Keys to staying hydrated

Know how much fluid you need to drink when working out. 

June 4, 2020


Exercise raises our body temperature depending on how long and hard we work out. Sweat is the body’s way of cooling us down. It regulates our temperature and keeps us from getting too hot. 

Sweat is made up of water and electrolytes (minerals that balance the amount of fluids in the body). Sweating can lead to a significant loss of both. In turn, this can cause dehydration and heat illness. 

Dehydration happens when you use or lose more fluid than you take in. To guard against this, know the signs of dehydration. 

Signs of mild dehydration include:

  • Dry, sticky mouth
  • Dry skin
  • Headache
  • Muscle fatigue
  • Decreased performance
  • Urine is darker in color 
  • Constipation

These signs aren't specific to dehydration. They can also be caused by heat illness, including cramps, heat exhaustion and heat stroke.

Signs of severe dehydration include:

  • Extreme thirst
  • Heat illness
  • Mental fogginess
  • Irritability
  • Confusion

People with signs of severe dehydration or heat illness need to be cooled down right away. They should be moved to a cool location and possibly placed in an ice bath. Get immediate medical attention if the person shows signs of confusion or mental fogginess.



Expert insights


How much water do you need to drink before, during and after exercising? In this short video, sports medicine specialist Dr. Jeremy Johnson covers what you need to know.

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Tom Butler: Welcome to IRGs Sports Medicine Update I’m Tom Butler along with Shannon O’Kelly, Physical Therapist and President of IRG Physical and Hand Therapy and our guest Dr. Jeremy Johnson, Sports Therapy physician from The Polyclinic. Dr. Johnson welcome, we’re gonna talk hydration, as a sports medicine physician you’ve seen it, I’ve seen it. You know young athletes particular, they just don’t hydrate before activity, tell us the importance about hydrating, when you need to hydrate and why you need to hydrate.

Dr. Jeremy Johnson: When we exercise or body heat goes up and how cool off is we sweat. When we sweat we lose water, we need to replace that water, and so often times people say I need to drink when I’m thirsty. You don’t want to listen to your thirst, cause thirst is way too late. If you’re already thirsty that means you’re already being dehydrated. Let’s talk about before the game and after the game. So before the game you want to make sure that you’re drinking about 20 ounces of water about 4 hours before, during the game if it’s less than an hour, you only need water and as about 3 ounces of water every 15 minutes. After the game a big way to tell how much water you’ve lost is actually weigh yourself so that means you’ll need to weigh yourself before/after the game. For every pound you’ve lost about 20 ounces of water is good. You don’t need sports drinks until you’ve played more than an hour.

Tom Butler: Dr. Johnson thank you. There you go, everything you need to know about hydration. 

Dr. Jeremy Johnson: You’re welcome, great to see ya.

Tom Butler: If you would like more information on this topic as well as how to contact Dr. Jeremy Johnson go to Polyclinic.com or go to IRGPT.com click on the health experts tab.


How to prevent dehydration

Don't go by thirst alone. Thirst isn't the only indicator of hydration. You could be dehydrated before you get thirsty. 

Weigh yourself before and after exercise. This is a more exact way to check for sweat loss and fluid needs:

  • Well hydrated: +/-1% of body weight
  • Some dehydration: -1–3%
  • Significant dehydration: -3–5%
  • Serious dehydration: -5%

Prepare by taking it slow. If you’re new to exercising in warmer weather, it takes two weeks for your body to adjust and regulate use of water. To prepare:

  • Increase the intensity and length of your workout slowly while adjusting.
  • Exercise in cool areas or earlier in the day.
  • Stay on top of fluid intake. Dehydration is the leading cause of mild and serious heat-related illness.

Rethink your drinks. If you exercise for less than an hour, you only need to drink water. If you work out for more than an hour, choose a sports drink with:  

  • 4–8% carbohydrates
  • 20–30 meg/L of sodium 
  • 2–5 meg/L of potassium

Fluid before, during and after workouts

Before exercise:

  • In hot conditions, drink 16–20 ounces of water four hours before your workout. 
  • Consider an additional 8–12 ounces of water 15 minutes before working out if you’re sweating a lot or if it’s extremely hot.

During exercise:

  • For workouts under one hour, drink 3–8 ounces of water every 15–20 minutes or 16–32 ounces after the workout.
  • For workouts of more than one hour, drink 3–8 ounces of a sports beverage every 15–20 minutes.

For all workouts, avoid overhydrating. This can be very dangerous, even deadly. Symptoms are similar to dehydration and heat illness. To avoid overhydrating, don’t drink more than one liter (33 ounces) of water per hour.

After exercise:

  • Check your body weight.
  • Correct losses within two hours after exercise.
  • For every pound of weight lost, drink 20–24 ounces of water.


By Jeremy D. Johnson, MD, MPH, RMSK

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The information provided is for general informational purposes only and is not intended to be medical advice or a substitute for professional health care. You should consult an appropriate health care professional for your specific needs.