Hydration Tips for Trail Runners
How to stay hydrated while running for beginners to runners tackling a trail race
July 24, 2023
The author hydrating on a trail run in Colorado.
Most of us conceptually know hydration is important–of course we need water to live–but what we struggle with is knowing how much to drink while we run, what happens if we don’t, and what strategies will help us run at our peak performance. Throw in the added obstacle of running on trails, and your hydrating system can become an even more complicated subject.
As someone with 18 years of competitive running experiences, as well as 5 years of coaching experience, I have experienced firsthand the effects of varying levels of dehydration. Between my years as a D1 college runner, a marathoner and ultramarathoner, and a coach of runners at all levels, I’ve learned from a lot of hydration mistakes and successes.
Now I’m here to help demystify hydration while trail running and hopefully help you not only understand why hydrating is so important, but feel confident and how to hydrate while on the trails.
Related: Best Trail Running Shoes for Men and Best Trail Running Shoes for Women
Read More: Trail Running Gear List
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Unique challenges of trail running
The author on a rocky trail run. Proper hydration is important no matter where you’e running or how far you go.
Proper hydration is always important, regardless of your activity levels and choices. Trail running, in particular, has its own set of challenges that makes staying hydrated all the more important. Typically, running on trails (compared to on roads or at a track) means less likelihood of seeing other people or getting timely help when needed. As trail runners, we need to do everything we can to be mentally present and capable (i.e., able to make quick and wise decisions) while in more remote places.
Trail running also means navigating more physical obstacles–tree roots, rocks, trails that are steep, winding, or narrow, etc.–compared to road running. Our bodies can feel physically and mentally exhausted much more quickly on the trail, and that excess energy means we need more water and electrolytes to stay sharp.
Importance of hydration in trail running
Staying well hydrated on a trail run keeps you safe and helps your pace, speed, brain functioning, and overall mood.
Staying hydrated while trail running keeps a trail runner safe and makes their adventures more enjoyable. Proper hydration ensures cognitive and physiological function and helps you maintain a steady pace.
It’s also important to recognize the signs of dehydration so you can catch it early. Initial signs include dry mouth, unusual decreased energy level, irritability, rapid pulse, and chills. As dehydration progresses, you may notice headaches, nausea, muscle cramps, loss of appetite, and dark or very little urine.
Effects of dehydration on performance
Whether you’re hiking or trail running, dehydration can impact your performance.
Numerous studies have examined the impact of hypohydration, or water deficit in the body, on athletic performance. Notably, lack of hydration affects physiological function, making it more difficult to control physical movements.
Studies noted decreased ability to evenly pace oneself, as well as increased difficulty in controlling perceived effort, causing slower run times and greater effort required. And frankly, from decades of personal experience as a competitive runner and several years as a coach, I know it’s simply not a great time to run dehydrated. In my experience, the body is quicker to cramp up and feel both physically and mentally fatigued, and it’s easier to fall behind (or literally fall).
While the symptoms of fatigue and falling off pace are supported by the studies linked above, the connection between low water and salt intake and muscle cramps seems to be anecdotal, or perhaps at least correlational, according to one study.
Another study found electrolytes to be the fix for cramping, that in fact water without electrolytes was too diluting and made cramping worse. This means staying hydrated involves more than simply drinking water–you need essential minerals like sodium, potassium, calcium, magnesium, and more in order to feel your best.
Estimate Your Water Needs
A hydration bladder (sometimes called a reservoir) with a hose can be a good way to make it easier for you to remember to drink frequently.
One way to estimate your water needs during trail runs is to weigh yourself immediately before and after an hour run. Each pound lost after that run correlates to about 16 fl oz of water lost. So, if you lost 5 pounds during an hour-long run, you need to make up about 80 fluid ounces per hour. If you drank during the run, remember to calculate that in. For example, if you lost 2 pounds despite drinking 16 fluid ounces of water, you actually would have lost about 3 pounds (or 48 fluid ounces).
Divide your hourly rate by four to determine how much fluid you should take every 15 minutes. For long runs (a term that means something different for everyone, but generally speaking, this means a run over 90 minutes–but no one knows your body and its needs better than you), you’ll also want to consider electrolytes or a low sugar sports drink. This will help keep your muscles functioning at their best and prevent cramping. For more information on finding your sweat rate based on body weight and other indicators, you can check out this article on Runner’s World.
You may be wondering how you will carry all this water and electrolytes. Let’s consider some options!
Treeline Review writer Trey French drinking from a hose on a hydration vest during a trail run in the Eastern Sierra.
Carrying water on a trail run
Here are several options for a hydration system for trail runners that works.
Hydration packs
Hydration packs – which are slightly different from hydration vests (more on that below) – are an understandably common vestige in the trail running community. Not only do they have room for water, but they also have pockets for stashing fuel/snacks, gels, keys, a phone, even extra clothing. In fact, I love my Nathan Hypernight QuickStart 2.0 4L hydration pack so much that I wear it on shorter runs, even if I won’t need that much water. It’s comfortable, convenient, and makes me feel less anxious if I decide to go just a little farther than I originally planned.
Hydration packs come with a variety of reservoir sizes, typically ranging from 1.5L-4L. The Nathan Hypernight QuickStart 2.0 4L, for example, has a 4L bladder connected to a long straw that rests near your mouth for easy access. It's also a winner in our Best Reflective Gear for Running in the Dark for times when you may want to escape the heat by running when the sun is down.
Hydration vests
The main difference between a hydration pack and a hydration vest is that while a pack adjusts at the straps (over the shoulder), a running vest adjusts at the side. Vests also tend to have more storage space at the front (though not always).
The two pouches on the front of your running vest will have room for collapsible bottles you can remove and refill. This is nice for folks who want plain water in one bottle and an electrolyte mix in the other. If it's race day, it's also a fast way for runners who will have aid stations or stops to refill bottles, in addition to grabbing calorie and carbohydrate-rich foods. Most packs have ample room in the pack to store more fluids for longer adventures as well.
See our guide to Best Hydration Vests for Running for more information or check out our in-depth long-term review of the Salomon Adv Skin 12 running hydration vest for more on a vest we love.
Waist packs
Another option is the waist pack or belt, which fits around the waist and has a pocket (typically at the rear) for a water bottle. I’ve tried a few designs and found the most success with the FlipBelt Classic Reflective Belt, as the bottle was easy enough to remove and replace while running, and the bottle only fell out once until I got used to how to adjust it. This is a good option for shorter runs, especially if you find a hydration pack or vest too cumbersome.
Some handheld water bottles for running that we’ve tested. Soft flasks are favorites among trail runners.
Handheld water bottles
Handheld bottles have handles so your hands can easily rest around the bottle without fear of dropping it. They can be hardsided–with a form designed to fit inside your hand–or softsided and collapsible, so they get smaller as you drink. Some folks run with these alone, while others use this in addition to hydration packs or vests for longer trail runs. Some folks appreciate the accessibility of this option, especially during races when they want to quickly refill the bottles. It takes some getting used to, though, if you aren’t used to carrying things while you run. Treeline Review writer Trey French likes the Body Bottle III 500ml by Ultimate Direction.
Treeline Review writer Graham Hodge using the Platypus Quickdraw filter to filter a creek in the Pacific Northwest.
Hydration on Longer Trail Runs
Refilling Options
Before heading out on a trail, it’s a good idea to know your hydration options. Is this a trail race with aid stations? Are there potable water sources along the way? Could you find naturally-flowing creeks, lakes or another water source to run through a filter or purifier? Speaking of filters and purifiers…
Water filters
Depending on how long you’re running and where you’re running, it may be worthwhile to pack a water filter or purifying system in your pack. The winner of our Best Water Filter for Trail Running, the MSR TrailShot Pocket-Sized Water Filter, is a lightweight option. Some folks carry purifying tablets or drops, like the Aquamira Water Treatment Drops or the Katadyn Micropur M1 tablets, in case of emergency. In any case, it’s a great idea to bring electrolyte tablets or mixes or sports drinks, as they not only improve your hydration status but they can help mask the taste of filtered water.
The author for a hot summer run in Colorado. In addition to hydration, remember to wear sun protection like sunglasses and sunscreen.
Hydration Tips for Different Weather Conditions
Hydration strategies for hot weather
Hydrating is especially important during hot weather, as you sweat more to regulate your body temperature and thus lose water more quickly. Water loss is even more significant if it’s hot and humid.
While I live in the dry state of Colorado, I spent the first 30 Junes of my life in Indiana (with one of those in Cuba), so I can safely say from experience that the most dangerously dehydrated I’ve ever been has been on long runs when it’s 80 degrees with 90+% humidity. (In fact, I have a specific memory of being 13 miles into an Indiana June long run in college and seriously contemplating jumping in the mucky, nasty canal that runs along a gravel towpath, only to be brought back to my senses when I miraculously ran into my coach. I was so dehydrated I had been hallucinating and wasn’t even sure it was really him at first. Don’t be like college me.)
All that said, we can be smart about staying hydrated on the trails when it’s hot. Of course, carrying a hydration pack/vest/belt or handheld bottles helps. You’ll want to be diligent about intaking water throughout the course of your run, starting before you feel thirsty. Additionally, you definitely want to include electrolytes with your fluid intake.
We lose a lot of salt when we sweat, and it’s vital to replace that. Have you ever finished a run in the heat and found your skin caked in white salt? Have you ever felt your muscles acutely cramp up mid-run? Sodium, chloride, potassium, magnesium, and other vitamins and minerals are lost in our sweat, and electrolyte mixes help replace them.
Aside from carrying liquids on you, another strategy is to have a home base during trail runs. You can loop along trails and return to your car to replace those fluids and fuel back up. You can also set supplies out on the running course ahead of time, but be respectful of the environment and keep in mind things might get moved by other humans, animals, or weather. Cold water and electrolyte-rich drinks and foods at the trailhead are a gift as well; personally, my car is always stocked with a cooler full of coconut water, pickles, potato chips, and a fruit smoothie for the end of long trail runs. Once I started doing this for myself, the game really changed (i.e., I didn’t feel like crap all day after 20+ mile trail long runs).
Additionally, and perhaps this should be the first thing we state: drink plenty of water leading up to your activities. I do not recommend chugging a lot of water immediately before your run, but over the course of the day. Drinking plenty of fluids should become a habit, generally – especially when it’s hot. A well-hydrated body will function better and set you up for success before you even lace your first trail running shoe.
The author on a trail run in the winter. Winter running requires runners to remember to drink, even if they don’t feel thirsty.
Hydration strategies for cold weather
Yes, we lose water when we trail run in the cold, too. In fact, any time we breathe, we’re losing water, so hydration is essential year-round, no matter where you are. When running in the cold, the main strategy difference is keeping your liquids from freezing. Hydration packs and vests are nice because the fluids are close to your body, so depending on how cold it is, the warmth from your body might be enough to keep the water from freezing in your pack. Be aware, though, that tubes freeze easily. You could consider insulated tubes, but in freezing conditions even those may not work.
Another strategy during cold weather is to warm up after a run with a warm beverage. No joke, when I was doing marathon or ultra training runs through cold months, I would bribe myself on miserably cold mornings with the promise of hot watermelon Nuun at the end of my run. I’m also a big, big fan of packing warm beverages in a thermos and keeping them in my car at the trailhead. Hot chocolate with a dash of salt at the end of a cold trail run is *chef’s kiss*.
See our guide to the Tips for Cold Weather Running and our Cold Weather Running Gear List for more details on staying safe and comfortable in cold conditions.
Hydration strategies for trail running at elevation
Running at high elevations (above 5,000’) means breathing more, which means losing more water. It’s vital for folks running at high elevations to intake more fluids than they may think. Pair that with hot weather and you really need to be on your A game. If you aren’t used to running at high elevations, dehydration from high altitude can sneak up on you. You may find your head pounding and your stomach upset before you even realize you’re dehydrated. The kicker is, with an upset stomach, you may feel less inclined to eat or drink anything. But this is when it’s even more important. Use the hot weather strategies to stay on top of hydration–run with water, return to your car or homebase to hydrate, or even place full water bottles along your route if possible.
Becca Downs is a former competitive runner, running coach, and outdoor writer.
About the author / Why you should trust us
Becca spent 18 years as a competitive runner and 5 years as a coach. She’s suffered through some serious dehydration mistakes and learned lessons the hard way so you don’t have to.
More specifically, Becca ran D1 cross country and track for Indiana University—Purdue University of Indianapolis (IUPUI) and continued racing everything from elite miles to an ultramarathon in her post-collegiate years. She earned a USATF Level 1 certification and coached boys and girls high school cross country and track in Indianapolis for four years. Becca then joined the IUPUI women’s distance coaching staff as a volunteer assistant coach in 2020-2021. She geeks out on trail running, track and field, and cries every time she watches a marathon (they’re just so beautiful!). After notching a few small FKTs under her belt in 2020, she was diagnosed with hip arthritis and now channels her passion for running into coaching, writing, creating training plans for her friends, hiking, and running when her hip allows it.
