Running and Hydration

Runner drinking water in forest
Stanislaw Pytel/Digital Vision/Getty Images

It's at once one of the easiest (drink when you're thirsty!) and hardest (sweat rate? Electrolytes? Hyponatremia?) aspects of running: Hydration. For health and performance, runners need to pay attention to what and how much they’re drinking before, during and after exercise. Here's the lowdown on drinking up.

Why Hydration Matters

Dehydration in athletes may lead to fatigue, headaches, decreased coordination, nausea, and muscle cramping. Proper hydration is critical for preventing heat-related illnesses, such as heat stroke, which can have serious consequences.

Aside from all that discomfort, dehydration slows you down. One study showed that even a "small decrement in hydration status" on a warm day impaired runners' performance.

How Much You Should Drink

The current advice about running and hydration is very simple: Try to drink to thirst. Scientific evidence says that drinking when you're thirsty can help prevent underhydrating (which can lead to dehydration) and overhydrating, which can lead to hyponatremia (low blood salt level due to abnormal fluid retention).

The general rule of thumb for fluid consumption during runs is: Take in 4 to 6 ounces of fluid every 20 minutes.

Runners running faster than 8-minute miles should drink 6 to 8 ounces every 20 minutes. During longer workouts (90 minutes or more), some of your fluid intake should include a sports drink to replace lost sodium and other minerals.

Determining Your Sweat Rate

The above guidelines are broad. It's important to remember that everyone's fluid needs vary. Some people sweat more than others.

To determine how much liquid to take during a run or race, you need to know your sweat rate, which can vary from 1 to 4 quarts per hour. Weigh yourself nude before a timed training run, and then again after. (You can drink during this run, but keep track of how much, and add this to your fluid needs calculation.) One pound of weight loss equals 1 pint of water loss. Calculate your sweat rate and use this to determine your fluid needs during a run or race.

For example, if you lose 1 pound during an hour run, that's 1 pints or 16 ounces in 60 minutes. If you drank 12 ounces of fluids during your run, your total replacement need would be 28 ounces per hour. To replace this, you need 7 ounces of water or sports beverage every 15 minutes.

Note the weather conditions on the day you do this test, and keep in mind that you may need to adjust your consumption if the conditions are different. Do the sweat rate test on another day to see how different conditions affect your rate.

Signs of Dehydration

Be aware of the signs that you need more fluids. Early symptoms include:

  • Thirst
  • Dry mouth
  • Feeling fatigued or sluggish

As dehydration progresses, symptoms can include:

  • Headaches
  • Muscle cramps
  • Nausea
  • Fatigue

What to Drink

There are options beyond plain water for rehydration. Some are only appropriate for longer, more intense runs.

Cold Water

Drinking your water chilled helps cool your body down, which slows sweating (and therefore the associated loss of water). Research shows that drinking cold water or even an icy slush can improve and extend your performance when running. Plus, most people prefer the taste of cold water, so they may drink more water when it is chilled.

Sports Drinks

When you run for more than 90 minutes, especially when you are sweating, you should begin to use an electrolyte-replacement sports drink. Depending on the conditions, you may alternate it with water or switch to only sports drinks at that point.

Sports drinks, such as Gatorade or Powerade, contain electrolytes such as sodium and potassium, the components of table salt. When you are running, your body loses electrolytes through sweat. You've probably seen the salt stains on your running hat and tasted the salt in the sweat running down your cheeks.

Since electrolytes help your body retain fluids and may prevent muscle cramps, you need to replace them. After 90 minutes, you also need to take in more carb calories to maintain your effort, and so a sports drink that provides both carbs and electrolytes is helpful. Some runners find that it's sometimes easier to get their calories through liquids rather than solid foods, especially during the later stages of a long run or race. If you don't care for the taste (or sugar content) of commercial sports drinks, you can make your own.

Runners who don't sufficiently replace electrolytes during long runs or races can risk over-hydration. Hyponatremia, which is low blood sodium concentration, can occur when athletes drink excessive amounts of water and don't replace salt lost through sweat.

Flavored Water

If you don't care for the taste of plain water (even when it's icy cold), you can flavor your water to make it more appealing so you will drink enough. Some water additives also include electrolytes, but many don't. So use caution if you are running for an hour or more, especially on a hot day. You may need a sports drink in addition to flavored water.

Coconut Water

Some runners like to hydrate with coconut water or use it as a recovery drink. It contains both carb calories and some electrolyte micronutrients, including potassium and magnesium. It also contains naturally occurring sugar that could provide an energy boost. However, it does not contain as much sodium as sports drinks do.

Coffee

Some research shows that consuming caffeine before a race or a long training run can help with performance and endurance. And if you depend on coffee in the mornings, it's fine to drink some before an early run.

Caffeine is a diuretic, meaning it can increase the need to urinate. So keep that in mind in terms of bathroom access on your run. But caffeine doesn't increase the risk of dehydration, so you do not have to worry about that. While not everyone can tolerate coffee or other caffeinated drinks before a run (it can cause stomach upset), if you can it is fine to drink it.

Carbonated Drinks

The carbonation in soda can also upset your stomach, causing gas and bloating. So it's usually not a good idea for before or during a run. And of course, the sugar in non-diet soda can promote weight gain. If you are drinking soda, you are not drinking water or some other healthier beverage. However, during endurance events like marathons, some runners like a bit of cola to give them a burst of energy (via the sugar and caffeine).

Hydration Timing

Along with what you're drinking and how much, when you drink matters too. Your hydration strategy will vary depending on where you are in your day and in your run.

Pre-Run Hydration

Especially f you're doing a long run or race (more than 8 to 10 miles), it's important to make sure you're well-hydrated during the few days leading up to your long run. You know you're well-hydrated if you void large volumes of pale urine at least six times a day. Drink plenty of water and non-alcoholic fluids. Not only does alcohol dehydrate you, but it can also prevent you from getting a good night's sleep. It's not a good idea to run with a hangover because you'll most likely be dehydrated when you start running.

An hour before you start your long run or race, try to drink about 16 ounces of water or other non-caffeinated fluid. Stop drinking at that point, so that you can void extra fluids and prevent having to stop to go to the bathroom during your run.

Prior to a run of any length, make sure you're hydrated from the start by drinking at least 6 to 8 ounces right before you begin your run.

Drinking on the Run

You will need fluids every 15 to 20 minutes during your run, so you need to either carry it with you or make sure it is available along the way (say, at a drinking fountain or by running a loop that takes you back to your home or car where you have extra water). Drinking small amounts frequently helps your body absorb the liquid better, and you won't have that feeling of it sloshing around in your stomach.

Reminders

Set a timer on your watch or phone to prompt you to drink. Or use landmarks or mile markers as reminders. One study found that athletes who had a hydration plan and wrote it down drank more than those who didn't have a plan.

If you forget to drink and get behind on hydrating, it's hard to catch up. You may have to walk for a bit to conserve energy and cool down.

Carrying Fluids

If you don't have access to water on your running routes, you'll have to carry your own fluids with you. You can try handheld bottles, packs (like backpacks or vests), or fuel belts; it's a matter of personal preference. However, if you're running in a race, you shouldn't have to because there will be water stops on the course.

Post-Run Hydration and Recovery

Don't forget to rehydrate with water or a sports drink after your run. Some people feel the effects of dehydration hours after their run because they failed to drink fluids after they finished. Weigh yourself again after your run. You should drink 20 to 24 fluid ounces of water for every pound lost. If your urine is dark yellow after your run, you need to keep rehydrating. It should be a light lemonade color.

Common Hydration Mistakes

Staying alert to these common problems can help you stay healthier and more comfortable during your runs.

Drinking Too Little

Make a plan and stick with it. Be careful not to run out of water during a long run. You can't always count on drinking fountains (they can break) or stashing water along your route (someone might take it, or it will get too hot to use).

Drinking Too Much

The issue is not so much taking in too much liquid. It's drinking too much without replacing sodium, which can lead to hyponatremia. If you gain weight during a run, you are drinking too much. Add in a sports drink, salt shot, or salty snack to replace the sodium you're losing when you sweat.

Drinking the Wrong Fluid

As noted, drinking plain water when you need electrolytes could be trouble. It's also a problem to drink something new and different during a race. Work out your hydration plans and preferences during training, or else your performance (or stomach) might suffer.

Gulping Instead of Sipping

When you're running, your digestive system slows down because blood is diverted away from it. So taking giant gulps of water can be hard on your belly. Try small sips instead—even immediately after your run, when you might feel like chugging a whole bottle of water. Take it slow.

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