How Much Water to Drink During Exercise

Calculating Your Need and Hydration Schedule

Biker drinking from a water bottle
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Anyone who has ever embarked on a routine fitness plan will have been advised to "stay well hydrated" whenever exercising. But what does that actually mean?

Does it mean that you need to drink as much fluid as you lose in sweat? And, if so, how much would that be? Or, would you simply use thirst as an indication of how much and when to drink?

The short and simple answer is that the amount varies based on the individual needs of the athlete. It depends largely on the intensity and duration of the workout as well as other factors ranging from temperature, humidity, and altitude to age, gender, height, and weight.

As generalized as this may seem, there are guidelines that can help determine your appropriate need, whether you are thrice-weekly gymgoer or a high-performance athlete.

Calculating Your Daily Need

Generally speaking, if you train regularly, you would need between a half and a full ounce of water per pound of body weight per day.

You would calculate this based on the intensity of activity for the day. At the low end would be a rest day in which you do little activity. At the high end would a moderate- to high-intensity training day, defined as an activity that raises your maximum heart rate (MHR) by 50 to 75 percent or 75 percent or more, respectively.

The amount of water needed for that day would be calculated as follows:

  • Low-end: body weight (in pounds) x 0.5 = fluid ounces per day
  • High-end: body weight (in pounds) x 1.0 = fluid ounces per day

For example, if you weigh 150 pounds, your daily water requirement would be between 75 and 150 fluid ounces. To determine your need in liters, you would then multiply that figure by 0.03 as follows:

  • 75 fluid ounces per day x 0.03 = 2.25 liters per day
  • 150 fluid ounces per day x 0.03 = 4.5 liters per day

This provides you the general parameters by which to maintain optimal hydration, neither drinking too little nor too much (which can be just as bad for you as dehydration).

When to Drink

Whether it is a training day or rest day, always start your morning by drinking an eight- to 12-ounce glass of water. On training days, you would need to hydrate before, during, and after exercise on the following schedule:

  • Two hours before exercise, drink 16- to 24-ounces of water.
  • 20 to 30 minutes before exercise, drink another eight ounces.
  • Just before exercise, weigh yourself to get a baseline weight.
  • During exercise, drink eight ounces of water every 15 minutes.
  • After exercise, immediately weigh yourself and drink 16- to 24-ounces of water for every pound of weight you've lost.

At the end of your workout, you don't need to replace all of your fluids at once. Start with eight ounces and continue to hydrate gradually over the next half hour.

What to Drink

If exercising at a moderate to high intensity for more than 90 minutes, you will want to consume more than just water. This is especially true if you have saltier sweat. Commercially available sports drinks help replenish glycogen (stored energy) lost during exercise with easy-to-digest complex carbohydrates (like maltodextrin).

For longer, high-intensity workouts, choose a sports drink with 60 to 100 calories per eight-ounce serving and consume eight to 10 ounces every 15 to 30 minutes.

If exercising in extreme conditions for more than three hours, you need to take extra steps to replace electrolytes lost in sweat. These include minerals such as sodium, potassium, calcium, magnesium, and phosphate which your body needs to function normally.

A complex sports drink, NUUN tablets, or electrolyte-rich foods can provide the calories and energy needed for continuous performance. Another option is coconut water, a natural source of carbs and electrolytes minus the added sugar or preservatives. You can even make your own sugar-free sports drink by mixing salt, freshly squeezed lemon juice, sweetener, and sugar-free flavorings with plain water.

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