What you need to do to stay hydrated

According to Ashley Karpinos, associate professor of medicine, pediatrics, and sports medicine at Vanderbilt University Medical Center, most adults should be drinking between 68 and 100 ounces of water each day.

Another way to keep track of your water intake is to divide your weight in pounds in half and drink that number of ounces each day, according to Dana Cohen, an integrative medicine practitioner in New York.

However, "in the heat, everyone needs more water," Karpinos said. If you're active in hot weather, Karpinos recommends drinking eight ounces of water every 15 to 20 minutes during the physical parts of your day.

Water recommendations can vary by person. Children, for example, have smaller stores of water given their smaller bodies and are more likely to get dehydrated in hot weather, according to Seth Feltheimer, a primary care physician and associate professor of medicine at Columbia University Vagelos College of Physicians and Surgeons.

The amount of water children should have varies — toddlers should have around 32 ounces a day while preteens should have around 60 ounces, Karpinos said. "Watch children closely for facial flushing, fussiness, or less urination, which can be signs of dehydration," she added.

Elderly people are also more likely to become dehydrated, as the body's water content decreases with age. One study from 2023 published in the International Journal of Clinical and Laboratory Medicine looked at the hydration status of almost 1,000 elderly adults and found that 31% were dehydrated.

Athletes should also pay close attention to hydration in the heat, Karpinos said. "The goal is to start an exercise session well-hydrated, maintain hydration during exercise, and then correct excessive losses afterward," she said.

Water intake recommendations for athletes vary depending on the person's sex, weight, and how much they sweat, as well as how intense their workout is and how hot it is outside, Karpinos said. But generally speaking, athletes should drink an additional 12 ounces of water two hours before exercise and around eight ounces every 15 to 20 minutes during. The American College of Sports Medicine also recommends people add 12 ounces of water each day for every 30 minutes of exercise.

Water isn't the only thing that can hydrate you

According to Karpinos, while water is typically the best thing to drink when it's hot outside, there are other beverages that can also keep you hydrated.

Karpinos recommends drinking something with electrolytes after around an hour in the heat. Sports drinks like Gatorade can also help, but Cohen recommends coconut water, as it contains natural electrolytes.

Other research has suggested that milk could be a hydrating drink as well. One study from 2016 published in the American Journal of Clinical Nutrition gave people 13 beverages and tested their urine output over the course of the next four hours.

The researchers tested 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. All of the tested beverages had roughly the same hydrating effect except for the oral rehydration solution, full-fat milk, and skim milk, which had higher beverage hydration indexes than the still water control. Cow's milk contains sodium and electrolytes, which could help prevent dehydration.

According to Lina Begdache, a registered dietitian and associate professor at Binghamton University's Decker College of Nursing and Health Sciences, any fluid is generally good for hydration except for any drinks with caffeine or alcohol, since both are diuretics.

Feltheimer added that it's important to avoid alcohol in the heat because it can interfere with the body's ability to regulate its core temperature.

Meanwhile, coffee is only a problem in excess, Cohen said. "Anything over four cups of coffee, and it starts to become a diuretic."

Foods with a high water content can also help you stay hydrated, Karpinos said. 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 recommends smoothies, as well as chia seeds and flax seeds since they have high amounts of fiber. "Chia seeds are sort of the star of the show," Cohen said. "They plump up to three times their amount with water, so they really hold onto that hydration well."

How to tell if you're dehydrated

According to Karpinos, early signs of dehydration can include feeling thirsty, having dry lips and mouth, not sweating enough, and dark urine. Feltheimer added that body cramps, lethargy, and an inability to urinate "are all signs that your body is trying to conserve whatever fluid it has."

Paying attention to urination is the best way to keep track of how hydrated you are in hot weather, according to Cohen. "If you're not getting up and going to the bathroom every two or three hours, you're not well-hydrated," she said. "That is truly the best way to do it."

"It's not [about] how much you're drinking, it's what your urine output is," Feltheimer said. "If you're not urinating, you're not drinking enough."

It's also important to drink before you feel thirsty. According to Karpinos, once you feel thirsty, you've already lost fluid and are on the path towards dehydration.

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

Athletes should also pay close attention to 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 said. "In this case, we recommend drinking about 20 ounces of fluids for every one pound lost during the exercise session to correct the dehydration."

Being dehydrated can have a significant impact on the body. According to Cohen, just a 2% drop in hydration can lead to brain fog, headaches, and dizziness. One study from 2019 found that dehydration can also have a negative effect on short-term memory, attention, energy, and mood.

However, while it's important to stay hydrated, experts caution against overdoing it. Cohen said she regularly sees patients whose lab results show they're too low in sodium and chloride because they're drinking too much water. "I see this more often than [you'd] think," she said.

According to Cohen, overhydration can lead to many of the same symptoms as dehydration, including muscle cramps and fatigue. While a little extra water isn't something to worry about, overhydrating can eventually lead to hyponatremia, a condition caused by a lack of sodium in the blood that can lead to seizures. Cohen noted that overhydrating to that extreme is rare, but something to be aware of. (Serrano, TIME, 7/8; Lee, Forbes, 7/15)

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