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Guide to Marathon Hydration (Before, During and After)

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It's no secret that your marathon hydration strategy can make or break your race, but very few athletes have the correct knowledge when it comes to race hydration.

Proper hydration during your marathon is critical to your race success . . . and your recovery. This article will give you the details you need to be properly hydrated before, during, and after your event.

Man and woman runners drinking water

Hydration Before the Marathon

Before you start your race its important that you're fully hydrated. Drinking water at will is helpful, but to be fully hydrated prior to your marathon you'll need to pay closer attention to your body and routines.

Once you begin sweating during your race, you'll be fighting against electrolyte and fluid loss. By starting off hydrated, you'll not only prevent severe dehydration during your race, but you'll also maximize your blood volume and assist your cardiovascular function. 

By being fully hydrated, you'll reduce fatigue and allow you the opportunity to sustain your race pace.

Here are a few things to focus on when it comes to pre-race hydration:

Avoid Drinking Too Much Water - If you drink too much water before your race, you can dilute the sodium in your body. This can result in hyponatremia, which causes your cells to swell, and it can even be life-threatening.

Drinking too much water shortly before a race can also cause you to feel uncomfortable. The liquid will slosh around in your stomach, and you'll likely need to find a bathroom during your run.

Pro Tip:  Two hours before your race you should drink about 16 ounces of water (or electrolyte drink) with a snack or meal. Then about fifteen minutes before the race starts, drink 6 to 8 ounces of water or electrolyte drink.

Drink Enough Electrolytes - The night before your race, it's a best practice to consume an electrolyte drink that has a high sodium level. This will increase your blood plasma volume.

Add Sodium to Pre-Race Drinks - Your body will tap into your muscle's glycogen to provide energy. Sodium will help transport the glycogen through the body and will also help absorb fluids into your blood, as well as help you maintain proper blood glucose levels.

Having this reservoir of extra fluid means your body will have more to draw on when you begin sweating during the race. You can add extra sodium to your drinks and meals leading up to the race.

There's a lot of great electrolyte drinks on the market. Experiment with a few different ones during your long training runs and see which one works best for you. Many runners enjoy drinking coconut water or a drink like Coco5 which comes in a variety of different flavors and was developed by pro trainers for pro athletes.

COCO5 Clean Sports Hydration Limon Flavor | 100% Natural | 50% Less Sugar | Nothing Artificial | Non-GMO | Gluten Free | Developed by Pro Trainers for Pro Athletes | 16.9 Ounce (Pack of 12)
  • Case of Twelve, 16.9- fluid Ounce Bottles
  • COCO5 is an All-Natural Fitness Drink Made with 100% All Natural Ingredients. Gluten Free, Wheat Free and Vegan
  • Nothing artificial, ever. NO dyes, NO artificial flavors, NO artificial sweeteners, NO high fructose corn syrup, and non-GMO
  • COCO5 has ½ the total sugar of the leading sports drink and contains 5 naturally occurring electrolytes
  • The sports drink is made of a coconut water base, infused with all natural flavors (from fruits & vegetables). COCO5 provides the hydration benefits of coconut water, but doesn't taste like a coconut water
Marathon runners grabbing water at a hydration station

Hydration During the Marathon

During the marathon you'll need to drink at regular intervals. A great way to learn how much you'll need to drink (and when to drink it) is to monitor your training sessions.

If you're well-hydrated prior to the race, you'll likely drink less. But with that said, it's important to remember that you'll need to drink more during the race if you're dehydrated.

Determining your sweat rate will give you a good idea of how much you'll need to hydrate during your race.

Pro Tips:  

  • It's a good idea not to rely on hydration stations as your only source of water. Wear a hydration belt so you can rehydrate at any point.
  • Hydrate based on your sweat rate. If you're a heavy sweater, you may need to drink 16 ounces of water every 15 minutes.
  • Electrolyte drinks are an easy way to consume the electrolytes your body needs during a long run.
  • Along with your hydration, consume some carbohydrates, such as dried fruit and/or sports gels.

What to Drink

Your hydration strategy needs to be personalized to suit your needs. During the months of training leading up to the marathon, experiment with different fluids and run with your hydration pack to determine your hydration needs.

Everyone sweats during endurance races like marathons, but the amount of sodium lost from sweat differs between athletes. Your hydration is an important part of your training and racing. If done incorrectly you could suffer from cramps, dehydration and hyponatremia.

Only drinking water while sweating profusely will dilute the all-important sodium levels in your blood. To combat this, make sure to drink electrolyte drinks during the race to replace any lost sodium.

There's a wide variety of electrolyte drinks designed specifically for running. Experiment with a few different kinds to determine which one works best for you. 

Pro Tip: Train with the same energy drink that your marathon will be serving at their hydration stations. Many marathon race directors will publish this information on their websites, or you can write to the race director directly.

Woman runner rehydrating after race

Hydration After the Marathon

You may think that after you've run your race you don't need to worry about hydration. But it's important that you replace the fluids and electrolytes you lost during the marathon over the next few hours.

Don't trust your thirst. Unfortunately, your thirst is not a trustworthy indicator of your hydration (a good indicator is your urine. It should be clear or light yellow).

Dehydration symptoms include fatigue, muscle cramping, dry mouth, dry skin, and of course, thirst. If you experience these symptoms, you should increase your water and electrolyte intake as soon as possible.

Pro Tip: After your race drink, 16 ounces of water and electrolytes along with some food. We highly recommend determining your sweat rate and drinking 20 to 24 ounces of fluid for every pound lost during the marathon.

Man running in sweaty blue shirt

Calculating Your Sweat Rate

Calculating your sweat rate will allow you to determine how much fluid you lose during your runs. The process is relatively easy, but it does require a little math. However, once you have your sweat rate you'll be able to use it to plan your event hydration.

To calculate your sweat rate you need to: 

  • Weigh yourself before and after your run (divide by 2.2 to convert to kg)
  • Subtract your before weight from you after weight to determine how many kgs of fluid you lost
  • Add in any fluids (mL) you may have consumed during your run
  • Divide by the duration of your workout (ie. 60 minutes)
  • The answer is your sweat rate, which is the amount of fluid (mL) per minute your body loses

Now that you know your sweat rate you can formulate your hydration plan to ensure you consume enough liquid to prevent dehydration. In other words, if your sweat rate is 25 mL per minute, you'll want to make sure you consume 25 mL of liquid for every minute of exercise. 

In other words, if your workout is 30 minutes long, you'll need to 750 mL of liquid to replenish your fluid loss and rehydrate.

Watch the Video

Marathon runner approaching hydration station

What to Drink During a Marathon

During your marathon you'll want to fill your hydration belt and water bottle with liquid to help stay hydrated. Here's a few popular options:


Water is undoubtedly the best liquid to prevent dehydration. For many recreational athletes, water is enough to provide hydration during workouts, provided the workouts are less than an hour long, and weather conditions are cool.

For more intense or longer workouts, or when running in very hot temperatures, water won't be enough to keep you hydrated.


More intense workouts or workouts that last for long periods result in more sweat loss. In these instances, you'll need to switch from water to a liquid that contains electrolytes.

Electrolytes are available in various forms, and you should experiment with a few different types and brands to find one that works best for you: 

Always check the formulation of the electrolyte product you choose. Some have more sodium, potassium, selenium or copper. Different brands also come in different flavors, so experiment with a few until you find what makes you feel your best.

During a marathon, you may want to keep a chewable tablet or gel packet with you, as these are small and easy to carry. You can also carry some electrolyte replacement powder with you and add it to any drink you receive at the water stations along the route.

If you're running a trail marathon, make sure your hydration pack is filled with a drink containing electrolytes to combat any fluid and mineral loss.

Sports Drinks

Many sports drinks contain carbohydrates and sugar, which can be useful leading up to and during the race. The calories in these drinks are easy to digest, and the carbs can give you a much-needed energy boost when fatigue starts to set in.

Sports drinks that contain different sugars (glucose and fructose), as well as electrolytes, are the best options for marathon athletes as they can quickly refuel you.

If you can't stomach gels or chews during a race, then grab a sports drink at the water station or incorporate it into your fueling strategy if you have to carry your own hydration.

Marathon runner crossing finish line

How Elite Marathon Runners Hydrate

A study that investigated the runners at the London Marathon found that although there were several water stations along the way, 12% of the race participants had plans to consume too little fluids, which would put them at risk. This is in spite of 93% of the runners confirming they read the hydration guidelines.

So how do elite athletes hydrate?

The top marathon athletes in the world drink approximately every 3 miles, and they consume and electrolyte gel between the 6 to 9 mile marker and another between the 15 to 18 mile marker.

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