a lot of different factors, like your size, activity level, age, sex and diet. The guideline for adults is eight glasses, or two litres, a day, but that doesn’t really hold water in 2022: That standard was developed by the U.S. Food and Nutrition Board in 1945, but the study wasn’t based on any research. Plus, most public health recommendations leave out the crucial second part of the guideline, which is that most of your water intake could come from food sources. Still, having a daily goal like eight glasses can help ensure that you’re drinking enough.
That being said, for healthy individuals, the only water drinking guideline you should seriously follow is your own. “The most important indicator is to drink when you feel thirsty. For most people, that’s the perfect solution,” says Charles Bourque, a professor at McGill University’s department of neurology who studies the neurophysiology of thirst. Thirst is a primordial emotion—it’s one of the instincts we’re genetically programmed for that help us stay alive. In fact, thirst originates in the same part of our brain, the anterior cingulate cortex, as other primordial emotions like hunger, pain and the need for air.
(Related: How Healthy Is Filtered Water?)
Why do I feel thirsty?
There are many factors that can stimulate the sensation of thirst. Heat is a big one: We mainly lose fluids through sweat, so when your body gets hot, it can trigger thirst, which tells your body that “you’re going to sweat, you’re going to lose water, you’re going to need to compensate for that later on,” Bourque explains. Sodium intake is another thirst trigger, as it increases your blood sodium concentration (more on that later). Anyone who’s ever had a super salty meal knows just how much water we can gulp down during it. “It’s not good to have rapid changes in sodium concentration, but you can dilute the sodium by drinking water, which is why it’s another very strong stimulus for thirst,” Bourque says.
We also lose water just by being alive. This is called obligatory fluid loss, and Cheung notes that even if you were bed-bound for a whole day in a comfortable temperature, “you would still end up losing about a litre of fluid a day, through the moisture on your skin,” he says. It does depend, though, on the size of your body, your metabolism and your environment: “If you were lying in the jungle, you’re going to be sweating a lot more and losing more sweat.”
While the parts of our brains that detect conditions like heat and sodium intake are different, they all activate the cingulate cortex. It’s also how we know not to drink too much water: Being overhydrated leads to a condition called hyponatremia (or water intoxication), which means low blood sodium. Luckily, for healthy people, if we drink too much, our bodies make us feel repulsed to water, so we stop drinking, Bourque explains. “There are sensors starting in your mouth that go through your throat and esophagus into your stomach,” he says. “All of these places have nerves that tell your brain, ‘Okay, enough fluid has been ingested,’ well before your body has fully recuperated.” As we age, our thirst signals diminish, so it’s important to stay aware of fluid intake and purposefully drink more water to compensate.
(Related: How to Boost Your Mood with Water)
What are electrolytes?
Our bodies also need to maintain a healthy level of electrolytes, which are minerals like sodium and potassium essential for nearly every bodily function, like regulating muscle contractions and balancing pH levels. We gain electrolytes naturally through a healthy diet and we lose them through sweating, urinating, defecating or vomiting. Does that then mean trendy electrolyte-filled waters like coconut water or Powerade are the way to go? The idea behind electrolyte drinks is to help retain fluid in your system. “Our bodies are a saline—there are salts in our plasma,” says Cheung. “So if you’re drinking pure water, it’s not going to be retained as well as if there were electrolytes in it. The whole point of electrolyte drinks is that our body absorbs water better when it’s closer to the electrolyte level in the body.” For most healthy individuals, though, unless you’re really active and sweating buckets, just drinking water and maintaining a healthy and varied diet is enough to stay hydrated.
Really, it depends on how salty your sweat is, Cheung says. The saltier the sweat, the more electrolytes are lost. The easiest way to determine the saltiness of your sweat is by looking at the stains left behind after a workout. “If you’ve gone for a run and your clothes are really crusted, it’s a good sign you’re a salty sweater,” says Cheung. “For those individuals, it’s important to increase the amount of electrolytes because you don’t want to lose too much while exercising.”
But again, we get electrolytes from the food we eat, so there’s really no reason to get them from fluids, unless you’re sick or sweating a lot. Plus, many sports drinks on the market have unhealthy additions like extra sugar. Even options that claim to have added vitamins, like Vitamin Water, don’t have enough to really make a difference, says Karenn Chan, an associate professor at the University of Alberta’s department of family medicine. “If you’re eating a reasonably healthy diet, you don’t need to supplement. There’s no evidence that drinking extra vitamins in your water makes you any healthier.”
(Related: Is It Bad to Drink Water That’s Been Sitting Overnight—Or Longer?)
What drinks dehydrate you?
Caffeinated drinks also get a bad rap for being dehydrating, but that’s a myth. Caffeine is a diuretic, meaning it increases your urine production. But it’s all about volume: Drip coffees contain a lot of water, which offsets the diuretics in your cup of joe. In order to get a negative diuretic effect, you’d pretty much need to be chugging tiny espressos (without added water!). Taking caffeine pills or chewing caffeine gum can cause you to become dehydrated, because you’re getting pure diuretic without any water content. But the same can’t be said for your regular cup of drip joe. “Coffee is also a rehydrating fluid, because we generally drink so much of it compared to the [diuretic] caffeine that we’re taking at the same time,” Cheung explains.
While everything should be consumed in moderation, any fluid intake is generally good. The only drink that isn’t hydrating is alcohol. A hormone called vasopressin tells our kidneys to reabsorb water—but it’s inhibited by ethanol. That means when you imbibe, your bladder fills up quickly, and if your kidneys aren’t reabsorbing water after you urinate, “you’d lose more water than the drink you’re ingesting and you could dehydrate yourself,” Bourque explains.
Chan says that many of her patients struggle with fluid intake, especially drinking water. So if someone is willing to get their daily fluids through coffee or tea, Chan says she’ll take it. “I say, ‘Do you like Jell-O? Or popsicles? Those things are mostly water.’ It’s about getting them fluids some other way,” she says.
“Just drink frequently and, if you want to, add a little bit of flavour to increase its palatability,” Cheung says. “You don’t need to overthink drinking water.”