How Much Water Should I Drink Before, During, and After a Run?

How much does hydration for runners matter? You may have heard varying advice: drink to thirst, you don’t need to carry water on runs, or other suggestions. The science shows that hydration for runners is very important – for both health and performance. 

During exercise, you consume oxygen to produce energy (ATP). However, you produce heat as a byproduct of this process. It’s actually a rather inefficient process; for every liter of oxygen, you produce 16 kJ of heat and only ¼ of it for energy production. As a result, your body has to work to cool itself – done through sweating. 

Most runners sweat in any weather condition. Environmental factors (heat, solar radiation, and humidity) and work rate (higher intensities) will increase sweat rate. If you do not replace enough of the fluids lost through sweating, you will have a fluid deficit in your body – dehydration (sometimes also call hypohydration). 

Hypohydration negatively affects running performance. Even minor dehydration lowers your sweat rate, thus impairing your body’s ability to thermoregulate. This response raises core temperature, which leads to a quicker time to exhaustion. 

Dehydration reduces blood volume. As a result, your heart rate increases to attempt to maintain the same cardiac output. You cannot sustain a higher heart rate for as long, so you either slow down or fatigue sooner (or both). Your body doesn’t deliver enough oxygen to the muscles, which slows ATP production. Additionally, this decreased blood volume increases glycogen usage and alters the strain on your nervous. Together, these physiological changes cascade and lead to a significant decline in performance. 

Dehydration triggers gastrointestinal upset. When you lose fluids without adequate replacement, your body redirects blood flow. Less blood flow goes to the gut, which results in up to a 20-25% reduction in gastric emptying rates. The slower your gastric emptying rate, the more likely you are to experience nausea, vomiting, runner’s trots, or other GI symptoms. (Read this article for more guidance on how to combat the runner’s trots.)

Finally, dehydration poses a serious health risk. Since your body’s ability to thermoregulate decreases, your core temperature can increase to dangerous levels. 

You cannot train your body to run better in a hypohydrated state. Physiological adaptation simply does not work like that. Instead, you need a strategic and customized approach for hydration while running, both in training and on race day. 

How much water should I drink before a run?

If you begin a run in a dehydrated state, you will likely have a rough time. It is very difficult to return to an euhydrated state (optimal hydration status) once you start exercising and losing more fluids. 

As part of your daily hydration, it is recommended to drink about 6-8 mL (0.2-0.3 fl oz) per kilogram of body weight, two hours before your run. For example, a 60-kg runner would need 12 to 18 ounces (360-480mL) about two hours before a run. 

If you are an early morning runner, how much water you drink before a run may be slightly less. Since you have less time between drinking and running, you will aim for slightly less (about 8-10 oz). 

Drinking water while running

Should you drink water while running? Absolutely – especially if your run is longer than 60 minutes in length. Anyone who tells you otherwise does not have a robust grasp of sports nutrition or human physiology. 

If you are well hydrated, you will likely not need water on runs shorter than 60 minutes. However, you may still benefit from fluid intake on runs <60 minutes if exercising in the heat or completing a speed workout. 

Once runs are over 60 minutes, you want to develop a customized hydration strategy based on your sweat rate. Sweat rates vary based on intensity, environmental conditions, acclimatization, fitness level, duration, and other variables. Some runners have low sweat rates (0.3 L/hr), while others have high sweat rates (2.4 L/hr) – and many exist in the middle of the spectrum. 

Broadly speaking, the recommendation of hydration for runners is 10-24 ounces per hour of sport drink, electrolyte drink, or water. (If you drink plain water, concurrent use of salt tablets is recommended to reduce the risk of hyponatremia, or low blood sodium levels.) The more sweat you lose, the higher within this range you will be. 

You can use a sweat test calculator to determine your hourly hydration needs while running. This test does involve weighing yourself, so if weight is a trigger, skip this test or have someone else do the calculations for you. Ideally, you will complete this test in conditions similar to your goal race for accurate data. 

Related: Should You Get an IV Hydration Before a Marathon?

How to carry water while running

Numerous pieces of gear are available for carrying water while running. Handheld water bottles use straps to secure the bottle around your palm, without requiring a constant grip. Hydration vests are a hands-free option that use front-pocketed flasks and/or a back reservoir. Waist belts provide another hands-free alternative, with soft or hard flasks secured on the belt. 

The best way to carry water while running? The one that is most comfortable for you. You may even use different systems of various purposes. For example, you may choose to use a hydration vest for long runs and a handheld bottle for speed workouts and race day. 

How often to drink water while running

The frequency at which you drink water while running matters. Evidence indicates that ingestion of fluids every 10-15 minutes is ideal for high gastric emptying rates. High gastric emptying promotes hydration (since fluids need to enter the small intestine for absorption) and reduces any stomach discomfort. If you drink less often, your gastric emptying can actually slow down – which can then lead to a sloshy stomach feeling. 

How much water should I drink after a run?

One step in the recovery process is rehydration. You want to replace the fluids and electrolytes lost during exercise. (Yes, even if you hydrated during – even with a hydration strategy, you will not replace 100% of your fluid losses during exercise). 

Approximately 16-24 oz of fluid (with electrolytes, particularly sodium) is the general recommendation for fluid replacement after a run. If you want a more customized number, you can aim for 125-150% of your fluid loss. For example, if you weigh 1.5 lbs less after your run than you did before, you need about 24 oz of fluid after (1 lb = 16 oz). 

Other FAQs on running and hydration

How much water should runners drink daily?

Your daily fluid intake is very important. You can’t skip drinking water all day long and then expect to be adequately hydrated from just drinking water before a run and during. So how much water should a runner drink?

For the general population, the daily recommendations are 2.2 L of fluid (water and other beverages) for women and 3.0 L for men. Hydration recommendations for runners are greater, since you need to account for the additional sweat losses to achieve a fluid balance. You know your have achieved fluid balance if your urine is light yellow. (However, if you take B-vitamin supplements, this is not a reliable measure due to how the vitamins alter urine color.)

How does running with water impact performance?

Many runners express concern that carrying their own water in a race will weigh them down. The performance benefits of running with water far outweight any downsides. A few extra ounces will not slow you down – but dehydration certainly will.  This is especially relevant for marathon hydration. You can hit the wall due to dehydration!

Is there a difference in how to hydrate on long runs?

On long runs, you absolutely want to bring fluids with sodium/electrolytes. Aim for 10-24 ounces per hour, sipped at every 10-15 minutes. 

Having a customized hydration strategy (calculated via sweat test) is highly recommended for long runs over two hours. On runs of 1-2 hours in duration, you can either drink based on thirst or follow a customized hydration strategy. 

How much salt to add to water for hydration?

Sodium may get a bad reputation in general health advice, but sodium plays a beneficial role for hydration for runners. Sodium promotes fluid retention, makes sports drinks more palatable, and reduces the risk of hyponatremia. (Hyponatremia is a dangerous condition in which blood becomes too diluted during heavy water intake.) For some athletes, including electrolytes and sodium in their sports drink reduces the occurrence of post-run headaches, nausea, and other unpleasant symptoms. 

The amount of sodium you need during a run depends on your sweat rate and concentration. On average, sweat contains 900 mg of sodium per liter; the range is 300-1800 mg/L. If you are heavy sweater with a high sweat concentration, you need more sodium per hour of a run. 

Broadly speaking, the recommendations are 500-700 mg of sodium per liter of fluid. If you use a sport drink that contains 350-400 mg/16 oz serving, you meet this recommendation. (You can also conceptualize this as needing 400-600 mg of sodium per hour).

 Some runners need more, up to 600+ mg sodium/hr. If you have higher salt needs due to high sweat loss, you can replace the extra sodium by ensuring you replace all your fluids (likely 16-24 oz/hr) with sodium-containing sport drinks. If you have very salty sweat but not a high sweat rate, you can increase hourly sodium intake with salt tablets in addition to your hydration strategy. 

Related: A Quick Primer on Electrolytes for Runners

Nail your running hydration strategy

In summary, adequate hydration for runners includes drinking the appropriate amount of fluids before, during, and after a run. The weather, duration and intensity of your run, and other factors will impact how much hydration you need. Once you start getting enough hydration, you will notice a big difference in how good you feel on your runs! 

Smart hydration for runners practices include:

• 6-8 mL (0.2-0.3 fl oz) per kg of bodyweight, two hours before a run (or 8-10 oz if <2 hours)
• 10-24 oz/hr on a run >60 minutes, based on sweat rate
• 500-700 mg sodium per liter of fluid on runs >60 minutes
• 16-24 oz of electrolyte-containing fluid after runs (based on sweat loss/run duration)

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