You can eat well and exercise, but to round out your identity as a Person Who Makes Healthy Choices you may feel like you need to drain a large water bottle a few times a day. The benefits of chugging H2O are myriad and legendary, but are they real?

It seems every week somebody is proposing a new gadget or app to track how much water you drink (and prod you to drink more). Maxing out your water intake is a simple and actionable thing to do, but we know that focusing on small easy changes can backfire if they’re a distraction from the meaningful improvements you want to make in your life.

If tracking your water keeps you motivated for other changes, and you don’t feel like it’s sapping your willpower, keep on keepin’ on: a few extra glasses a day won’t hurt. But if you’re beating yourself up about missing your “water goal” every day, let’s take a look at when water does and doesn’t matter.

What Water Does

Here’s the worst argument for drinking more water: We are 75% water, or maybe 45%, or somewhere in between. (The exact number depends on body fat and other factors). Sure, water helps your blood flow, lubricates joints and other tissues, and is necessary for lots of the chemical reactions that keep us alive. When you zoom in to the molecular level, water is crucial for keeping our proteins and membranes in shape. We are water-based creatures. No doubt about that.


But that doesn’t mean more is always better. As one group of dermatologists wrote:

If this kind of logic were applied to gasoline and motor vehicles, the reasoning would be: because gasoline is essential for the car to function, we need to maintain large amounts of gasoline in our car’s tank, and the more the better.

Clearly, it’s bad to run out of gas. Losing a significant amount of your body’s water can lead to consequences ranging from headache and nausea to, in extreme cases, kidney failure and death. Losing a little bit can leave you with bad breath and dry skin. But are you dehydrated right now? Probably not.


There Is No Dehydration Epidemic

Most of us already get more than eight glasses a day (although, as we’ve discussed before, eight glasses is not a magic number.) You might not feel like you’re getting that much if you’re using a strict accounting that only includes water, but when it comes to hydration, your body doesn’t know the difference between water you drink and water you get elsewhere.

We get roughly half of our daily water intake as food: watermelon and soup are more than 90% water, as you may have guessed, but even a cheeseburger is 42%. We also get water from other drinks like soda and coffee, even if they have caffeine. (While caffeine can act as a diuretic, your body adapts to that effect over time.)


Meanwhile, you’ll recall that being thirsty on occasion is normal, and doesn’t mean that you’re dehydrated: thirst appears around a 2% loss in body water, but you’re not dehydrated in a medical sense until you’ve lost about 5%. (Likewise, as much fun as it is to match your pee to color charts, medium to dark yellow urine is still well within the normal range.)

What Water Is (and Isn’t) Good For

If you’re already at a normal hydration level, the myriad benefits of water start to fade away. It’s still a great choice of beverage, but in many cases the actual health effects don’t live up to the ballyhoo.


Weight Loss

There’s no evidence that chugging water all day long contributes to weight loss, but water can be strategic in at least one way: swapping it for calorie-containing beverages at meals. A review of the effects of water on weight loss, published in Nutrition Reviews, concluded that such a swap is “promising,” but that more research is needed to figure out whether it works well as a long-term strategy or if we end up compensating for the lost calories somewhere else in our day.

Does water make you feel more full? The research flip-flops on this question, with plenty of studies on both sides. The latest, published in Obesity, falls on the “yes” side. Drinking water before meals seemed to help weight loss in the short term: the water drinkers lost an average of about three pounds over three months. There was plenty of variation though, with some subjects even gaining weight, so this isn’t an ironclad conclusion.


Skin Health

If you pinch a dehydrated person’s skin, it won’t snap back into position right away. But does that mean that hydrating yourself extra will make your skin even more youthful and vigorous? That’s the logic behind claims that chugging water is great for skin, but a review published in Clinics in Dermatology couldn’t find any solid evidence for this idea. Drinking an extra two liters of water a day, in one study, resulted in skin changes that could be measured in the lab, but no noticeable improvement in skin roughness or wrinkles.

Brain Function

Does mild dehydration keep your brain from working at its best? The answer is a definite “yes, but”. Yes, dehydrating people changes their mood and makes them perform worse on tests, but the conclusive studies here dehydrated people by having them run on treadmills or sweat out body water in the heat, as the review in Nutrition Reviews points out. That means the effects could be due to exercise or mild heat illness, rather than dehydration. Giving water to thirsty test-takers had inconsistent results: sometimes their scores went up, sometimes down. And, again, there’s no evidence that if you’re already hydrated, that more water would improve anything.


Organ Function

Another common claim is that drinking water helps you “flush toxins” from your body, but we know by now that you don’t need to do anything special to detox yourself: we aren’t full of toxins and the few we encounter are taken care of just fine by our organs’ normal functioning.


But organ function is where we find our true winner: kidney and bladder stones are the only health condition that’s been clearly associated with low water intake over time. That conclusion comes from a (different) review in Nutrition Reviews that was looking specifically for long-term health effects of dehydration. If you are prone to kidney stones, you should absolutely be drinking more water. Lots more water. Chug it.

Athletic Performance

Here’s where we get into some serious controversy: there are two schools of thought on how much water you should drink during exercise, and both have good points.


First, the basics: you need more water if you’re exercising than if you’re just sitting around. Since you lose water from sweating, exercise intensity and the ambient temperature make a big difference (you’ll need more water running in the heat than taking a walk on a chilly day). But how much is enough, and how much is too much?

There’s a rule of thumb that being mildly dehydrated, as little as losing 2% of your body weight, can hurt your performance (making you run slower in a race, for example, or feel terrible during your workout), but a review of recent research in the British Journal of Sports Medicine found that in real world situations, athletes’ performance doesn’t suffer until they lose at least 4%. (That would be 6 pounds’ loss for a 150-pound person, or in other words, kind of a lot.) In fact, mild dehydration may help performance in some cases (and no, it doesn’t cause cramping).


Most of us would prefer to avoid dehydration just to be safe. The question then is whether that means we should drink as much water as possible, before and during and after exercise; or whether sipping when thirsty is enough.

Here’s the disagreement. The American College of Sports Medicine has put out guidelines recommending that you track and measure your fluid intake; they provide approximate numbers, and suggest monitoring your weight before and after exercise to figure out if you’re drinking enough. “Thirst alone is not the best indicator of...the body’s fluid needs,” they said in a statement.

That was in response to a competing set of guidelines from the Institute of Medicine, which clearly state: “The vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide.” Sports scientists in this camp are concerned that fear of dehydration has led too many people to over-hydrate, which can result in its own set of health problems (including potentially fatal complications).


The latest consensus statement on overhydration concludes that athletes should drink to thirst, except in extreme situations like a marathon on a hot day, when a little pre-emptive guzzling may be necessary.

Water Is Fine, but Don’t Waste Your Willpower

While it’s possible to drink too much water, that’s only likely if you’re downing liter upon liter (as some people do during exercise when they’ve been told to push fluids). For everyday purposes, it doesn’t hurt to drink a few extra glasses a day. Just don’t stress out about how much you’re drinking, don’t worry about tracking every drop of water intake, and don’t worry about dehydration unless you actually feel it.


Illustration by Sam Woolley.
