How Much Water Should You Drink When It’s Hot Outside?

Record-setting high temperatures are dangerous not only for the planet, but also for human health. Whether you’re situated in the middle of a heat wave or you’re just trying to survive a scorching day, you’ll need strategies to cool off and stay well.

One of the most crucial is to stay hydrated. But do eight eight-ounce glasses really cut it amid skyrocketing temps?

What you need on a normal day—and a scorcher

Most adults should drink somewhere between 68 and 100 ounces of water each day, says Dr. Ashley Karpinos, associate professor of medicine, pediatrics, and sports medicine at Vanderbilt University Medical Center. Another way to keep track of your water intake is to halve your weight in pounds—then drink that number of ounces each day, says Dr. Dana Cohen, an integrative medicine practitioner in New York City and co-author of Quench, a book about the science behind hydration.

But “in the heat, everyone needs more water,” Karpinos says. If you’re working, exercising, or are otherwise active in hot weather, a good rule of thumb is to drink eight ounces of water every 15 to 20 minutes during the physical parts of your day, Karpinos says.

Seems simple, right? Not so much. Hydration is complex. Not only do some people need more water than others, but sometimes, a glass of H20 isn’t even the best solution. The following tips from experts can help ensure you’re properly hydrated when it’s hot outside.

Monitor your bathroom breaks

The best way to keep track of how hydrated you are in hot weather isn’t through the total ounces of water you drink, but rather how often you’re urinating, Cohen says. “If you’re not getting up and going to the bathroom every two or three hours, you’re not well-hydrated,” she says. “That is truly the best way to do it—not looking at your urine color, not pinching your skin.” (The skin-pinch test is often used to assess skin turgor, or how elastic your skin is. If you’re dehydrated, your skin might not bounce back as quickly after a gentle pinch.)

Dr. Seth Feltheimer, a primary care physician and associate professor of medicine at Columbia University Vagelos College of Physicians and Surgeons, agrees. “It’s not [about] how much you’re drinking, it’s what your urine output is,” he says. “If you’re not urinating, you’re not drinking enough.”

Think beyond water

Water is typically the best thing you can drink when it’s hot outside, Karpinos says. But other beverages can also do an excellent job keeping you hydrated. She recommends drinking something with electrolytes after about an hour in the heat. Sports drinks like Gatorade will do the trick, but Cohen recommends coconut water, as it contains natural electrolytes.

Some research suggests a surprising drink might be hydrating as well: milk. One small 2016 study published in the American Journal of Clinical Nutrition gave people 13 beverages and tested their urine output over the next four hours. All of the beverages tested (including still and sparkling water, soda, diet soda, hot and iced tea, beer, orange juice, coffee, a sports drink, skim and full-fat milk, and an oral rehydration solution) had more or less the same hydrating effect except for three standouts: the oral rehydration solution, full-fat milk, and skim milk. Cow’s milk has sodium and electrolytes, which could potentially stave off dehydration.

Skip the Aperol spritz and iced coffee

Generally speaking, any fluid is good for hydration except for drinks with caffeine and alcohol since both are diuretics, says Lina Begdache, a registered dietitian and associate professor at Binghamton University’s Decker College of Nursing and Health Sciences. It’s also important to avoid alcohol in the heat because it can interfere with the body’s ability to regulate its core temperature, Feltheimer says.

Cohen notes that coffee is only problematic in excess. “Anything over four cups of coffee, and it starts to become a diuretic,” she says.

Add water-rich foods to your diet

Eating foods with a high water content is a great way to stay hydrated in the heat, Karpinos says. She recommends fruits and vegetables like watermelon, cantaloupe, berries, peppers, lettuce, and cucumbers. “You can also add mint leaves or fresh orange slices to flavor your water, which can make it easier to drink enough.”

Cohen also recommends smoothies, as well as chia seeds and flax seeds because of their high fiber content. “Chia seeds are sort of the star of the show,” she says. “They plump up to three times their amount with water, so they really hold onto that hydration well.”

Hydrate before you feel thirsty

One of the biggest mistakes people make is waiting until they feel thirsty to drink water, Karpinos says. This is because by the time you feel thirsty, you’ve already lost fluid and you’re on the way to dehydration.

Begdache adds that it’s also good to drink water before bed and first thing in the morning since you lose water while you sleep to respiration and sweating.

Pay special attention to children and the elderly

Since children are smaller than adults, their stores of water are also smaller and they’re more likely to get dehydrated in hot weather, Feltheimer says. The amount of water children need varies—toddlers need about 32 ounces a day, while pre-teens need about 60 ounces, Karpinos says. “Watch children closely for facial flushing, fussiness, or less urination, which can be signs of dehydration,” she says.

Elderly people are more likely to become dehydrated as well. This is because the body’s water content decreases with age. One 2023 study published in the International Journal of Clinical and Laboratory Medicine looked at hydration status in nearly 1,000 elderly adults. Researchers found that 31% of participants were dehydrated. Diabetes and chronic renal failure were more common in the dehydrated group, as was their likelihood of experiencing a fall.

Athletes should exercise extra caution

It’s particularly important for athletes to have a hydration plan in the heat, says Karpinos, who is the team physician for Vanderbilt University athletics. “The goal is to start an exercise session well-hydrated, maintain hydration during exercise, and then correct excessive losses afterward,” she says.

The amount of water to add will vary depending on the athlete’s sex, weight, and how much they sweat, as well as the intensity of the workout and the temperature outside, she says. But in general, athletes should drink an additional 12 ounces of water two hours before exercise and about eight ounces of water every 15 to 20 minutes during the workout, Karpinos says.

Athletes should also check for signs of dehydration when they’re done exercising. “If athletes lose weight quickly during an exercise session, that can be a sign of dehydration,” Karpinos says. “In this case, we recommend drinking about 20 ounces of fluids for every one pound lost during the exercise session to correct the dehydration.”

Be on the lookout for dehydration

Early signs of dehydration include feeling thirsty, having dry lips and mouth, not sweating enough, and dark urine, Karpinos says. Feltheimer adds that body cramps, lethargy, and an inability to urinate “are all signs that your body is trying to conserve whatever fluid it has.”

Being dehydrated can have a greater impact than many people realize. Even just a 2% drop in hydration can lead to brain fog, headaches, and dizziness, Cohen says. One 2019 study found dehydration can also have a negative effect on short-term memory, attention, energy, and mood.

Read More: How to Cool Your Body Down Fast

Drinking enough water is also important long-term. One 2023 study published in the Lancet found chronic dehydration can lead to premature aging, chronic disease (including heart failure, diabetes, and dementia), and premature death.

“There’s nothing that can function in the body without hydration, down to the cellular level,” Cohen says. “The single most important thing we can do to treat and prevent chronic disease is learn how to hydrate properly.”

Don’t overhydrate

Some people—in an attempt to stay hydrated on hot summer days—overdo it. Cohen says she regularly sees patients with lab results that are too low in sodium and chloride because they’re drinking too much water. “I see this more often than [you’d] think,” she says. Overhydration, she says, can lead to many of the same symptoms as dehydration, like muscle cramps and fatigue.

Although a little extra water is nothing to worry about, drinking way too much can lead to hyponatremia, a condition caused by not enough sodium in the blood that can lead to seizures. Cohen notes that overhydrating to this level is exceptionally rare, but it’s still something to be aware of.

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