How to Hydrate for Your Next Half Marathon

Runner grabbing a cup of water

As runners, we know that staying hydrated is a crucial component to running well and feeling good. But trying to figure out just how much water you’ll need and how often to drink during your half marathon can be intimidating, which is why we’re giving you all the info right here.

Most half marathon runners should take several small sips of water about every 15 minutes. Taking in 4 ounces of water at that time is ideal – aiming for 2 cups (16 oz.) per hour. More may be needed on warm days and less on cool days, so it’s important that runners listen to their bodies and drink to thirst, which will help avoid dehydration or over-hydrating.

Hydrating during a half marathon doesn’t need to be complicated. Here is everything you need to know about hydration for your next half marathon.

How much water should you drink in a half marathon?

Most people need to take in some fluid for a half marathon, according to Meghann Featherstun, a registered sports dietitian and experienced marathoner who co-hosts the Fuel for the Sole podcast. The amount of water you consume depends upon several factors. Featherstun says that a lot of it depends upon the weather during the race, how long the runner is racing, and other factors that vary from individual to individual.

A general rule of thumb for running efforts lasting longer than 1 hour is that you should aim to consume approximately 4 ounces of fluid every 15 minutes, according to Jen Scott, a registered dietitian, running coach and marathoner. One ounce is approximately equal to one gulp of water.

Aside from that general guideline, when it comes to hydrating during your next half marathon, the most important thing is to listen to your body. By listening to your body and drinking according to your own thirst, you can avoid dehydration and its negative effects on your body and race performance. You can also avoid a dangerous and potentially fatal condition called exercise-associated hyponatremia, which is caused by drinking too much water, beyond thirst, when you’re exercising.

How often should you hydrate during a half marathon?

Running coach and Ready.Set.Marathon‘s founder, Jane Springston, recommends drinking “little and often” during your half marathon. Taking small sips of water at most water stations will achieve this. Avoid chugging or consuming large quantities of water at one time, to avoid a sloshing feeling in your stomach when you run, or worse, digestive upset. Make sure that you have practiced hydrating during your training runs, possibly even simulating the timing of when you drink, because you never want to do anything new on race day.

Some coaches recommend starting to hydrate as early as the first water stop in the race. Coach Jane says it’s generally okay to skip the first and last water stations if the weather is mild on your race day and you go into your race fully hydrated. However, if the weather on race day is warm to hot (or you just feel like you need to hydrate early), then plan on taking water at the first water station.

As mentioned earlier, the most important thing you can do is listen to your body. If you feel like you need water right away during the race, take it!

Can run your half marathon without drinking water?

You can run a half marathon without drinking water…although it’s not advisable in most cases. There are no prizes for people who take the least amount of fluid during a race. Remember that just because you CAN do something, doesn’t mean you should or that it’s going to get the best out of you on the day. Scott shares that well-hydrated and well-fueled athletes outperform those who are dehydrated and under-fueled.

Typically, losing more than about 2-3% of body mass from water loss during exercise has been shown to decrease aerobic performance for many people, according to this study. And Featherstun shares that 2-3% body weight loss can be a buffer, and means that someone who is planning on running a fast half marathon (in less than 2 hours) on a cool day might be able to get by without taking water during the race. However, someone who is racing on a warmer day, or who is racing for more than two hours – regardless of the temperature of the day – should drink water during their race.

“Measuring changes in body mass is the most accurate way to determine acute changes in your hydration level and sweat loss,” according to a 2011 study in the Journal of Athletic Training. To figure out how much fluid loss you experience on your runs you’ll simply need to compare your bodyweight pre- and post-run.

Here are the steps to take to find your sweat rate:

Step 1: Drink the fluids you’ll need for your run.
Step 2: Go pee.
Step 3: Weigh yourself naked.
Step 4: Head out for a 1 hour run (you’ll probably want to put your clothes back on for this.) You may hydrate on your run but keep track of exactly how much you drink (no food intake).
Step 5: Weigh yourself naked again as soon as you return from your run.
Step 6: Subtract your post-run weight from your pre-run weight.
Step 7: Add back any water you drank during your run.

If you drank 8 ounces of water during your run but still lost 1 pound (16 ounces), your sweat rate is 24 oz per hour (16 oz. + 8 oz.). This means you really should have drank 24 ounces of water in that hour instead of 8. If you’re still confused about the calculation, TrueSport shares a great example. You’ll also want to consider the temperature – if this happened on a hot day, it won’t be the same as on a cold day.

The final number will demonstrate whether you drank enough on your run or not enough. If you weigh more, you drank more than necessary. If you lost weight, you would benefit from hydrating better on future runs. Taking in the proper amount of water will mean you’ll weigh about the same both before and after the run.

This data can guide your own individual hydration strategy so that you can avoid dehydration, and also over-hydration, during your race.

Should you carry water for a half marathon?

Carrying your own water during a half marathon depends upon your own personal preference, and sometimes depends upon the race.

Some races are “cup-free” or “self-supported” and in those scenarios, you definitely want to carry an empty bottle to fill at the aid stations, or bring your own water. Some racers trying to hit a half marathon personal record (PR) might worry about being slowed down by carrying their own water, so they rely upon race water stations. Still others, like my best running friend, like to have control over when and where they take their water, and carry water with them at every race.

RELATED: Carrying Your Own Water in a Marathon: The Good and the Bad

Water Carrying Options

For carrying your own water at a half marathon, I recommend that runners use something hands-free. Carrying a handheld bottle could get uncomfortable or be cumbersome for an entire half marathon.

Hydration Pack: A lightweight hydration pack would be one excellent option for runners who want to BYOW (bring your own water). I use (and love) the TrailMix 7L Race Pack, which is made by Nathan and is a great value. This pack includes a 2 liter bladder. It is highly adjustable and so comfortable that after awhile, I forget I am even wearing it! Plus, who doesn’t like extra pockets to stash your stuff on race day?

Hydration Belt: Another good option for runners is a hydration belt, such as the TrailMix Plus Hydration Belt, also by Nathan. This belt is economically priced compared to most vests. It comes with two 10 oz bottles. A hydration belt is a good choice for someone who doesn’t like the feel of backpacks, or for those very hot races where you want avoid wearing the extra layers of a hydration pack.

Flexible Water Bottles: Or if you have pockets in your leggings or shorts, another great option are these small, flexible water bottles from Fitly. Jane swears by these and uses them for the half marathon – one for just water and the other for her Tailwind endurance fuel.

RELATED: Half Marathon Nutrition – What and When to Eat During Your Race

Should you drink at water aid stations?

Coach Jane shares that it works well for runners to slow down and walk through race water stations to drink their water if not carrying their own. She recommends taking sips of water at most water stations during the race, while of course, also paying attention to your own body’s needs.

While it might seem like a bad idea to walk during a race, going slowly through the aid station helps ensure that you are able to take your water in small sips, avoid spilling or it “going down the wrong pipe”, and avoid crashing into other runners who are also slowing to grab their drinks. Jane explains how she did this in her most recent marathons in this video.

Spending a few seconds to slow down and sip water every couple of miles really doesn’t affect one’s overall race performance. However, if you have nailed a strategy to run and drink your water at the same time, by all means do it!! As long as you’re getting the hydration you need.

What about electrolytes? Do you need them for your half marathon?

Half marathon racers do need to consume electrolytes during their race. Electrolytes are essential minerals, such as sodium, calcium, and potassium, that are vital for your body to perform key functions. Runners most commonly lose electrolytes via sweat and urine. Low electrolyte levels can cause muscle cramps, fatigue, nausea and low energy, just to name a few unpleasant side effects. That’s why runners should replace electrolytes during high-intensity activities lasting over an hour, according to dietitian Scott.

Popping an electrolyte tablet into your water is a great way to get the electrolytes you need while staying hydrated. We recommend Nuun Sport.

However, it’s important not to drink electrolyte sports drinks at the same time you take your sports gels or gummies. Doing so could flood your digestive system with too much sugar at once, causing stomach upset and possibly derailing your race. Make sure to only consume sports gels and gummies with water, as directed on the packaging, and take your electrolyte drinks separately, spaced several minutes apart.

When should you start hydrating before your race?

According to Shape Magazine, the best way to hydrate before your run or race is by drinking plenty of water throughout the day beforehand. Chugging a bunch of water ten minutes before your race starts is not a good way to hydrate!

You can determine your hydration status by checking the color of your urine. Your body is well-hydrated when your urine color resembles the pale yellow color of lemonade. Urine that is the color of apple juice or darker means you need to drink more. You can back off on fluids if your urine is clear.

Dietitian Jen Scott recommends that runners aim to drink around 16 ounces (2 cups) of water in the 1-2 hours before their race. For runners who have less time than that – for example, if you have a really early morning race start time and don’t get up really early – Scott recommends that runners drink approximately 8 ounces of water at least 30 minutes before toeing the line.

What about hydrating after the race is over?

Post-race hydration is also important. You want to make sure that you replace the fluids and electrolytes that your body sweated out during the race. Shape Magazine recommends that racers consume 16-20 ounces of sports drink immediately following a race. Chocolate milk is a top choice among runners for post-race hydration and nutrition as well, as explained here. Monitor the color of your urine (remember, you want it to be pale yellow like lemonade) to ensure that you are staying well-hydrated as you begin your recovery.

By following our tips and suggestions on half marathon hydration, you are sure to have a successful race and feel great at the finish line! Unsure about how to tackle nutrition for your half marathon? Read this next!

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