A tired athlete rubbing sweat off her forehead with her sweatband and drinking from a yellow water bottle. Learn how to rehydrate in this article.

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How to Rehydrate Safely and Quickly, According to Dietitians

Refill your tank with these expert-backed hydration strategies.

By Karla WalshApril 12, 2024

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To put it (very) simply, drinking enough water is crucial. 

“The body can’t function properly without water,” says Roxana Ehsani, RD, a Miami-based board-certified sports dietitian. “No other nutrient is needed in a great amount on a daily basis.” 

So when we don’t drink enough liquids and end up dehydrated, we hamper our ability to regulate blood pressure and volume, protect and lubricate joints, manage body temperature, transport nutrients and oxygen from head to toe, and transform food into energy our bodies can use during our next workout.

Sounds pretty important, right? It is, yet many of us—especially athletes who lose a fair amount of water in their sweat—struggle with how to rehydrate properly throughout the day. What, exactly, should you do when you need to refill your water tank?

To coach you through everything you need to know about how to rehydrate, we asked three experts to spill their H2O guidance: Ehsani; Kelly Jones, RD, a Newton, Pennsylvania-based board-certified sports dietitian; and Mary Stewart, RD, a registered dietitian and the founder of Cultivate Nutrition in Dallas.

Common Signs of Dehydration

Before we dive into when, why, and how to rehydrate, let’s brush up on what it feels like to be dehydrated so you can be aware of the symptoms before things get too severe.

The most common signs of dehydration vary from person to person, but may include any or all of the following symptoms, according to the three experts we spoke with:

  • Increased physical fatigue or perceived effort during a typical workout

  • Difficulty concentrating

  • Poor or slow digestion, constipation, and/or bloating

  • Dry or cracked lips

  • Decreased sleep quality

  • Slower recovery post-workout

Even mild dehydration can impact your health—and definitely not for the better. And at greater fluid losses of 4 percent or more of total body weight, “we get into levels of dehydration more concerning from a medical perspective,” Jones says. At this point, dehydration is not just detracting from optimal physical and mental performance; it can also lead to increased heart rate, a spike in respiratory rate, dizziness, flushed skin, irritability, and/or emotional instability, she adds.

As funny as it may sound, your urine can clue you into your hydration status. Take note of:

  • Color. “Your urine color should be light like lemonade, not dark like apple juice,” Ehsani says. “If it’s dark in color, it could be a sign that you are dehydrated.” 

  • Volume. Urinating a very small amount each time you try to go could be another sign you’re dehydrated.

  • Visits. “Most people should be urinating every two to four hours,” Ehsani says. “If it has been more than that since your last visit to the restroom, you may be dehydrated.” 

When Might You Need to Hydrate More Than Usual?

You might think you only need to worry about upping your fluid intake before, during, and after a workout. While it’s important to stay plenty hydrated for exercise, Jones says other situations may call for increasing your H2O intake, too.

“When our body is put in a situation that loses fluid, our demand for more water to stay properly hydrated goes up,” Stewart explains. “If water loss surpasses water replacement, we become dehydrated.”

According to the dietitians we spoke with, the following scenarios may benefit from rehydrating during and after:

  • Sweating due to a workout or excessive heat

  • Moving more throughout the day, even when it’s not officially “exercise” (looking at you, all-day spring cleaning!)

  • Spending time in an arid climate

  • Traveling, particularly if there are significant altitude changes or swift environmental shifts involved

  • Taking certain medications, including diuretics

  • Suffering from an illness, especially one that involves vomiting or diarrhea

“In terms of illness, it’s critical to monitor fluid, electrolyte, and carbohydrate intake with gastrointestinal illness that causes vomiting or diarrhea due to obvious fluid losses,” Jones explains. “However, keeping fluid intake up with everything from fever to head colds is also important to support a healthy immune system and prevent body temperature from rising to more dangerous levels.”

A man carrying a yoga mat under his arm and drinking from a water bottle with the other. Learn how to rehydrate in this article.

Kobus Louw / E+ via Getty Images

How to Rehydrate Safely

“The exact formula to rehydrate once dehydrated is going to vary based on an individual’s needs and severity of dehydration,” Stewart says.

However, no matter your health history, body size, or cause for feeling parched, if you notice any of the aforementioned dehydration symptoms, Ehsani says it’s a wise idea to sip on 8–16 ounces of water, just in case. 

Your Body Weight Can Signal How Much Water You Need

Your body weight can clue you in on how to rehydrate, experts say. If possible (and only if you feel comfortable doing so), weigh yourself before your workout, or before taking a trip, knocking out some sweaty outdoor yard work, or undergoing a similar situation. Then weigh yourself after completing the activity to see if you’ve kept up with your H2O needs or have some ground to make up, Stewart says.

“Individuals needing quick and complete recovery from excessive dehydration can drink about 1½ liters of fluid for each kilogram of body weight lost. This comes out to be about 25 ounces per pound lost,” she says.

For an easy-to-remember rule of thumb, Ehsani tells her clients to replace one pound of weight loss with 24 ounces of fluid. So if you’ve lost four pounds after a two-hour bike ride, for instance, you’d need to technically replace what you’ve lost, which nets out to be about 96 fluid ounces. “You don’t have to try to drink this all within the next hour, as that’s a lot of fluid to rehydrate with, but it’s a good idea to try to hit that number within the next 24 hours post-workout (or try to do it before you hit the bike again or exercise in another way),” Ehsani says.

Should You Rehydrate with Electrolytes and Carbs, Too?

If your dehydration is related to an increase in sweating or the result of an illness that triggered a drastic loss of fluids, it’s best to not only replace the lost fluids but also add electrolytes, according to the dietitians we spoke with. Electrolytes are important minerals (such as potassium, sodium, and magnesium) the body needs to properly rehydrate. (They also play an important role in muscle function, heart health, and healthy blood pressure.) 

Beyond water and electrolytes, the rehydration process should also involve carbohydrates, Jones says. “Increased activity, illness, altitude, and adaptation to other environmental changes all cause increases in energy and carbohydrate metabolism,” she explains. “This matters for fluid balance because each gram of carbohydrate we store in the muscles as glycogen holds on to almost 3 milliliters of fluid. This is why many people experience several pounds of weight loss when sick or in warm environments.”

Carbohydrates and one electrolyte in particular, sodium, help increase the absorption of one another—and of fluid, Jones continues. Think of it like the cardio, strength training, and stretching aspects of your fitness routine: All are important and beneficial on their own, but they’re far more effective and better together. 

How to Rehydrate for Minor Dehydration

If you’re slightly dehydrated from a typical workout that was less than one hour long, or if you performed increased amounts of light to moderate activity throughout the day, a slight increase in fluids and electrolytes paired with normal meals that contain nutrient-rich carbohydrate foods should be adequate, Jones confirms.

Keep in mind that you can get electrolytes and fluids from food sources, Ehsani adds. Carbs almost always come naturally “packaged” with food, too. If you’d prefer to eat your water, electrolytes, and carbs rather than drink them, soup checks all the boxes. Crackers and pretzels are among Ehsani’s top sodium- and carb-strong snacks, which would pair well with plain water. “Fruits and veggies are 80–99 percent water, so they are an excellent choice to aid in hydration,” Stewart adds.

How to Rehydrate for Moderate or Severe Dehydration

If you’re experiencing higher levels of fluid loss, aim to stay in a cool environment as much as possible, relax (rather than engaging in more activity), and sip on a sports drink or electrolyte beverage. 

For severe dehydration (which, for what it’s worth, typically wouldn’t happen after a standard workout), the World Health Organization recommends an Oral Rehydration Salts (ORS) solution that delivers a mix of water, sodium, and carbohydrates. To make your own, Jones suggests combining 16 ounces of water, 3 teaspoons of sugar, and ¼ teaspoon of salt.

With both moderate and severe dehydration, treatment may require an IV to rehydrate your body directly through a vein. This can be performed at an urgent care clinic, hospital, or emergency room, depending on the severity, the Cleveland Clinic confirms. And if you’re dealing with a gastrointestinal illness or have a high fever for more than 48 hours, it’s best to seek medical attention, Jones advises. 

How Long Does It Take to Rehydrate?

The length of time to return to an optimally hydrated state will depend on a few different factors, Jones says, including:

  • The severity of fluid and electrolyte loss

  • The ability to get adequate sodium and carbohydrates with the fluids you drink

  • Whether or not you’re still in a state or environment that’s promoting dehydration (such as being in a significantly high or low altitude or a hot or cool environment, or still feeling sick rather than on the mend)

“Water is processed in the digestive tract, and gets mostly absorbed in the bloodstream by the small intestine,” Stewart says. “The good news is that water can be absorbed in as quickly as five minutes, kick-starting your rehydration process.”

Other hydrating liquids, such as electrolyte and carbohydrate drinks, juices, or smoothies, will take longer (about 20–60 minutes, depending on the beverage, per the Cleveland Clinic) for full absorption. 

Rehydration time will vary from person to person, so keep an eye on your urine: What color is it? Have you had to urinate every two to four hours yet? How much are you urinating each time? This is your best guide to determine if you’re back to a well-hydrated state.

Tips for Preventing Dehydration

The US National Academies of Sciences, Engineering, and Medicine suggests men consume 3.7 liters of water per day (15½ cups) and women consume 2.7 liters per day (11½ cups), which can come from fluids or food.

“That’s the daily goal, but this may increase if you’re physically active or need additional fluid due to the conditions mentioned above,” Ehsani reminds us.

To reduce the risk of dehydration—and of needing to worry about how to rehydrate fast—the dietitians we spoke with recommend following these prevention tips:

  • Start your day with water. Yes, coffee and tea “count,” but regular water is even better.

  • Carry a reusable water bottle and sip from it often.

  • Enjoy fluids at your preferred temperature. If you prefer ice, keep your freezer well-stocked. Or if room temp is your jam, keep a filtered pitcher full of water within arm’s reach.

  • Customize your cup. If you crave flavor, try adding citrus slices, berries, or herbs. If bubbles are enticing, stock up on sparkling water or invest in a machine that allows you to make your own.

  • Set an alarm each hour during the workday to remind you to drink at least 8 ounces of water if you tend to forget.

“Keep in mind you don’t need to overdo it,” Ehsani says. “There’s a risk of hyponatremia, or fluid overload too if you rapidly decide to start chugging glass after glass of water, which can be dangerous too.” (Everything in moderation, even hydration.)

The Takeaway

Rehydration may be necessary if you’ve lost a substantial amount of fluid due to sweat-inducing physical activity, environmental conditions, or illness. Your urine and body weight can help clue you in about your hydration status, as can dehydration symptoms like fatigue, headache, digestive distress, and difficulty focusing.

To rehydrate safely, focus on prioritizing water, electrolytes, and carbohydrates, which work in tandem to aid in restoring the body’s fluid balance.

Ideally, you’d be refilling your internal water tank early and often, not just when you’re feeling incredibly thirsty or are in the middle of a challenging running or cycling class.

“Staying hydrated should be part of your daily lifestyle, and not something you only think about when you exercise,” Stewart says. “One of the best things we can do is to get enough to drink before, during and after activity. Try to be consistent with it throughout the day so you don’t have to make a concerted effort to rush and rehydrate.”

This content is for informational and educational purposes only and does not constitute individualized advice. It is not intended to replace professional medical evaluation, diagnosis, or treatment. Seek the advice of your physician for questions you may have regarding your health or a medical condition. If you are having a medical emergency, call your physician or 911 immediately.

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