The Ultimate Guide To Hydration for Runners


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Hydration is always a “hot” topic (pun intended) for runners. Regardless of the weather, hydration is the number one factor that will influence your race time. You need to find the sweet spot between not drinking enough and consuming too much. Both can cause your runs to go south in a hurry.

I’m calling this post the ULTIMATE GUIDE TO HYDRATION because it’s 2500 words and I hope it helps you develop a hydration plan that improves your running.

I’ve divided this article into several sections:

Part 1: Hydration 101 and Pre-Exercise Hydration.
Part II: Fluid Needs During Exercise
Part III: Post Exercise Hydration
Part IV: FAQs

Part I: Hydration 101 and Pre-Exercise Hydration

It All Starts With Watershutterstock_226919164
Water is tasteless, colorless, and odorless. Because of its many diverse functions in the body, it is sometimes regarded as the most important nutrient. It is true that you can only survive for about 7 days without water.

There is no debating water is needed for health and optimal performance, however, scientists have a hard time objectively advising runners on exactly how much they need to drink daily. Most textbooks recommend consuming 10-13 cups of water a day. However, we know that during hard training you will need a lot more!

Water: Basic Functions in the Body?
Water accounts for about half of your body mass. Also, you have billions of cells in your body that are made up of 60-70% water! Quite impressive indeed–

Water helps to transport oxygen, nutrients, and waste products into and out of your cells. Drinking water provides numerous electrolytes (ions which conduct an electric current) including calcium, chloride, fluoride, magnesium, potassium and sodium. Water is necessary for the digestion and absorption of nutrients and lubricates membranes in the gastrointestinal and respiratory tracts.

Even though it contains no calories, the fluid portion of the cell is where most of the metabolic reactions involved in energy production occur.

Think of water is your body’s coolant, helping to regulate body temperature during exercise, fever and in hot environments. Water also serves as a cushioning component between joints, in the spinal cord and in the brain.

How Much Water Do You Need Each Day?
To meet your baseline needs, the general guideline is 10-13 cups. Runners and other active individuals will need more. To put this into perspective, that’s ¾ of a gallon of fluid!  The good news is that it doesn’t all have to come from liquid.

Consequences of Dehydration
Failure to hydrate appropriately is a chief contributing factor to poor performance for runners, particularly in hot and humid conditions.

It has suggested that performance declines when you lose 3% of your body weight from water. The physical and mental effects of dehydration include:

  • decreased strength
  • decreased speed
  • decreased endurance
  • decreased energy
  • decreases in cognitive processing

How Much Should I Drink Before Exercise?
As mentioned earlier, drinking 10-13 cups should be enough fluid throughout your day to keep your urine clear.  However, if you are planning a long run, especially in warm conditions you will definitely need to pre-hydrate. The good news is that it doesn’t require as much as you might think.

Two hours before your training session, drink 2 cups of water or sports drink. This allows time for fluid to leave the stomach and the excess to be removed by the kidneys.

The actual guidelines suggested in most sports nutrition resources are 5-7 mL of fluid/kg body weight (1 kg = 2.2 lbs) 2-4 hours prior to exercise.

Here’s an example:

If a person weighs 150 lbs, that weight is 68 kg;

therefore, 7 mL/kg X 68 kg = 476 milliliters of fluid.

Since 8 ounces is 240 milliliters, 476 milliliters is about 16 ounces, or two glasses of fluid.

Simple right? Don’t overthink it!

Finally, consuming some sodium-containing foods or snacks can help retain the fluid. A beverage with very light sodium would also suffice. You should think about this ONLY if runs are at least 90-120 minutes. This is NOT an issue for anything under an hour.


Part II: Fluid Need During Exercise

In this section, I will dive into one of the more controversial issues in sports nutrition– hydration guidelines during exercise. In other words, how much and how often should you drink during exercise. I will also address the role of sports drinks in your training and races.

For peak performance runners should have a basic hydration plan before entering a competition. This plan should have been developed and tested in training, months ahead of your event. There should be NO surprises on race day.

The goal during exercise is to drink enough to prevent excessive water loss and maintain electrolyte balance in the working muscle cells.  Hydration becomes more important as your exercise duration increases.


Hydration needs during exercise can be quite variable depending on a bunch of different factors such as:

  • weather conditions
  • sweat rate
  • exercise duration & intensity
  • type of exercise
  • opportunities to hydrate
  • fitness level

How much should you drink during training sessions?
There has been a lot of debate on this question because the sports drink industry has been driving these guidelines. Where do you think the idea that athletes should “drink ahead of thirst” came from…you guessed it the sports drink companies (or research funded by them).

Even as recent as 2009 the guidelines were to drink 8-10 ounces of fluid every 15 minutes during exercise. So that’s 40 ounces per hour…really.

For MOST people that is way too much.

Over the last two decades, this has led to an increased incidence of a condition called hyponatremia (sometimes called exercise-induced hyponatremia or EIH).

We now realize that everyone needs an individualized hydration plan and the requirements aren’t as great as originally thought. In general, I recommend athletes consume 4-6 ounces every 15-20 minutes (~12-24 ounces per hour).

I also suggest that if you are training or racing for several hours, you should NOT rely exclusively on water . Along with overdrinking, this too can cause problems because your body needs calories to fuel longer workouts.


Water or Sports Drink: Which One Is Best?

To sustain endurance performance ≥ 1 hour, carbohydrate consumption (with a mixture of sugars such as glucose, fructose, maltodextrin, and sucrose) may be beneficial.

Here’s a comparison of common sports drinks.

Drink Comparisions





Carbohydrate consumption at a rate of ~30-60 grams per hour has been shown to be quite effective in maintaining glucose levels for endurance exercise.

If you mix your own carbohydrate solution the concentration matters. It shouldn’t be more than 6%-8% carbohydrate because anything over this may impede gastric (stomach) emptying and cause GI distress.

Electrolyte needs during prolonged exercise are best replenished with fluids containing 460-690 milligrams per liter of sodium and 80-200 milligrams per liter of potassium. Most sports drinks meet these guidelines so no worries there. The only issue would be if you made your own electrolyte replacement drinks (which isn’t hard at all).

I wrote a whole blog post on this topic. To read it click here.

How Do You Calculate Sweat Rate?
For runners doing prolonged training sessions (≥ 2-3 hours) it’s difficult to balance fluid and electrolyte deficits.

Sweat rate varies from person to person due to body weight differences, genetic factors, heat acclimation ability and metabolic (energy production) efficiency.

How many of you out there are heavy sweaters? Me too–

Monitoring pre- and post-workout body weights following exercise is one way to establish how much fluid you should try to consume during your endurance sessions.

To do this, weigh yourself before you exercise. Time your workout and keep track of the amount of fluid you consume. By weighing yourself after you exercise, you can determine how much fluid you lost. This amount can be used to estimate how much fluid you need.

Follow the example below to calculate sweat rate:shutterstock_81966223
a. Pre-exercise body weight      125 lbs
b. Post-exercise body weight    124.5 lbs
c. Change in body weight          -0.5 lbs (or 8 ounces)
d. Drink Volume                           22 ounces
e. Urine Volume                             0 ounces (subtract if you take a pit stop)

Follow the example below to calculate sweat rate
f. Sweat loss (c + d – e)               30 ounces
g. Exercise time                          1.5 hours
h. Sweat Rate (f ÷ g)       20 ounces/ hour

So a good place to start is 20 ounces/hour or 5 ounces/15 minutes

Tweak this volume as needed.


Part III: Post-Exercise Hydration

You’ve finished your workout, now what? It’s time to start rehydrating, with the goal of replenishing any fluid and salt lost from your sweat. But do these post-exercise electrolyte drinks really help speed recovery from exercise? Let’s dive into that question.

Fluids Are the First Step Post-Exercise
The most important aspect of your recovery regimen should be fluid replacement (whether your post exercise drink contains electrolytes or not). As a general rule of thumb, you should consume 2 to 3 cups of fluid for every pound lost in your training session.shutterstock_288163250

If after several hours you still haven’t urinated, then keep drinking!

For example: You run in the heat for 1.5 hours and lose 4 lbs.

That’s 8-12 cups or 64-96 ounces (2-3 L) of fluid you should replace in the post exercise period.

Ideally fluids are best absorbed by your body post-exercise when ingested gradually, as opposed to a single large amount. So don’t try to guzzle all of this fluid at once!

It’s usually not a problem to rehydrate throughout the rest of your day in preparation for your next training session. However, if rapid recovery is needed (<24 hours) or you lose more than 5% of your body weight in a training session then rehydration becomes more difficult.

For instance, let’s say you are doing double runs—one in the am and another in the pm—rehydrating is key to performing well in that second workout.

There are two ways to ensure you have rehydrated.

  1. The scale
  2. Urine output/color

We have talked about how to hydrate without the scale in a previous post.

Does Coffee, Tea, and Soda Help Replenish Fluid Needs?post exercise electrolyte drinks
The answer might surprise some of you but the answer is YES!  Even though these beverages contain caffeine they still help to meet your fluid needs. Research suggests that unless you consume more than 6 mg of caffeine per kilogram of body weight there is NO diuretic effect. So, for a 150 pound individual (68 kg) that would be over 400 mg of caffeine.

Post Exercise Electrolyte Drinks Are Helpful but Not Required
For exercise sessions, less than 2 hours the resumption of normal meals, snacks, and beverages is usually sufficient to restore hydration levels and replace electrolytes. Don’t feel like you need to down copious amounts of Gatorade to restore sodium levels. Most commercial sports drinks are generally weak sources of sodium anyway.

The best bang for your buck is to consume real foods. Examples could be a bowl of soup, a turkey sandwich with pretzels, or other foods that contain sodium (pretty easy huh).

One thing we know is that salty food makes you want to drink more— which helps your fluid consumption.

For longer sessions (>2 hours) you could include a post-exercise electrolyte (sports) drink. The benefit of a sports drink is that calories and electrolytes get onboard quickly which is great if you have another hard training session the next day. If training will be easy the following day then you could skip the electrolyte drink and reestablish electrolyte balance from eating real food.


Part IV: A Few FAQs

Q: When and how much should I drink before a run of 30 minutes to an hour?

A: A run of this duration really doesn’t require an emphasis on hydration. Just focus on your daily hydration needs. We’ve said 10-13 cups of fluid for most is great start. Another way to estimate daily needs is 1 milliliter per calorie consumed. So, if you are eating 2,000 calories per day that’s 2,000 ml or about 9 cups.

Q: During the week of preparation for a half marathon how much water should one consume?

A: At this point you shouldn’t do anything different. Drink to thirst during the week but DON’T over hydrate. Remember you will be tapering so less miles means decreased fluid needs. Drinking too much will just keep you up all night peeing. Follow the guidelines described in this post and you should be good.

Q: I hate running with stuff in my hands AND belts that slosh around, so I more or less build my routes around water fountains or leave a bottle on my porch.

A: I hated running with a bottle too…but you get used to it. I actually really enjoy it now, it’s liberating. Like you, I would plan my running route then drive out to stash fluid/gels for later. The handheld water bottle by Amphipod is my favorite. Not only will it hold your fluid but also gels, a car key, whatever. If you are on a trail run, I will throw some toilet paper in a ziplock (just in case).

I would NOT recommend a running vest, unless you are a trail runner who is going out for hours at a time. In my opinion its just not needed.

Handheld bottles hold plenty of fluid and can be refilled easily. If you can find a water hose on the side of a house or business, that works.

Q: I have been making my own hydration concoction of : 12 oz water , tablespoon honey , lemon juice and sea salt – about 1/2 teaspoon . I this a sufficient supplement to plain water on high humidity days?

A: Making your own drink works. I’ve personally tried your concoction above and thought it was pretty terrible. It can work, I just don’t like hoshutterstock_62742070ney. Unless you are running over 3 hours sodium is not an issue, even on the most humid days. We have hormones that help us conserve fluid and sodium.

In one of my most popular blog posts called DIY Sports Drinks, I show you how to make your own. Give it a try!

Q: Is BEER a  recovery beverage?

A: Why of course! 🙂 When consumed in moderation there’s nothing wrong with enjoying an adult beverage to two. But remember alcohol is a diuretic so too much will have the opposite effect!  


Post Summary
Staying hydrated is paramount to your success as a runner. The best hydration strategy starts by ensuring you are meeting your daily fluid needs along with being hydrated prior to a training session.

Achieving peak endurance performance requires the proper estimation of fluid needs before, during, and post-exercise. It’s not difficult but if you don’t get it right it will hinder performance.

It is vital that athletes create an individualized hydration plan that factors in sweat rates and daily fluids. Also, as exercise duration increases beyond several hours electrolyte supplementation may be required, especially for heavy sweaters. Post-exercise make rehydration a priority along with replenishing sodium lost from sweat.

The guidelines I’ve provided above are a great starting point but it’s up to you to modify as needed.

Now for your homework:
Develop your own a hydration regimen and email it to me. If you need a hand, let me know–I’d love to help!






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