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Ask Mario: How Much Should I Drink When It’s Hot Out?

Staying on top of your hydration in the heat and humidity can be tricky, so keep these key points in mind.



After a relatively mild summer on the east coast, we’re experiencing a late heat wave with temperatures skyrocketing into the 90s last week—not to mention the accompanying high humidity. I’m in the middle of marathon training so I’ve been running long (16-20 miles) every weekend. How should I adjust my hydration strategy in the hot weather? Should I drink more? Or more often? Any advice would be super helpful!


Amanda G.



Having spent most of my life living (and running) in New England before moving to California a few years ago, I can commiserate with the recent late summer temperature surge and the problems it can create around marathon training. As if the weekend long runs weren’t grueling enough!

The important thing to keep in mind is that as runners, we come in different shapes and sizes, which means that we all sweat at different rates and that our individual hydration needs are going to vary as well.

The Mayo Clinic recommends adults consume between 2 and 3 liters, or 70 and 105 fluid ounces (this includes water and other liquids) per day in a temperate climate. Of course, individual adjustments need to be made for age, activity level, sweat rate and, in your particular case, warmer conditions. As a general rule, the bigger you are, the more sweat you’ll lose through activity and thus the more fluids you’ll need to replace.

When heat and humidity are high, dehydration is an obvious concern, as is hyponatremia, a dangerous condition in which sodium levels in the blood get too low. Throughout the year, but especially when it’s really warm out, it’s good practice to have a 20-25 ounce water bottle on you at all times throughout the day and to sip from it regularly. Aim to empty this bottle 3-5 times per day depending on your size and sweat rate. Be sure you’re taking in electrolytes (sports drinks, enhanced waters and electrolyte drink mixes are good sources) in addition to water in order to maintain proper fluid balance and muscle function in the body. While running on a hot day (70-plus degrees), carry fluids with you or run a route where there are plenty of drinking fountains (“bubblers” where I’m from).

Before you even fill up the bottles in your hydration belt for a run, however, make sure you’re hydrating well throughout the day, not just when you’re out running. In her book Sports Nutrition for Endurance Athletes, nutritionist Monique Ryan recommends drinking 16 ounces of fluid before bed the night before a race, long run or big workout. In the 2–3 hours before a long run or race, she suggests runners aim to consume 16–24 ounces of fluid in the form of water, sports drink, or juice. This will ensure that you’ve topped off your tank while giving your kidneys plenty of time to process fluids.

Ryan also advises that when running over 90 minutes, whether in training or during a race, runners should start drinking early and consume 4–8 ounces of fluid every 15–20 minutes in an effort to stay on top of hydration levels. For some, this may be a bit much and cause feelings of fullness late in a race or long run, so use your long training runs as an experiment to find out what works for you.

So now that you know when to drink, the question becomes, what should you drink? Again, the answer depends on the runner and his or her individual needs. Over the course of a half marathon, marathon or a really long training run, you’ll lose not only water, but also important electrolytes such as sodium and potassium that are necessary to maintain muscle function. The easiest way to replace those electrolytes lost through sweat is by taking some form of sports drink, which will contain a mix of electrolytes in the form of sodium chloride and potassium, as well as simple sugars that will help keep the muscles fueled and functioning properly.

If the sugary stuff doesn’t sit well in your stomach, however, there are plenty of other excellent options, including sugar-free, low-calorie electrolyte drink mixes, as well as electrolyte pills and salt tablets that, when combined with regular water intake, will keep your electrolyte levels up. If you don’t like the idea of straying too far from water or popping pills into your mouth, basic foods such as pretzels and bananas are chock-full of everything you need to accomplish the same goal.

Staying on top of your hydration in the heat and humidity can be tricky, but keeping these key points in mind will allow you to get the most out of your remaining long runs and set you up to hit your goal on race day.

Hang in there. Cooler fall temps are (hopefully) around the corner!


Ask Mario appears monthly in Competitor magazine and weekly on Have a question for Mario? Submit it here.