How to rehydrate fast: What the science says

Written by Jennifer Chesak (opens in a new tab)

Medically reviewed by Ecler Ercole Jaqua, MD, MBA, DABOM (opens in a new tab) and Jared Meacham PhD., RD, CSCS (opens in a new tab)

Dehydration means your body has lost fluid in an amount that affects its functioning. People typically lose electrolytes with fluid loss, as well. Rehydrating fast involves consuming enough fluid and adequate amounts of electrolytes to support fluid balance and bodily processes, such as nerve and muscle function. How long it’ll take you to get rehydrated depends on individual factors, including how much fluid you’ve lost and why.

Fun fact: Your body is made up of 50% to 60%Opens in a new tab water. Additional fun facts: Your lungs are made up of about 83% water, your kidneys and muscles about 79% each, your brain and heart about 73% each, your skin about 64%, and your bones about 31%.

Now you can slay at your next trivia night, but do you know how to rehydrate fast or what to drink when dehydrated?

DehydrationOpens in a new tab occurs when the body loses too much water and other fluids to perform its functions properly. As you can see by how much of our bodies is actually water, a major reduction in fluid impacts nearly every bodily system, and if dehydration happens to you, you’ll need to rehydrate fast — with fluid and electrolytes.

I’ve been there. My migraine attacks typically come with a side of nausea and vomiting. Not to get all TMI on you, but a few years ago I had an attack that left me vomiting until I was dry heaving. I couldn’t keep anything down for over eight hours and was miserable.

I hauled my dehydrated self to urgent care, where a litany of healthcare providers tried to give me intravenous (IV) fluids. I say “tried” because my blood volume had substantially decreased, making IV insertion difficult. So they switched the focus to resolving my upset stomach with an anti-nausea medication I placed under my tongue.

Eventually, I was able to keep fluids down, and eventually I felt better. I say “eventually” because the situation took a while. Drinking fluids and electrolytes doesn’t rehydrate you immediately.

“Restoring fluid and electrolyte balance isn’t instantaneous,” says Michael Israetel, PhDOpens in a new tab, chief content officer and cofounder of Renaissance Periodization. “It’s slower and more complex than most assume. Fluid needs to be absorbed from the gut, distributed through the bloodstream, and finally reach the muscles and other tissues. This process often takes 45 minutes to two hours or even longer, depending on dehydration severity. The sooner you initiate rehydration, the quicker you’ll regain optimal physical and cognitive performance.”

"Rehydration Checklist Drink one glass of water with one electrolyte packet every 30 minutes. Add a pinch of salt to water if no electrolyte mix is available. Avoid plain water alone in the first one to two hours of rehydrating. Watch for symptom improvement within one to two hours, and seek help if your symptoms are not improving."

But what is dehydration exactly? Is it all about water loss? How about those electrolytes? And what is the fastest way to rehydrate? In this article, we tackle these questions and more.

Understanding Dehydration

Dehydration means you’ve lost too much fluid. But with water loss through sweat, urination, diarrhea, or my aforementioned vomiting, we also lose crucial electrolytesOpens in a new tab, which help maintain fluid balance and support bodily processes, such as nerve signaling and muscle function.

Complicating matters is that dehydration can also cause an overconcentration in the blood of certain electrolytes. This is because when dehydration occurs, we typically lose water more rapidly than we lose electrolytes. Additionally, we can become overhydrated by drinking too much plain water, which can then dilute electrolytes in the body.

Here’s a breakdown of the terminology:

Dehydrated: The body has lost too much fluid.
Overhydrated: The body has too much water.
Electrolyte imbalanceOpens in a new tab: The body has either an overconcentration or dilution of electrolytes, including sodium, potassium, chloride, magnesium, calcium, phosphate, and bicarbonate.

Both dehydration and overhydration can cause an electrolyte imbalance, and the medical community has specific namesOpens in a new tab for these issues.

Types of dehydration:

Isotonic: Water and sodium have been lost equally, often because of vomiting or diarrhea.
Hypertonic: Water loss has exceeded sodium loss (a condition called hypernatremia), often because of sweating, inadequate fluid intake, or underlying conditions.
Hypotonic: Sodium loss has exceeded water loss (a condition called hyponatremia), often because of underlying conditions or consuming too much plain water.

Special considerations regarding hydration

Some adults and children may have different needs regarding staying hydrated and should consult their healthcare providers.

Older adults may have blunted thirst sensationsOpens in a new tab, potentially placing them more at risk for hyponatremia.
Children, when dehydrated, may require the World Health Organization (WHO)-recommended oral rehydration solution (ORS).
People with kidney disease or congestive heart failure may require fluid or electrolyte restrictions and should follow their doctor’s recommendations for staying hydrated.

Common signs and symptoms of dehydration

Although symptoms vary, here are some common signsOpens in a new tab you’re experiencing dehydration:

Dry mouth or throat
Dry skin
Fatigue
Headache
Less frequent urination
Muscle crampsOpens in a new tab
Nausea
Substantial drops in physical or cognitive performance
Thirst
Weakness

If you experience rapid heartbeat (tachycardia), confusion, fainting, hallucinations, high fever, loss of consciousness, seizures, hypotension (low blood pressure), unusually dark urine, or lack of sweating even when hot, you should seek immediate medical attention.

“If patients are hypotensive and tachycardic, intravenous fluids are given relatively quickly in the ER, usually over 30 to 60 mins,” says Paul Nystrom, MDOpens in a new tab, an emergency medical physician who served as a Dive Medical Officer assigned to Navy SEAL teams. “If they can tolerate oral rehydration, that is also an option and in the ER that looks like water, juice, and often saltine crackers.”

Fastest Way To Rehydrate

If you are not experiencing a medical emergency, the fastest way to rehydrate at home or elsewhere is by drinking fluids containing electrolytesOpens in a new tab. Specifically, sodium, chloride, potassium, and magnesium are crucial.

Sodium helps maintain fluid balance, supports nerve and muscle function, aids nutrient transport across cell membranes, and regulates blood pressure.
Chloride aids with digestion, helps maintain fluid and pH balance, plays a role in nerve and muscle function, and facilitates the transport of oxygen into cells and carbon dioxide out of cells.
Potassium works alongside sodium to maintain fluid balance via a mechanism called the sodium-potassium pump (see more on this below). PotassiumOpens in a new tab also staves off muscle weakness and cramps and supports cardiovascular health.
Magnesium is crucial for proper muscle and nerve function, neurotransmitter release, and helping your cells convert food into energy.

How much of each electrolyte do you need? And how do you get enough and in the right ratios? We can look to research to gauge how much electrolytes are typically lost through sweat. Sodium loss exceeds potassium. Some research suggests that you lose about 500 milligrams of sodiumOpens in a new tab and 120 mg of potassiumOpens in a new tab per hour, depending on activity intensity, environment, and individual variability. For magnesium, the range is about 10 to 20 milligramsOpens in a new tab per liter of sweat loss. But if you’re engaging in intense physical activity, regardless of the weather, you will likely lose even more electrolytes than these estimates. Complicating matters is that some dietary choices can amp up your sodium needs.

If you consume a low-carb Opens in a new tabdiet, eat mostly whole foods, or do any type of fasting, you can lose even more sodium through urineOpens in a new tab and will have higher sodium-intake needs.

"“Drinking plain water without electrolyte replenishment carries risks such as failure to replace critical electrolytes (particularly sodium, potassium, magnesium, and chloride), and active dilution and flushing of electrolytes through excessive plain water intake.” Michael Israetel, PhD, Sport Physiology "

One more consideration: Our bodies have this fancy built-in sodium-potassium pumpOpens in a new tab. It’s really a protein in our cell membranes that has a crucial function. With the help of energy created from adenosine triphosphate (ATP), the body’s universal form of energy, the pump hands over three sodium ions in exchange for two potassium ions. The difference in ion concentration creates an electrochemical gradient that allows for nerve impulse conduction. Nerve impulses from motor neurons stimulate muscle contraction. I explain this to illustrate why our total sodium-to-potassium ratio should be 3:2.

However, if you’re losing more sodium because of factors related to sweating, physical activity, and eating a whole food or low-carb diet, you may need something closer to a 5:1 ratio. This ratio boosts your sodium intake to account for losses in sweat and urine, and it accounts for the possibility that you’re already consuming adequate or optimal potassium in your diet. (More on potassium-rich foods coming up, so keep that avocado within reach.)

If you’re not sure of your individual sodium needs based on your activities, climate, and diet, you can use LMNT’s handy Sodium Intake CalculatorOpens in a new tab as a guide.

What Should You Drink When Dehydrated?

To consume fluid and electrolytes in optimal amounts, you have several options.

Try a DIY electrolyte mix

This recipe includes a 5:1 sodium-to-potassium ratio. Mix the following ingredients.

2,500 milligrams sodium chloride (for 1,000 milligrams sodium),
385 milligrams potassium chloride (for 200 milligrams potassium)
390 milligrams magnesium malate OR 265 milligrams di-magnesium malate (for 60 milligrams magnesium)

Then weigh each serving. If you used magnesium malate, one serving weighs roughly 3.3 grams. If you used di-magnesium malate, one serving weighs about 3.15 grams. Add your serving to 16 to 32 ounces of water and enjoy. For flavored versions, check out LMNT’s recipesOpens in a new tab, all of which use natural ingredients.

Try LMNT or another electrolyte supplement

If you’re not the DIY-in-the-kitchen type, LMNT has your back. Well before I ever started writing for LMNT, I filled my pantry, purse, and travel bag with the company’s flavored stick packs. They contain optimal amounts of electrolytes for me, and they don’t contain added sugar, which I prefer to skip. But remember: LMNT is likely unsuitable for people on sodium-restricted diets for issues like heart failure or uncontrolled hypertension. Always consult your healthcare provider(s) for personalized advice.

What about plain water or sports drinks?

The experts I interviewed have a few caveats about what not to use to rehydrate fast.

Plain water

“Drinking plain water without electrolyte replenishment,” Dr. Israetel says, “carries risks such as failure to replace critical electrolytes (particularly sodium, potassium, magnesium, and chloride), and active dilution and flushing of electrolytes through excessive plain water intake, potentially leading to conditions like hyponatremia (dangerously low blood sodium levels).”

Dr. Nystrom agrees and shares an example he encountered. “I saw a relatively healthy 30-year-old female who had terrible acid reflux so had been chugging cold water for hours because that was the only thing that relieved her pain,” he says. “Her sodium levels were low, as she had overhydrated. This is an uncommon example but drinking plain water to compensate for dehydration can be dangerous.”

People who are most at risk for hyponatremia include those who:

Work outside in hot weather, especially people who are engaging in physically demanding activities, such as construction, landscaping, and more
Engage in strenuous or endurance activities
Have underlying health conditions that affect their electrolyte balance, including adrenal insufficiency, kidney disease, or diabetes

“For these populations, deliberate electrolyte replenishment is essential,” Dr. Israetel says.

Sports drinks

How about those sports drinks, though? The experts say they aren’t enough. “One of the most common myths I see in the ER,” Dr. Nystrom says, “is that patients (and parents of sick children) think that Gatorade, Pedialyte, etc., actually rehydrate.” However, the math doesn’t math for these. “None of those drinks actually have enough electrolytes to compensate for losses from sweating or gastrointestinal losses (vomiting and diarrhea),” he adds.

“The volume of sports drinks you would have to drink to replace electrolytes is counterproductive because of the high volume of water-to-electrolyte ratio in those products.”

Your Rehydration Checklist

If you are experiencing mild to moderate dehydration, you can use this checklist or protocol to address the issue.

Sip one glass of water with one electrolyte packet to start. Add a pinch of salt to water if you do not have electrolytes available, but avoid plain water for two hours.
Watch for symptom improvement within one to two hours, and seek help if your symptoms are not improving.

What the Science Says About Hydration Speed

When dehydration occurs, how fast can you rehydrate? “Rehydration speed depends significantly on severity and individual physiological factors,” Dr. Israetel says. “Factors influencing rehydration speed include electrolyte balance, fluid type, digestive health, and ambient environmental conditions.” But he offers the following general guidelines.

Mild dehydration (1% to 3% body weight loss): With adequate fluid and electrolyte intake, rehydration typically occurs within about 45 minutes to one hour.
Moderate dehydration (3% to 6% body weight loss): Recovery usually requires focused rehydration efforts over approximately one to two hours, accompanied by adequate electrolyte replacement to ensure effective cellular hydration.
Profound dehydration (>6% body weight loss): Significant dehydration, as commonly seen after prolonged endurance events or in extreme heat exposure, may require upwards of several hours (three to six or even more) of diligent fluid and electrolyte replacement. In severe cases, IV fluids may be necessary.

Best Practices for Staying Hydrated

A good practice regarding hydration is to do your best to avoid getting dehydrated. Some situations, such as my migraine fiasco, can make this complicated. But I’m super diligent now to stay as hydrated as possible to thwart another emergency.

Here are a few strategies to consider for maintaining hydration throughout the day:

Incorporate water-rich foods, including cucumbers, melons, tomatoes, celery, citrus fruits, and more.
Eat potassium-rich foods, including avocados, bananas, oranges, sweet potatoes, spinach, broccoli, squash, beets, and certain beans and legumes.
Sprinkle your favorite type of salt on your food — only about 15% of the sodium in your diet comes from the salt you add during cooking or at the table.
Add a pinch of salt to your water when the mood strikes.
Hydrate before spending time in the heat or before a workout by consuming water with electrolytes.
Rehydrate after being in the heat or working out by consuming water with electrolytes.
Drink fluids and electrolytes during a workout — the recommendation from the American College of Sports Medicine and the National Athletic Trainers’ Association is to consume about 200 milliliters (about 7 ounces) of fluid every 15 to 20 minutesOpens in a new tab.
Consider a magnesium supplementOpens in a new tab — up to 50%Opens in a new tab of people in the United States may be deficient in this mineral that helps the body hold onto water.

"Best Practices for Staying Hydrated Incorporate water-rich foods (like cucumbers, melons, tomatoes, celery, citrus fruits) Eat potassium-rich foods (like avocados, bananas, oranges, sweet potatoes, spinach, broccoli, squash, beets, and certain beans and legumes) Sprinkle your favorite type of salt on your food Add a pinch of salt to your water Hydrate before/after spending time in the heat or before/after a workout by drinking water with electrolytes Consider a magnesium supplement"

Keep in mind that staying hydrated does not prevent all concerns with working or working out in the heat. “Those are different processes going on in the body,” says Dr. Nystrom, “and although adequate hydration is helpful, hydration alone does not prevent heat exhaustion or heat stroke.” Acclimatization, clothing choices, and environmental monitoring are all important in avoiding heat stroke, which is a neurologic emergency — not just a symptom of dehydration.

Key Takeaways

Your body becomes dehydrated when you lose too much fluid for it to keep functioning properly, resulting in potential symptoms of fatigue, lightheadedness, thirst, muscle cramping, and more.
Fluid loss can also flush out your body’s electrolytes, which are crucial for nerve and muscle function and more.
To rehydrate fast, you’ll need to consume fluid with an optimal amount of electrolytes, but if you’re experiencing severe dehydration, you need medical attention.
Your speed of rehydration will depend on several factors, including why you’re dehydrated and how much fluid and electrolytes you’ve lost.

FAQ

What is the quickest way to cure dehydration?

The quickest way to cure severe dehydration, which is a medical emergency, is with IV fluids. The quickest way to cure dehydration on your own is to consume water with an optimal amount of electrolytes, including sodium, chloride, potassium, and magnesium.

How long does it take to rehydrate your body?

Rehydration can take 45 minutes to several hours, depending on how dehydrated you are, your electrolyte status, why you became dehydrated, and more.

How do you hydrate your body asap?

To hydrate your body asap, consume water with optimal amounts of electrolytes.

What are two warning signs of dehydration?

There are many more than just two to watch for! Key warning signs of dehydration include, dry mouth or throat, dry skin, fatigue, headache, less frequent urination, muscle cramps, nausea, substantial drops in physical or cognitive performance, thirst, and weakness.