Hydration for Runners: Your Ultimate Guide for Health and Performance

Hydration is important for everyone, but especially for runners.  Whether you’re pounding the pavement or hitting a trail, there’s a careful balance you need to maintain between drinking enough fluid but not too much.  This can be the difference between optimal performance and having a poor race (or even worse, ending up in the medical tent).  Find out everything you need to know about hydration for runners in this post!

This post was written and reviewed by Chrissy Carroll, MPH, RD, RRCA Running Coach.  This post is for informational purposes only and does not constitute medical advice.  For any questions regarding your individual hydration concerns, consult your doctor.

Note: This post was first published in March 2017 and has been updated in October 2021.

Everyday Hydration

To support overall health (and performance), you’ll want to stay hydrated on an everyday basis.  Each day you lose water through breathing, sweating, and using the bathroom, and it’s important to replace these losses. 

Water has numerous functions in your body, including:

• Keep tissues healthy and moistened (like those of the eyes and mouth)
• Lubricates joints
• Assists in maintaining the correct body temperature
• Prevents constipation
• And for runners, research suggests that dehydration before an event may reduce performance – so it’s wise so stay hydrated daily for your best training and races.

How Much Water Should You Drink Daily?

You’ve probably heard the 8 cups a day rule at some point – is that what you should be drinking?

There’s actually not a perfect answer to this.  Your individual hydration needs likely depend on your weight and body composition.

That said, the Institute of Medicine has made the following recommendations for daily fluid intake:

• Men:  3 liters (about 13 cups) of fluid from beverages
• Women:  2.2 liters (about 9 cups) of fluid from beverages

Water is obviously the preferred choice of fluid here, but you can count other beverages (yes, including a daily cup of coffee!) in this count.

Wondering if you’re drinking enough?  While folks have often been told to check the color of their urine to determine if they’re dehydrated, more recent research suggests this may not correlate well with actual dehydration.

That said, those at the Cleveland Clinic still believe that taking a peek at the potty can be useful. 

If you see that your urine has changed from a light straw color to a dark amber or brown color, it may be a signal that you are dehydrated and an indicator to drink more water (and get some medical guidance).

What About Hydration During a Run?

On to the good stuff – what to do while you’re actually running!  The most important goal with hydration for runners is to prevent both significant dehydration and hyponatremia. 

Dehydration occurs when you lose too much fluid and don’t replace it, which can lead to declining performance and increased risk of heat injury.  Research suggests mild dehydration (around 1-2% of your body weight) is likely not an issue for performance, but significant dehydration – losing more than 3-4% of your body weight – may result in a not-so-great race.

Hyponatremia, on the flip side, occurs when you take in too much fluid and dilute your blood’s sodium levels.  According to Mayo Clinic, hyponatremia can cause serious symptoms, including nausea, vomiting, and disorientation in mild forms, and life-threatening complications like respiratory arrest and coma in severe cases. 

Dehydration is much more common among runners than hyponatremia, but hyponatremia generally presents more serious concerns and complications.

The goal here is balance. 

Ideally, you want to replace enough fluid so that you don’t lose too much weight during your run (again, with >3% possibly causing performance impairments).  But you don’t want to risk drinking too much either, as this increases your risk of hyponatremia. 

How Much Should You Drink During a Run?

This question doesn’t have a generalized answer.  In the past, certain organizations put out broad guidelines like “drink X ounces every 15 minutes” – but we now know these are risky because they ignore the very individualized nature of the runner.

For example, sweat rate can vary based on:

• Muscle mass
• Body size
• Age
• Fitness level
• Medical conditions

Similarly, research has shown that slower runners (>4 hour marathon) or tend to be at greater risk for hyponatremia, and that longer events (i.e. ultramarathon) tend to put a runner at greater risk of hyponatremia than shorter events.

With all of this variability, it wouldn’t make sense to give one blanket recommendation on the exact amount to drink.  The right amount to drink to prevent dehydration and hyponatremia can look very different from one athlete to the next.

Instead, listen to your body when running to determine how much to drink: 

Drink when you are thirsty.  Pull back on the hydration if you feel sloshing in your stomach.

It sounds simple, but a 2015 review supports this method of drinking to thirst.  Drinking more than that did not provide a performance advantage, but could increase the risk of hyponatremia.

This can be easier said than done, though. Sometimes in older adults, the thirst mechanism is blunted and doesn’t kick in as effectively.  Or, a runner can get so excited about the race that they just don’t want to stop to take a few sips of fluid.  Similarly, perhaps the race aid stations are further apart than allows for drinking to thirst.

For this reason, you may also want to conduct a sweat test during training to get a general idea of your needs.

How to Do a Sweat Test

A sweat test is a very simple test that requires nothing more than a scale. 

Ideally, you’ll want to do this test when you’re doing a training run on a day with similar conditions that you expect on race day.  In other words, if the date of the race will likely be warm, try to do your sweat test on a warm day too.

Here’s how to do it:

1. Start by weighing yourself (sans clothes) before your training run.
2. Go out for your run and bring along hydration (either a hydration pack, fuel belt with bottles, or a handheld bottle).
3. When you’re done, weigh yourself again (sans clothes).  Also, take a look at how much you drank from your bottle.  Jot it down.
4. Compare your weight from before and after, and determine the percentage of your initial body weight weight that you lost. The equation looks like this: (weight before – weight after) / weight before = X. Then, X x 100 = Percent lost.

Once you know the percentage that you lost, you can assess it:

• If you lost around 1-2% of your body weight, you’re probably right on track for good hydration.
• If you’ve gained weight, you may be overhydrating, especially if you tend to drink frequently without paying attention to thirst.  Try pulling back a bit.
• If you’ve lost more than 3% of your body weight, you may want to try paying a bit more attention to hydration during your run.  Try focusing more on thirst signals (feeling thirsty, dry mouth, etc) on your next run.

This can be helpful for mapping out approximately how much fluid to carry with you if you’re doing a race without frequent aid stations.  (Since you jotted down how much you took in during whatever length of your training run).

During the event, though, you can (and should) defer to your body’s physiologic cues when in question of whether to drink or not.  If you feel thirst or dry mouth, drink.  If you feel nauseous or sloshing, slow down the fluid intake.

What Should You Drink on a Run?

If you’re exercising for less than an hour, plain water is all you need. 

For comfortable temperatures, many runners may be just fine hitting the street for a 45 minute run without any fluid, and chugging a glass of water afterwards.  For hot temperatures, though, your thirst mechanism may kick in even on a short run – so grab a water bottle to bring along if needed. 

If you’re exercising over an hour, then you’ll want to choose a drink that contains electrolytes (specifically sodium, as that’s the electrolyte lost in the highest volume in sweat). 

There are beverages on the market that can fit your needs (or you can make your own sports drink!).  Electrolyte drinks typically contain just water and electrolytes, while sports drinks also provide carbohydrates.

You do want a carbohydrate source for fuel for exercise lasting over 75-90 minutes.  That may come from your fluid source – like a sports drink – or may come from another fuel source, like gels or shot bloks.

Keep in mind though that slower runners in longer events may either underfuel or overhydrate if only using a sports drink as their source of fuel.  (This is because they may need to drink more to meet the recommended 30-60 grams of carbohydrates per hour, but doing so may cause them to overhydrate.)

[Note: If you’re interested in learning more about taking in carbs on a run, check out this post on half marathon fueling.]

Key Hydration Tips for Runners

Now that you know all the science behind hydration, here is a summary of key tips and some helpful ideas to put it all into practice:

1. Drink regularly throughout the day to stay hydrated on an everyday basis.  If you have trouble drinking regular water frequently, try mixing in seltzer, infused water (like this cucumber mint lemon water), and herbal teas.  Other beverages, like juice and milk, also count towards your fluid needs.

2. Fruits and vegetables with a high moisture content can be a great way of increasing your daily fluid intake.  Try watermelon, cucumbers, strawberries, zucchini, and tomatoes.

3. During a run, focus on your body’s signals when it comes to hydration.  If you feel thirsty or have dry mouth, drink.  If you feel sloshing in your stomach and nausea, consider cutting down on the fluid for a bit.

4. Try a sweat test to see if you’re falling in the right range for hydration during a run.

5. For runs under an hour, plain water is fine.  For runs over an hour, use fluid with electrolytes (or water plus salt tablets).  Experiment with your drink of choice during training!

5. Remember that temperature impacts sweat rate.  On hot days, you’ll lose more fluid, and may want to consider packing a bit more hydration in case you need it.  (Try a fuel belt or hydration pack).

Good luck, runners!  You’ve got this. 🙂

Share:  When it comes to hydration for runners, what’s your strategy?  Have you ever weighed yourself before and after a workout to see if you’re meeting your needs?

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