Here’s Exactly How Much Water You Need While Running in Summer

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I consider myself a true runner through and through. If it rains, I run. If it snows, I run. And if it's 90 degrees and the sun is glaring down, I run. Although I have my training schedule, form, and choice of run-ready kicks like the UA HOVR™ Machina Running Shoes ($150) down pat, I've realized there's quite a bit about how my own body handles my outdoor summer runs that I still don't understand. The biggest question mark looming over my head was this: how much water do I really need to sustain my long runs?

Sure, I know to drink water before my runs, and certainly during a particularly hot and humid day. Yet, when it comes to how much is actually needed to keep my body in fighting form so I don't feel it at mile 18, I realized I was at a loss. As I geared up to begin training for a virtual marathon this fall, I knew I needed to get my questions answered, so I turned to Heather Bauer, RDN, founder of, who also happens to be a health expert for fitness-ready supplement EBOOST.

Although my main motivator for picking Bauer's brain was to make my marathon training more enjoyable as I trudge through summer sweat, I knew I needed to be aware of the performance implications of dehydration.

"Heat and humidity are separate elements that work together to put your body into overdrive as you run," said Bauer. "For runners who train in humid areas, high heart rates and excessive sweating can be daily struggles. If you're not hydrated, your body can't perform at its highest level." She said this is most commonly exhibited in exhaustion, muscle cramps, and dizziness, among other signs.

During runs

Although I always made a point to consume water of some kind during my runs, the matter of "how much" and "how often" still boggled my mind. Too much water and I felt my stomach sloshing. Too little and I could hardly make it through a 5K without feeling weak. According to Bauer, runners outside should drink six to eight ounces of fluids for every 15-20 minutes during a training run. "If you are running in hot and humid weather for more than six miles, make sure you hydrate with an electrolyte drink, not just water," she added.

For pre- and post-runs

But the hydration question doesn't stop just during the run. When running in summer (and training for a marathon), Bauer explained how important hydration is before and after. She suggested an electrolyte drink or water prior to running, noting 16 ounces is ideal if you can get it down at least one hour before your run. However, to avoid sloshing, she explained to stick to only six to eight ounces about 15-30 minutes before your run.

For post runs, Bauer explained to me that you need to think of your hydration in terms of how much you lose during your long training run. "Percentage of water loss is determined by the number of pounds you lose divided by your starting body weight," she said. "If your calculated percentage is greater than one percent, you are dehydrated." To combat this, she said to plan to drink one mL of fluid for every gram of lost body mass. For example, if you are down two pounds after running, plan to drink 32 ounces of fluids (aka 16 ounces for every pound you lose) after your run. She also suggests that looking for something with electrolytes is ideal for recovery.

Keep consistent outside of the workout

As a marathon runner, my training goes far beyond my long training runs. From what I eat leading up to my longer runs to what I wear, I have to keep a lot in mind — including hydration. The day leading up to a long run, Bauer suggested consuming a liter of water by lunch and your second liter by 3 p.m. She also suggested investing in a BPA-free water bottle with a reusable straw, and a timed reminder to make getting the right amount easy.

"It is also important to note that since many plan their long run on a weekend [and] weekends are more social, you should not drink alcohol the night before a long run because this will dehydrate you much more," she said. If you are going out, she suggests drinking sparkling water with lime or lemon instead, to stay hydrated.