How to Rehydrate Fast (and How Long It Takes)

The fastest way to rehydrate from mild dehydration is to drink fluids steadily, in sips if you feel sick: water for most people, plus an oral rehydration solution or another electrolyte drink if you’ve been losing fluid to vomiting, diarrhea or heavy sweating. Cleveland Clinic says you should feel better after five or 10 minutes, and mild to moderate dehydration should clear in less than a day once the cause is dealt with.

Severe dehydration is different: it’s a life-threatening emergency, not something to fix at home. The warning signs are further down.

How do you rehydrate fast?

For mild dehydration, Cleveland Clinic’s advice is simply to take in more fluids by mouth. In practice:

Sip steadily rather than gulping. The NHS suggests starting with small sips if you feel sick. If even sips won’t stay down, MedlinePlus suggests sucking on ice cubes.
Water is enough for most everyday dehydration, after a hot afternoon or a day you forgot to drink.
Add electrolytes when you’ve lost more than water. Cleveland Clinic suggests an electrolyte drink when there’s heavy sweating, vomiting or diarrhea, and a sports drink after longer or intense activity or a lot of time in the sun.
Don’t take salt tablets. MedlinePlus warns they can cause serious complications.
Skip alcohol while you recover, as the NHS advises.

What is an oral rehydration solution, and when do you need one?

Oral rehydration solutions are liquids that contain glucose and electrolytes, usually sold as powders you mix with water. They’re the tool for losses, not for everyday drinking: when you have diarrhea, NIDDK says, you need to replace lost fluids and electrolytes, through water, broths, sports drinks or an oral rehydration solution. A pharmacist can recommend one.

A few people should check first. NIDDK says older adults, people with a weak immune system, and people with diabetes, kidney disease or other health conditions should talk with their doctor before drinking oral rehydration solutions. For infants, keep breast milk or formula going as usual and talk with a doctor before giving one.

For a more general look at when electrolytes matter and when water does the job, see electrolytes vs water.

Does food help you rehydrate?

Yes. About 20% of the water people take in comes from food, according to the National Academies, so meals and soups count toward catching up. Broths are on NIDDK’s list of fluids for diarrhea because they carry electrolytes too. If you have diarrhea, MedlinePlus suggests asking your provider what to eat.

How long does it take to rehydrate?

It depends on how far behind you are and whether you’re still losing fluid:

Mild dehydration: you should feel better after five or 10 minutes of drinking, per Cleveland Clinic.
Mild to moderate dehydration: it should go away in less than a day once the underlying cause is resolved and you’re drinking enough.
A stomach bug: dehydration from a stomach or intestinal virus usually improves on its own within a few days, as the illness passes.

If you’re still vomiting or have diarrhea, you’re refilling a leaking tank, so recovery takes as long as the losses do. NIDDK says to see a doctor if diarrhea gets worse or lasts more than 2 days.

Am I dehydrated? Signs to check

MedlinePlus lists these as signs of mild to moderate dehydration:

Thirst
Dry or sticky mouth
Peeing less than usual
Darker urine
Dry, cool skin
Headache
Muscle cramps

Cleveland Clinic adds tiredness, dizziness or lightheadedness, and constipation, and notes your pee should be a pale, clear color.

Thirst on its own isn’t a sign that something has gone wrong. The National Academies concluded that most healthy people meet their daily needs by letting thirst guide them, along with drinks at meals. “If you’re thirsty, you’re already dehydrated” is one of the myths we checked. A headache is often the sign people notice first; we cover that in dehydration headaches.

Signs in babies and children

Children can’t always tell you they’re thirsty. Cleveland Clinic lists these signs in children: a dry tongue and lips, no tears when crying, sunken eyes, a sunken soft spot on an infant’s head, and fewer than six wet diapers a day for infants, or no wet diapers or peeing for eight hours in toddlers. If you see these, call your child’s doctor.

When is dehydration an emergency?

MedlinePlus says to call 911 if:

The person loses consciousness at any time
Their alertness changes, such as confusion or seizures
They have a fever over 102°F
They show signs of heatstroke, such as a rapid pulse or breathing
They aren’t getting better, or are getting worse, despite treatment

Signs of severe dehydration include very little or amber-colored urine, shriveled skin, dizziness, a rapid heartbeat and breathing, and sunken eyes.

The NHS adds signs that need urgent medical advice: unusual tiredness or a drowsy child, dizziness on standing that doesn’t go away, dark yellow urine or peeing less, a fast heart rate or breathing, and few or no tears in a baby or child. Blue, gray, pale or cold skin, trouble breathing, or confusion could be shock; call 911, and don’t drive yourself.

Who is at higher risk of dehydration?

Some people get dehydrated faster, or notice it later:

Babies and young children. They may be unable to tell you they’re thirsty.
Adults 65 and older, who Cleveland Clinic and MedlinePlus both flag as higher risk.
People who are ill. Fever, vomiting and diarrhea raise losses, and a sore throat or nausea makes drinking harder. MedlinePlus advises drinking plenty of fluids before signs of dehydration appear, and watching closely how much children and older adults drink when someone at home is sick.
People with diabetes or who take diuretics, and people who depend on others to get them drinks.
Anyone in the heat. The CDC lists people 65 and older, infants and young children, pregnant women, people with heart disease, and people working or exercising outside in the heat as at greater risk of heat-related illness. Very active people in hot weather can need 6 liters (about 200 fl oz) or more of total water a day.

How do you avoid needing to rehydrate?

For everyday life, drink to thirst and with meals, and drink more in heat or when you’re active. For outdoor exercise, Cleveland Clinic suggests 16 to 20 ounces one to two hours before, 6 to 12 ounces every 10 to 15 minutes while you’re out, and at least another 16 to 24 ounces afterward. Our workout hydration guide goes into more detail.

If you want a daily baseline to aim for, the hydration calculator gives the National Academies guideline for your sex and life stage, plus an estimate from your weight and activity. Treat the estimate as a starting point; for how much Americans actually drink, see our hydration statistics. Neither “half your body weight in ounces” nor “8 glasses a day” is a guideline; both are myths we checked.

Hydrate raises your goal on hot days and after workouts, so you top up before you fall behind. Join the waitlist.

How to Rehydrate Fast: What Works and How Long It Takes