Hydration Basics

This article is part of our series: Hydration Basics.

The adult human body is about 60 percent water, and even light exercise can deplete that percentage, leaving you feeling crummy and interfering with your athletic performance. So, whether you’re hiking, biking, skiing, running, climbing or simply strolling across town, it’s important to hydrate properly. To help you learn how, this article covers:
 
  • How much to drink
  • Tips for staying hydrated
  • How to avoid improper hydration
 

How Much to Drink

a hiker taking a hydration break on the trail
How much you need to drink depends on a number of factors, such as the activity you’re doing, intensity level, duration, weather, your age, your sweat rate and your body type. A good general recommendation is about a half liter of water per hour of moderate activity in moderate temperatures. You may need to increase how much you drink as the temperature and intensity of the activity rise. For example, strenuous hiking in high heat may require that you drink 1 liter of water or more per hour. As you gain experience, you'll be able to fine-tune how much you drink.

For information on hydrating specifically for trail running, see our article, Hydration Basics for Trail Running.

 

Hydration Tips

a hiker reaching for an easily accessible water bottle
Keep water available: The activity you’re doing will likely determine exactly where you stow your water, but the key is to keep it handy. For sports like hiking, backpacking and mountain biking, a hydration reservoir is an excellent option. If you prefer to use a bottle, stash it somewhere accessible, like a mesh pocket that’s on the side of many backpacks. For running, consider a handheld running bottle, a waistbelt or a hydration vest.

Drink often: Rather than chugging water infrequently, take many smaller sips to continually hydrate.

Replace electrolytes: When you sweat, you lose electrolytes, and if you lose too many, your performance can suffer. If your activity lasts for only an hour or less, this usually isn’t an issue, but when you’re out for longer it’s important to compensate for the loss. Focus mostly on replacing sodium and potassium, but calcium and magnesium are also important. The easiest way to do this is with an electrolyte replacement sport drink. You can buy convenient powders and tablets to pre-mix with water before you head outside or to carry with you while you’re out there. Follow the directions on the packaging for mixing and consuming.

Drink more at altitude: Doing any activity at higher altitude can lead to dehydration. You’re less likely to crave water and feel thirsty at higher elevations, so it’s important to drink frequently.

Drink even in cold weather: You may not feel like taking a swig of cold water on a winter day, but it’s just as important to stay properly hydrated in cold weather as it is in hot weather. Packing along a hot drink can be a good way to keep yourself hydrated.

Pre-hydrate: It’s common practice to pre-hydrate before exercising. A general recommendation is to drink about 17–20 fl. oz. about two hours before heading out.

Rehydrate: Drinking after exercise gets your fluid levels back to normal and can help with recovery. This can be as simple as drinking a glass of water when you get home, or if you want to get scientific about it, drink 16–24 fl. oz. of water for every pound you lost while exercising.

Also, keep in mind that sometimes you need to rehydrate before you pre-hydrate. For example, if you haven’t had any water in a long time, such as after a night of sleeping, you may need to drink some water to rehydrate and then go about pre-hydrating for your activity.

Plan your route: Water weighs a lot (16 fl. oz. is just over a pound), so if you want to avoid carrying extra weight on a run or bike ride, plan a route that will take you by a water fountain where you can drink or refill a bottle. Another option is to use your car like an aid station and plan an outing that does loops from your vehicle. You can stop at your car to refill a water bottle and grab a quick snack.

In the mountains, either carry enough water to get you through the duration of your outing, or bring a water filter and know where a lake or stream is that you can refill from.

Wear sun protection: Getting a sunburn can expedite dehydration, so lather up with sunscreen or wear sun-protection clothing before heading out.

Set a timer: If you tend to lose track of the last time you drank, set a timer on your watch to sound an alarm about every 20 minutes as a reminder to take a sip. 

 

Risks of Improper Hydration

a sweaty biker drinking from the hose of hydration reservoir

Dehydration

Dehydration occurs when the loss of body fluids, usually through sweating, exceeds the amount taken in. Once you've reached the point of feeling thirsty, dehydration has already begun. If you don’t counteract this by drinking water, the body will continue to provide signs that it is running low on fluids:  

Early signs of dehydration:

  • thirst
  • dry mouth
  • decrease in energy

More serious symptoms of dehydration:

  • cramps
  • headaches
  • nausea
  • the “umbles” (stumbling, mumbling, grumbling and fumbling)
  • dark urine with less volume (note that vitamins like B12 can cause urine to be bright yellow, which may not indicate dehydration)
  • decrease in your performance

The remedy for dehydration is simple: Drink water. It’s better to take frequent sips of water rather than chugging larger amounts infrequently. Adding in sport/energy drinks can help restore carbohydrates and electrolytes.

Double-check your water intake by weighing yourself before and after exercise: You should weigh about the same. If you have lost several pounds, then you’re probably not drinking enough water. For every pound lost, drink 16–24 fl. oz. of water and plan to increase your fluid intake next time. With that said, it can be very difficult, if not impossible, to maintain your body weight during intense exercise, especially on a hot day, so don't be surprised if you weigh less.

Overhydration

The flip side to dehydration is overhydration, or hyponatremia. This is a fairly rare condition that mainly affects endurance athletes such as marathon runners, ultrarunners and triathletes.

In hyponatremia, sodium levels in the blood become so diluted that cell function becomes impaired. In very extreme cases, hyponatremia may cause coma and even death.

The symptoms of hyponatremia are similar to dehydration: fatigue, headache and nausea, causing some athletes to mistakenly drink more water and exacerbate the issue.

Preventing overhydration: The key to preventing overhydration is to monitor how much you drink.

  • Don’t overdrink—Stick to drinking about 10 fl. oz. about every 20 minutes and try not to drink more than you sweat. Weight gain during exercise is a telltale sign that you're drinking too much.
  • Add salt—Keep your salt levels balanced by occasionally drinking a sports drink with electrolytes instead of plain water and/or eating a salty snack, such as pretzels. You can also take salt tablets.

 

 

How helpful was this article? Click a star to rate.

47 votes so far - average rating 3.3

Contributing Experts

Megan Stump
Megan Stump

Megan Stump is an REI Outdoor School Instructor in Phoenix, Ariz., and a sales associate at the Paradise Valley REI store. She enjoys hiking, backpacking, climbing, mountaineering and travel.