Proper hydration for a half marathon can help ensure you feel good and perform your best. Learn how much water you should drink and how often to feel good during your half marathon.
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Proper hydration begins even before the race when you’re thinking about your half marathon hydration plan.
Like proper carb loading for a race, the days leading up to the race, the night before the race, and the morning of the race, hydration counts.
We’ll take a look at all of these and dive into proper hydration for a half marathon, so you can mold that into your half marathon nutrition plan for success!
General Hydration Guidelines for Running
To start, a general rule of thumb is for an individual to drink half their body weight in ounces of water or other noncaloric beverages per day.
For example: a 160 pound person will need to drink a minimum of 80 oz. per day. Additional fluids will likely be needed before, during, and after exercise.
Staying adequately hydrated is not just a matter of drinking enough fluids, though, as 20% of water intake also comes from food sources.
Read more in our hydration for runners guide.
Hydration Before a Half Marathon
You will want to start off your half marathon well-hydrated and well fueled. Check out our post on what to eat before a marathon – it is similar to a half marathon plan.
Some hydration tips for before your half marathon include:
- 2-3 hours before activity drink 20 oz. water or sports drink
- 10-20 minutes before activity drink 10 oz. water or sports drink
- Pre-hydrate to produce a light-colored urine
You’ll also want to have a plan for when, where, what, and how much fluids and electrolytes you’ll consume during your half marathon.
Hopefully, you’ve already tested out your hydration and fueling strategies during training so you feel confident on race day.
Hydration During Half Marathon
Hydrating during a half marathon will help to keep your core temperature and heart rate low, your muscles fluid and pliable, and minimize fatigue.
In other words, it will reduce the level of effort you exert and improve performance.
Some hydration tips for during exercise include:
- Drink before you are thirsty
- Drink a couple of sips or gulps (approx. 4-8 oz. water or sports drink) every 15-20 minutes. It’s best to drink consistently vs. large amounts at one time, sporadically.
- A sports drink or mix, like Skratch, UCAN or Tailwind, will also provide carbohydrates and electrolytes
- Aim to consume 500 to 1000mg sodium per hour
Make sure you practice and know how to carry your water.
Here are some options for how and when to take in water:
Know the water stops – Most half marathons will provide water and/or sports drinks on the course. If you plan to use what is provided on the course, simply look at the race website to find out what and where (which mile markers) these things will be provided. They are usually listed on the course map page, but you may have to search around the website, if not.
For example, the Rock n’ Roll Arizona half marathon provides water and Gatorade endurance throughout the course. So if you want to use what they provide, you would want to try Gatorade endurance on your own during training.
Or, maybe you want to use the water provided but carry and use your own electrolytes and fueling products. This is totally up to you!
The Baltimore Running Festival half marathon provides water and Gatorade endurance (lemon-lime flavor) throughout the course plus chips, bananas, and Gu gels and chews.
Carry Your Own – Races do sometimes run out of water and/or sports drinks, especially if you are a slower runner or start toward the back of the pack.
Have Someone Bring Water and Pass It To You– If you are lucky enough to have a spectator/friend/family member who can track you and bring you water so you don’t have to carry it, that’s another option.
This is common with pro runners, and specialized drink mixes.
Sample Half Marathon Hydration Plan
Of course, everyone is different and you’ll want to come up with your own unique hydration plan.
Here is an example of a hydration plan for a half marathon with a runner running at a 10-minute-per-mile pace (about a 2:10 finish):
5:00 am – Drink ~20 ounces of water or sports drink
5:30 am – Pre-race breakfast
6:40 am – Drink ~10 ounces of water or sports drink
6:45 am – Bathroom break!
7:00 am – Race Start
7:15 am – Drink 4-8 ounces of water or sports drink
7:30 am – Drink 4-8 ounces of water or sports drink
7:45 am – Drink 4-8 ounces of water or sports drink
8:00 am – Drink 4-8 ounces of water or sports drink
8:15 am – Drink 4-8 ounces of water or sports drink
8:30 am – Drink 4-8 ounces of water or sports drink
8:45 am – Drink 4-8 ounces of water or sports drink
9:00 am – Drink 4-8 ounces of water or sports drink
9:10 am – Finish!!
Total fluid ounces taken in: ~30 ounces before race; ~32-64 ounces during race.
Dealing with Stomach Issues
One very important reason for practicing your hydration and fueling strategies ahead of race day is to try and prevent any race day GI issues.
You’ll want to find your sweet spot for fluid intake as well as electrolytes and fueling. This can take some practice and experimenting with different products.
Practice during training to take in fluids, electrolytes, and carbohydrates. Start on a short or easy run day and know where a bathroom is nearby.
Aim to take in 30-60g of carbohydrates per hour of exercise and take your carbs slowly and with enough fluids.
Taking in too many fluids, too many carbohydrates at one time, or too many carbohydrates without enough fluids can all result in GI issues.
Additionally, different products work well for different runners.
Sports drinks, carbohydrate powders, energy chews, gels, etc. are all different options you’ll want to test out before race day to see what works best for you.
Hydration After 13.1
The race might be over, but your fluid and nutrition needs do not stop here. It is very important to continue hydrating, or re-hydrating after the half marathon.
In fact, rehydrating helps bring down your core body temperature, and is part of recovery after a half marathon.
Some hydration tips for rehydrating post-exercise include:
- Aim to drink 16-24 oz. water or sports drink for every pound of body weight loss during exercise
- Consume salty snacks or foods (pretzels, bagels, soup, etc.) to aid in rehydration the rest of the day
- If you are a salty sweater, make sure you’re taking in enough salt through rapid rehydration drinks or mixes, if necessary.
- Continue drinking throughout the day until your urine is a pale yellow or clear
Many races may have beer or alcohol offered after. While this may be tempting, know that alcohol and running don’t provide many benefits.
In fact, excess alcohol can impair your recovery and glycogen resynthesis.
If you do choose to imbibe, make sure to include adequate water before and between drinks.
Weather and Hydration
It’s important to note that each person has a different sweat rate, which depends on their body weight, genetics, heat acclimatization, and metabolism.
If you are a salty sweater, you probably know it, and need to hydrate appropriately.
One thing that can change a person’s hydration needs is the weather. If you are running a half marathon in hot and/or humid conditions, you will likely need more fluids and electrolytes than you would on a cold day.
Exercise, especially in warm and humid environments, increases fluid and electrolyte needs.
Hydration for running in hot weather and consuming enough fluids must be taken seriously to prevent dehydration that may lead to heat exhaustion, decreased performance, increased perceived exertion, and muscle cramps, to name a few.
Too Much Water Isn’t Always Better
Taking in too much water without enough electrolytes, though, can cause hyponatremia, a serious condition where there is too little sodium in the blood.
Sodium loss through sweating and the development of hyponatremia will primarily occur during strenuous exercise lasting more than 4 hours.
So, perhaps not during a half marathon, but important to know for a full marathon and ultramarathon.
Everyone loses a different amount of sodium in their sweat, from as little as 200mg per liter of sweat to as much as 2,000mg per liter, which is largely determined by genetics.
On a hot and/or humid day, you will want to consume more fluids and electrolytes to avoid dehydration. If you are a heavy sweater or a salty sweater, you will need to consume more fluids and electrolytes to avoid dehydration.
While sweating in hot environments can increase sweat rates and fluid loss, fluid consumption must also be maintained when exercising in colder environments.
On average, a physically active individual should consume about 3 to 4 liters of fluid per day, however, it’s best to work with your sports dietitian or medical care provider to figure out your precise needs or perform a sweat test.
Individuals who train more than two hours per day should be consuming more than 7 or 8 liters per day.
Dehydration and Performance
Unfortunately, it is still somewhat common practice for runners to not carry any fluids with them while running.
Depending on the length of the run, their sweat rate, the weather conditions, etc., this will likely result in dehydration.
Dehydration can decrease athletic performance, increase the risk of muscle injury, and impair recovery between workouts.
It takes a loss of only 1% – 2% of your body’s ideal water content to cause dehydration.
Extreme dehydration can lead to heat stroke, heat exhaustion, and ultimately death, if severe enough and left untreated.
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To mitigate the side effects of dehydration, plan for hydration during your half marathon ahead of time.
Practicing your half marathon hydration plan ahead of time can make a big difference come race day!
Makranz C, Heled Y, Shapiro Y, Epstein Y, Moran DS. [Fluid and sodium balance during exercise–standpoint]. Harefuah. 2012 Feb;151(2):107-10, 126. Hebrew. PMID: 22741213.