Hydration Needs for Runners

Hydration plays an important role in our performance and recovery as endurance athletes. Generally speaking, at baseline, women need 2.2L and men need 3L fluid per day. We also need to drink back whatever we sweat out. Understanding how much we sweat is important to nailing hydration. 

Hydration & Performance

Dehydration can greatly impact your running performance because it causes reduced blood volume, increased HR, decreased skin & GI blood flow, increased core temp, and increased glycogen usage. Older research suggested anything over 2% dehydration decreased performance. However, a review of over 770 marathon runners found an average of 3.8% dehydration at the end of a marathon, with the range of 1.6 – 8% dehydration, with some of the faster runners ending the most dehydrated. This suggests we need to know our symptoms of dehydration and manage them accordingly. 

Symptoms of dehydration while running:

  • Decreased performance
  • Inability to hold paces
  • Fatigue
  • GI distress
  • Increased perceived exertion
  • Muscle cramps

Sweat Rate

Average sweat rates for endurance athletes are 0.5 – 2.5 L/hr, and many runners sweat even more than this. Knowing YOUR sweat rate can be a game changer for staying on top of hydration in the heat. Test and re-test in different environments – so you know your sweat rate in the dead of winter vs. a hot & humid summer day. If you haven’t figured out your sweat rate yet, head over to our sweat rate calculator. You may be surprised by how much you sweat!

How to Use Your Sweat Rate Data

Before the Run

Start exercise well hydrated. This means recouping sweat losses from yesterday’s training.

Drink 8-16 oz fluid 1-2 hours before your run. Choose an electrolyte drink if it’s warm or you are a heavy/salty sweater.

Consider hyperhydrating the night before long runs if you are a heavy/salty sweater <something like Skratch Hyper Hydration can be helpful>.

During the Run

We will not and do not want to drink as much as we are sweating. We will end up dehydrated, but drinking minimizes the amount of dehydration to control the symptoms.

Drink 10 – 24 oz of fluid per hour during training over 60 minutes in the heat.  Check out our Hydration page for more information on this.

In the heat, always drink an electrolyte drink or water with salt supplements for runs over 60 minutes. Drinking plain water is unlikely to meet your needs.

Consider sports fuel with more sodium if you are a heavy/salty sweater.

After the Run

Drink 16 – 24 oz of fluid ASAP post-run. Choose water + a salty snack or an electrolyte drink to rehydrate more quickly.

Drink enough to recoup your sweat losses to fully recover. For every 1 pound of body weight you lose while running <aka 16 oz> you have to drink back 20 oz to replace those sweat losses.

Next level: add up the fluid you took during your training. Subtract that from your training sweat loss. Drink that back in addition to your daily fluids throughout the day.

Rehydrate more quickly by drinking fluid with some carbohydrates and sodium. This can be in an electrolyte drink or food.


Runner #1 – Average sweat rate

Sweat loss

16 oz/hour, 19 oz total


5 am – 8 oz Skratch Hydration


6 am – 70 min EZ


8 oz Skratch Hydration + 1 serving Skratch chews


12-16 oz Skratch Hydration (+ daily requirements)

Runner #1 – Heavy sweat rate

Sweat loss

60 oz/hour, 70 oz total


4:30-5 am – 16 oz Skratch Hydration


6 am – 70 min EZ


24 oz Skratch Hydration+ 1 Never Second gel


24 oz Skratch Hydration + 24-36 oz water (+ daily requirements)

Check out our Hydration resource page for more details on hydration, sweat rate & sweat rate calculator.

Up next week on the blog – Sweat Composition – we will discuss the composition of your sweat, break down hydration and fueling products & how to put it all together to optimize your performance!

Disclaimer: The content in our blog articles provides generalized nutrition guidance. The information above may not apply to everyone. For personalized recommendations, please reach out to your sports dietitian. Individuals who may chose to implement nutrition changes agree that Featherstone Nutrition is not responsible for any injury, damage or loss related to those changes or participation.