Drinking a Gallon of Water a Day: Benefits and Risks, Explained

If you’ve been lugging around one of those popular gallon-sized water bottles and trying to swig your way down to the bottom by the end of the day, here’s a message for you: It’s really, really great that you’re focusing on hydration, because it’s important for your health. But also know this: You really, really don’t need to drink a gallon of water a day.

“Just like caloric intake and energy expenditure, there is no magical ‘one size fits all’ when it comes to the daily water requirements that everyone needs to ‘stay healthy,’” says Tamara Hew-Butler, D.P.M., Ph.D., F.A.C.S.M., associate professor, exercise and sport science at the College of Education, Wayne State University. “Although ‘Gallon Challenges’ and ‘8 x 8’ glasses per day recommendations are widely touted by both lay people and health professionals alike, the science behind these recommendations is largely mythical but widely propagated through clever marketing — think bottled water, oxygenated water, vitamin water, alkaline water, etc. — rather than clinical evidence.”

Why can drinking a gallon of water per day be too much? Keep in mind that your body doesn’t just get water from drinking water. In fact, it’s been estimated that Americans get as much as 22% of their water intake from foods — including beverages like milk and juice, fruits and veggies, and even packaged foods like yogurt and pasta.

“Our bodies contain roughly 60% water,” adds Kelly Anne Hyndman, Ph.D., assistant professor of cardio-renal physiology and medicine (Division Nephrology) at the University of Alabama at Birmingham, who researches kidney function. “The body wants to remain in balance, which means whatever water or salt we lose through our sweat, respiration, and urine and feces has to be replaced daily. And our bodies are very good at maintaining our body fluids and salts at specific concentrations, because that’s what is best for all of our organs to function properly.”

“Each person has a different water need,” continues Hyndman. “Age, sex, body mass index, activity level, diet, climate and other factors all contribute to how much water we may actually require. This is why a gallon a day is not appropriate for everyone. Of course, there are times when we aren’t in balance, but one job of our kidneys is to regulate how much salt and water we keep and how much gets excreted in our urine. In doing so, our kidneys help us return to a balanced state.”

But can drinking too much water — or too little — be dangerous?

“When we drink more than what we need — or don’t drink as much as we need — in healthy individuals, it puts a little stress on our kidneys, but our kidneys are very good at trying to help us return to balance, so generally it will be ok,” says Hyndman. However, she adds, if a person has underlying diseases, drinking too much or not enough can really cause issues.

Here’s why it could cause negative effects for those people, according to Hyndman:

“When we drink excess water, it’s absorbed by our gastrointestinal tract and enters our plasma, the fluid part of our blood. Our plasma has very specific concentrations of proteins, salts, hormones, etc. Our kidneys filter our plasma to help remove excess waste products from metabolism, and excess water and salts. But our kidneys can only filter so fast, and there can come a point when they can’t filter the water out fast enough — and this will cause our plasma to be too dilute and affect our plasma salt concentration. If you have a disease like chronic kidney disease or congestive heart failure, drinking too much water may lead to very low plasma sodium levels. That can lead to all sorts of problems, which may manifest as headaches, seizures, brain swelling and in some cases, death.”

There’s also a risk for certain people if they aren’t hydrating enough, though, she adds: “On the other side, if you experience kidney stones, drinking too little water can cause kidney stone formation and lead to kidney damage. So for these individuals, generally they should drink more water to help prevent this.”

How hydration helps (and doesn’t)

Ok, so you don’t need to drink a gallon a day — and we know that many of you out there are thinking, Whew! Fewer bathroom runs! But hydration has an impact on your body, of course, so here’s what you need to know about its impact in various situations.

When you’re working out

“If you’re performing high intensity exercise, particularly in the heat, you should always have fluids freely available, to replace sweat water and salt losses when you get thirsty,” says Hew-Butler. “Your body produces sweat to cool your body down. When the body runs low on fluids, your brain and the sensors within your heart can detect low water/high salt concentrations and trigger the sensation of thirst. Thirst is the body’s most accurate real-time biological monitor of body water levels, while the kidneys react directly to signals from the brain to either retain body water or get rid of excess fluids. When you get thirsty, it is not ‘too late’ to hydrate, as the balance between water and salt is tightly regulated by the brain and kidney so that all animals can survive in a variety of environments.”

For metabolism and weight loss

“Water can help with weight loss,” says Hyndman, “but studies show that’s generally because the individual who lost weight exchanged drinking high calorie drinks, like juices and soda, for water.” One study showed that replacing diet beverages with water led to weight loss, she adds. “The researchers also report this beverage replacement may improve carbohydrate metabolism and improve insulin resistance. The important thing here is that these women were on a six-month weight loss plan, so it appears that switching from diet beverages to water had an additional beneficial behavior even 12 months after the weight plan. In other words, it may not be a direct effect of water per se but rather a choice to live a healthier life style.” Water may also help you feel a bit fuller when you eat, she says — but you certainly don’t need to drink a gallon a day.

For brain function

Research has shown that taking in enough — or not enough — water has an impact on how sharp you function and feel. The studies indicate that short-term memory, concentration, math abilities and psychomotor skills are affected by dehydration, as well as the brain’s ability to understand information in complex or confusing situations. Even mild dehydration can sometimes have an effect on your mood (cranky alert!) and cognitive functioning, though these findings haven’t been consistent. In one study, the participants reported that water intake increased their alertness.

Taking in too much water can affect our brain as well, says Hyndman. “Our brain is very sensitive to changes in body salts and water, like all the other cells in our body,” she says. “When we drink so much water that our kidneys can’t effectively excrete it fast enough, then our plasma becomes dilute (low plasma sodium) and that will cause water to move into our cells and swell them. In the brain this is especially dangerous because our skull leaves little room for our brain to swell. Also, this changes our salt concentration in the body, and that causes neurological issues— again our body wants to maintain specific salt and water concentrations so that our organs function properly.” Hyndman stresses that in healthy individuals, this scenario is very rare. “Our kidneys are that good at preventing these changes.”

For headaches

You may have heard the advice that at the first sign of a headache, you should drink a big glass of water — and there’s some science to back that up. Observational studies have shown that water deprivation can be a trigger for migraine. Other research has shown that swigging water brought headache relief to participants within a half-hour to three hours. As to whether drinking water regularly can prevent headaches: There really isn’t research to back that up, but it also hasn’t been disproven.

For younger-looking skin

Hate to debunk this myth: Despite what you’ve read, drinking water will not prevent wrinkles or signs of aging, according to research. And there’s no scientific evidence that it will flush toxins from your skin or give you a look that glows. Here’s what drinking enough water can do, especially if you haven’t been getting enough: It could possibly improve your skin’s thickness and offset the amount of water you lose via your skin, thus improving skin dullness.

Says Hyndman, “Our skin contains lots of water and it helps our skin maintain elasticity. When you pinch the skin on the back of your hand, if you are properly hydrated it will bounce back. But if you are severely dehydrated the pinch will stay. But will drinking more water improve skin hydration and elasticity? Although it seems logical, I think more studies are needed.” As to the belief that drinking H2O can detoxify your skin, Hyndman says, “Water can only help remove water-soluble molecules that are excreted by the kidneys, say like vitamin C. I’m not sure what ‘toxins’ people think water is removing.”

If your skin is dry, it’s usually because you’ve been hanging out where the air is arid, taking too-hot showers, or scrubbing too hard with soap. It also could be due to a medical condition or medications. And aging and wrinkles are usually due to sun and other environmental damage, not to mention basic genetics. So sure, drink up — but also wear sunblock, lower the water temp when you shower and be gentle when you wash your face.

Do you need to drink more water?

So, key question: How do you know if you need to hydrate more?

Here’s Hyndman’s advice: “For healthy young adults, drinking when you’re thirsty is the way to go.” For children and older individuals, she says, the guidance is harder, “because generally by the time they’re thirsty, it can be more problematic. As we age, our ability to sense our body water status starts to decline. For older individuals, if you know you’re going to be exercising, working in the garden or being active, then consider drinking a little bit before, during and after. Consuming small volumes throughout the day will help you remain in water balance.”

So how can you tell if you’re getting enough, or too much, water? “If your pee is very faint in color and you are urinating every hour, or so frequently it interrupts your quality of life, then you are likely consuming too much fluid,” says Hyndman. She suggests trying the skin-pinch test, mentioned above: “Pinch your skin on the back of your hand, and if it doesn’t bounce back, you probably need to drink more water. But generally, if you are consuming so much water and other beverages that you’re urinating so frequently that it’s affecting your quality of life, then you should try drinking less and see how you feel.”

When it comes to drinking water, here’s Hew-Butler’s bottom line guidance:

“Whether you are an elite athlete performing high intensity exercise or a weekend warrior engaging in leisurely activities like gardening or walking, proper hydration advice is the same: Listen to your brain and drink when you feel thirsty—any beverage that’s appealing at the time! If you overshoot the water intake, your kidneys will promptly excrete the excess fluids, and if you undershoot water intake, your thirst will dominate all other sensations until you find fluids. The sensors located within your brain, and rapid communication between your brain and kidney, will tell you precisely how much fluid you need in real time. So drink up – when you are thirsty. It truly is that simple.”

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