How Much More Water Do Runners Need in the Heat?

Ashley Lauretta
by Ashley Lauretta
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How Much More Water Do Runners Need in the Heat?

You’ve probably heard you need to drink eight glasses of water a day. Or you’ve heard you should drink half your weight in ounces per day. Or you should just let thirst be your guide. With so many different guidelines floating around about proper hydration, which one is the right one — and do you need to change your habits depending on the time of year and the heat index?

We talked to some experts to find out why daily water intake is such a debated topic and what you need to know about staying hydrated during the summer.


In 2004, the Institute of Medicine of the National Academies released a report stating women need about 91 ounces of water per day and men need about 125 ounces of water per day, from both food and beverages. Rather than giving a specific guideline, however, the Centers for Disease Control and Prevention simply states that by drinking when thirsty and with meals, most people are adequately hydrated. Amidst all of this, there are studies saying a large percentage of Americans are chronically dehydrated.

“You may have heard the general recommendation to drink 64 ounces, 2 liters or eight 8-ounce glasses of water per day,” notes Claire Shorenstein, RD, CDN, owner of Eat For Endurance. “That’s a great goal, however you have to keep in mind that everyone has different sweat rates, varying levels of physical activity, and of course differs in height and weight, all of which affects how many ounces of fluid you need per day.”

Because of this, Shorenstein says the better approach is to take your weight in pounds and divide it by two, giving you the number of ounces of water you should aim to drink per day. Stephen Pribut, a sports podiatrist in Washington, D.C., and past president of the American Academy of Podiatric Sports Medicine — a runner himself — admits there is no great way to measure small amounts of dehydration. He agrees water needs vary by person and change based on health and activity level.

“Thirst is one of the signals of dehydration,” Pribut adds. “Some do not pay attention or have a strong enough response to thirst. [For example,] those over 50 — and especially over 65 — have a diminished thirst response.”

Shorenstein reminds us water is an essential nutrient and confusion between hunger and thirst are possible when we don’t have enough. So not only does it affect performance, but also other behaviors.


Summer brings higher temperatures, humidity and sweatier runners. This is the simplest explanation as to why you should up your water intake (and not just when you are running). Pribut notes that due to sedentary office jobs — many with air conditioning — you may not substantially need more, but even with this benefit those office jobs do come with a downside, as well.

“With minimal water available in many offices and yet a coffee bar on many urban corners combined with an increase in consumption of caffeine-based drinks, we are increasingly susceptible to some amount of dehydration,” Pribut notes. “Although some note that coffee is not purely a water-losing proposition since it is fluid, plain water is best for replacement (or a sports drink while exercising).”

Shorenstein echoes this, noting that many of her clients say they are either too busy and forget to drink water or, if running, don’t want to have to make too many bathroom stops. However, monitoring the color of your urine is one of the simplest ways to measure hydration. As you sweat, remember you are not only losing fluid but also salt, so while you do want to drink water, runners also want to replace electrolytes on the run (either in the form of a sports drink or in a tablet/powder added to water) and post-run (with food and water).

“Hydration in the complete sense of the term thus means consuming both fluids and electrolytes to replace these losses,” shares Shorenstein. “When recovering post exercise, consuming a normal, balanced meal along with plain water should allow you to consume adequate electrolytes without having to turn to sports products, since many foods naturally contain electrolytes.”


Remembering the vital fact that many foods contain water can help you up your hydration, especially during the summer months. Pribut advises turning to juicy foods such as salads and fruit, which have absorbable fluid in them. The important thing is to find a balance and remember there is a reason coaches advise runners to take it slow once temperatures rise; it takes our bodies a few weeks to adjust to higher temperatures. This adjustment doesn’t just affect our performance; it’s also for our overall health.

“Those days when you are out more, exercising more, it is warmer and humid and you are perspiring more are certainly days when you need to increase your fluid intake,” adds Pribut. “The recommendation is approximately 2–3 cups of fluid per hour. Be careful not to overdo it; adapt to the conditions slowly.”

Should you want to make it more of an exact science, you can do a sweat test to determine how much sweat you produce during a run. Shorenstein does this with her clients, letting them know exactly how many ounces they need to replenish to be adequately hydrated.

“On average, people lose 24–32 ounces of sweat per hour,” she shares. “You can determine your own sweat rate by weighing yourself before and after an hour of exercise, while keeping track of how many fluid ounces you consumed during that hour. For every pound you lose, that equates to 16 ounces of fluid that you lost.”

With this equation, if a runner lost a pound and drank 16 ounces of water during an hour of running, the sweat rate is 32 ounces per hour; meaning 32 ounces of water is what needs to be replaced. Knowing this number can help prevent overhydration — which is also possible — and can lead to low blood sodium.

It’s vital to understand hydration is important to our overall health and can impact more than just performance. Pribut notes that even when you aren’t exercising, you still need to think about your fluid needs. He urges runners to remember hydration it is one piece of our overall health, however, and like nutrition and sleep, shouldn’t be our only focus but one piece of the larger puzzle.

About the Author

Ashley Lauretta
Ashley Lauretta

Ashley is a journalist based in Austin, Texas. She is the assistant editor at LAVA and her work appears in The Atlantic, ELLE, GOOD Sports, espnW, VICE Sports, Health, Men’s Journal, Women’s Running and more. Find her on Twitter at @ashley_lauretta.


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