Why Hydration when Trekking at Altitude Matters Even More

Mountains bring out the best in us, the sense of adventure, the breathtaking vistas, and the quiet moments of clarity are unmatched. But behind all this is an environment that challenges our physiology.

At altitude, air is drier and your respiratory rate increases. As you breathe faster, you lose more water through your breath alone. Add in sweating from physical exertion and there’s an increased risk of dehydration.

Dehydration not only saps your energy but also impairs mental clarity, increases fatigue, and elevates the risk of AMS (altitude sickness) — factors that can quickly turn a great day into a hard one.

Physical Performance and Energy

When climbing, every step requires energy. If you neglect hydration for trekking at altitude, even mild dehydration, as little as 1–2% loss of body weight in water, can impair physical performance. This effect is magnified on long summit days, where endurance and steady effort are key.

According to a comprehensive review published in Frontiers in Sports and Active Living (2024), dehydration reduces blood volume, making your heart work harder to pump oxygen and nutrients to muscles. This leads to faster fatigue and lower work output.

In a study cited in the review, participants who were even slightly dehydrated reported a significantly higher rate of perceived exertion (RPE), meaning they felt the effort was harder than it actually was. For mountaineers, this can slow pace, increase mistakes, and reduce overall safety.

Read the full study here.

Cognitive Function and Decision-Making

Beyond physical strain, dehydration also impairs mental performance, a crucial factor when navigating tricky sections of ridges or making split-second, crucial decisions.

According to the science being well-hydrated can significantly improve brain function. Even mild dehydration (about 1.4% fluid loss) can affect mood, concentration, and working memory, read more about this here. This becomes critical when operating in environments where technical skills can be crucial.

Dehydration can also increase feelings of anxiety and fatigue, creating a cycle that further reduces your focus. On a busy, exposed ridge, this mental fog can make the difference between a safe passage and a mistake on the mountain.

Headache Prevention and Comfort

Many mountaineers blame altitude alone for headaches. While lower oxygen levels certainly play a role, dehydration is a major and preventable contributor.

Adequate hydration can help prevent and reduce headache intensity. Medical studies show that participants who increased water intake reported significant improvement in headache severity and frequency.

For mountaineers, headaches are often the first sign that mild dehydration is tipping into AMS (altitude sickness), and can lead to impaired decision-making. Avoiding Altitude Sickness — Five Top Tips is worth a read if you want to stay ahead of the game. Drinking enough throughout the day can help minimize this risk and keep you feeling clearer and more comfortable above the clouds.

Practical Hydration Strategies on the Mountain

It’s one thing to know hydration is important. It’s another to actually manage it on long days out in the cold, wind, and at altitude.

When planning hydration for trekking at altitude, focus on:

✅ Starting hydrated: Drink well the day before and morning of your climb. Dehydration from the outset is hard to fix later.

✅ Carrying enough and make it accessible: Use bottles that are easily accessible, either in an outside pocket on your rucksack or under the top flap so they are easy to reach.  If you choose to use a hydration bladder, as I do, then make sure it’s not going to freeze – a quick fix for this is to blow the fluid back into the reservoir so it doesn’t freeze in the tube and tuck the mouth piece into your jacket. Make it easy to drink.

✅ Drinking regularly, not just when thirsty: By the time you feel thirsty, you’re likely already dehydrated. Aim for small, steady sips every 20–30 minutes.

✅ Warm fluids for cold conditions: In winter or high altitudes, warm tea or electrolyte mixes can make drinking more appealing and help maintain body temperature.

✅ Balance intake with salts and food: While pure water is essential, consuming it with snacks helps maintain electrolyte balance.

When Hydration Gets Overlooked

On big summit pushes, it’s easy to focus so much on the climb that you forget to drink. You might not feel thirsty due to the cold or excitement, but your body still needs it.

Some climbers report headaches, cramps, and sudden energy crashes, often attributed to altitude or fatigue but actually rooted in dehydration. In severe cases, dehydration contributes to more serious altitude-related illnesses, including AMS.

Being disciplined about hydration can often prevent these “mystery” issues and keep you stronger and safer all the way back to base camp.

Hydration and Long-Term Health

Hydration isn’t just about the immediate climb. Over time, repeated episodes of dehydration can strain your kidneys and cardiovascular system. Staying hydrated supports blood pressure regulation, digestion, and recovery.

Mountaineers often overlook recovery hydration, focusing only on the ascent. Drinking adequately post-climb helps flush metabolic waste, repair muscles, and restore electrolyte balance — making you more ready for the next day’s adventure.

Final Thoughts

Water is your simplest, most essential piece of gear on any mountain. While it doesn’t come with technical specs or shiny marketing, it quietly enables every high step and every clear decision.

I always say to clients: “your harness keeps you safe on the crag. Your water bottle keeps you safe on the mountain”.

So pack it, use it, and plan for it as seriously as you do your helmet or rope.

Your summit success — and safe return — might just depend on hydration for trekking at altitude.