Women hiking near water

How Much Water Should You Drink on a Hike and Why?

Stream in the Catskill
Stream in the Catskill

Fluid replacement is critical to athletic performance. Yes, I said it, athletic. That’s what extended hiking is. I’m not talking about your walk in the local park, but intensive hikes that last longer than 1.5+ hours. I hear many theories on how much water one should drink during sporting events and many are “one size fits all” in nature.

Intense activities lasting longer than an hour will require a specific re-hydration strategy. This applies to both hot and cold environments. It is unclear of the beneficial effect of re-hydrating for activities lasting less than 45 minutes, especially if you begin hydrated.

When hydration bladders first came out, like many people, I ran out and got one. I mean, really, the thought of not having to take my pack off to get at the water was too good. I see people I hike with using these bladders like IVs. Almost never taking them out of their mouth. Constantly sucking water. But since the time I bought mine I’ve reconsidered the use of this as a hydration solution. If you read on I’ll tell you why and what the science is telling us about hydration.

Dehydration makes you clumsy and stupid

Being clumsy and stupid is not the way to be in the back-country.

A water loss equivalent to 2% or more of body mass appears to reduce endurance-exercise performance in both temperate and hot environments, especially when the duration of exercise is around 90 min or more (1).

Research on high-level soccer players has shown as little as 2.4% body mass loss is associated with a 5% loss in skills performance. In other studies, dehydration was associated with a reduction in power output, speed, and running times (2). It must also be noted that low levels of dehydration impact cognitive function and mood (1). Not re-hydrating can make you mentally / physically slow and cranky.

Why hydrate?

Well, it’s fairly simple. Dehydration can reduce performance and increase the risk of heat and cold-related illness. Even in the absence of heat or cold illness, you can experience, simple dry mouth or more seriously, weakness/fatigue, dizziness, headaches, poor sleep, constipation, and palpitations (feeling that the heart is jumping or pounding). So staying hydrated keeps you moving and healthy.

However, remember this, excessive over-drinking should be avoided because it can also compromise physical performance and health. In rare cases, people who drink too much water may reduce blood sodium levels and experience a condition known as hyponatremia (see symptoms here), or in hiking, exercise-associated hyponatremia (EAH), which can be fatal or simply feeling bad in sub-clinical states.

How much to drink?

This is a bit tricky. You’ll need to consider several factors such as age, gender, body size,  weather/climate, duration of your outing, the weight being carried, the speed of travel, terrain, fitness, acclimatization, and foods you are eating (dehydrated foods have little or no water where fresh fruits have lots). Keeping the above in mind will give you a general idea of how often you should be drinking on a given outing and if you need to mix in a sports drink.

New guidelines?

New guidelines (2015) published in the Clinical Journal of Sport Medicine recommends drinking when thirsty (4). The guidelines specifically say:

 “Given that excessive fluid consumption is a primary etiologic factor in EAH, using the innate thirst mechanism to guide fluid consumption is a strategy that should limit drinking in excess and developing hyponatremia while providing sufficient fluid to prevent excessive dehydration”.

In other words, using your body’s natural system of thirst recognition to guide you. However, remember thirst is subjective and the symptoms of EAH are somewhat similar to dehydration.

In this writer’s opinion, it may not “hold water” in cold environments where thirst perception is altered and one can lose 3 – 8% of body mass quickly (4).  In cold environments, urine color may be a better indicator than thirst, but these are my own thoughts. Additionally, at altitude or in very hot and humid conditions over time this may be problematic. (5) Be cautious.

I have to admit, that I have been using “thirst” as an indicator for years. While others are gulping water at breaks or sucking from hydration packs, I only drink when the early hints of thirst hit. I have never had a problem with dehydration. But I have also observed many people dehydrate on the trail due to “forgetting” to drink.

It could be that I have been hiking for so long that I have simply figured out my hydration schedule and it has nothing to do with my “sense of thirst”.

So what to do?

  1. A common recommendation includes hydrating before hiking. Drinking at least 4 hours before exercise consuming 5-7 ml of fluid per kg of body weight. Also slowly consuming 3-5 ml of fluid per kg of body weight about 2 hours before leading up to your hike. Start your hike hydrated.
  2. Become an expert regarding your body. Know the very early signs of your own thirst. Remember, it’s subjective to a point.
  3. Get an idea of how often you should drink based on your physiology. You can follow the link below for an interesting way to tell if you are hydrating enough during exercise. This article has some good information on how to gauge the amount of water you’ll need during exercise. Use this to determine how often you need to drink.
  4. Bring foods that contain a higher water content. Fruits are good food/water sources. Foods with water will absorb slower but provide other nutrients.
  5. Use performance drinks to help replace lost electrolytes and for longer outings greater than 60-90 minutes add a 6-8% carbohydrate solution to maintain blood glucose levels. Even though fluid replacement needs vary, generally 3 to 8 oz every 10 – 20 minutes is recommended.
  6. Know your trip and weather conditions, cool vs. hot/humid matters.
  7. Keep an eye on your pee. If it is starting to look like apple juice (it should be almost clear or look like lemonade), drink-up!
  8. Assess your trip route and figure out how much water you need to have at any one time. You may be able to refill along the way which means carrying less weight.
  9. Never ignore thirst.
  10. Rehydrate after your trip. The goal after an intense hike is to replenish lost fluid. An individual must consume 150% of lost body weight in 6 hours after intense exercise to achieve normal hydration. Therefore the recommendation is for every pound of body weight lost consume 20-24 oz of fluid. To replenish lost electrolytes use a sports drink.  For rehydration purposes, avoid alcoholic beverages.

The amount of water you should carry depends on your trip. If you are going to be near dependable water sources for much of your trip you may be able to travel with one 1 liter bottle filled and resupply with a filter or other quick purification method when needed. Carrying less water means carrying less weight. But if your water supplies are suspect (meaning dry) carry more water. Always err on the safe side.

Sawyer MINI works well with the SmartWater Bottles
Sawyer MINI works well with the SmartWater Bottles Scott L. | copyright Challenged Hiking

You can save weight by ditching the Nalgene type bottles in favor of a simple 1-liter spring water bottle. Another option is using a filter/drinking system like the Sawyer Mini Water Filter which acts as a filter and hydration bladder system.

Healthy water

Unless you carry all the water you need, which you can do on short hikes, you’ll want a way to keep your water resupply safe. I have to admit, I drink from high mountain streams. Hot and tired I take a handful. But nothing more.

There are a lot of reasons why people get sick in the backwoods and most of it is probably due to poor hygiene in camp or on the trail. Yes, they pee or poo and do not “wash”. Heck, I see 50% of men in public toilets not washing, gross. In the back-country, this is something that a simple antibacterial wipe could prevent, so carry a few. Having said this, all water should be suspect, some more than others.

The simple rule of thumb is: Treat and/or filter your water. There are many ways to do this from tablets, filters, boiling, and even UVGI sterilization. But that’s another post.



1. Maughan, Ronald J., and Susan M. Shirreffs. “Development of individual hydration strategies for athletes.” International journal of sport nutrition 18.5 (2008): 457.

2. Casa, Douglas J., et al. “11 Hydration for High-Level Athletes.” Nutrition for Elite Athletes (2015): 249.

3. “Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference.” LWW. Clinical Journal of Sport Medicine:, July 2015. Web. 22 Oct. 2015. <http://journals.lww.com/cjsportsmed/Fulltext/2015/07000/Statement_of_the_Third_International.2.aspx>.

4. “Cold Weather Increases Risk Of Dehydration.” Cold Weather Increases Risk Of Dehydration. UNH Media Relations, 28 Jan. 2005. Web. 22 Oct. 2015. <http://www.unh.edu/news/news_releases/2005/january/sk_050128cold.html>.

5. Shilton, AC. “The New Rules of Hydration.” Outside Online. Outside Magazine, 17 Jan. 2017. Web. 22 Jan. 2017.