Dehydration on a high-altitude trek starts before you ever feel thirsty. Dry mountain air pulls moisture out of you without you noticing, and above 4,000 meters that effect multiplies. As a general guideline, most people need 250 to 500 ml of water per hour of hiking in mild weather, and quite a bit more in the heat, at altitude, or on a multi-day expedition. On our trips we schedule hydration breaks every 45 to 60 minutes. It's not a guide's whim: it's the simplest way to avoid the headaches, nausea, and performance dips that later get mistaken for altitude sickness. Drinking too much isn't free either. This guide walks through how much, when, and what to drink, from a one-day hike to an expedition above 6,000 meters.
Key Takeaways
Drink 250 to 500 ml of water per hour of hiking in mild weather, up to 750 ml on hot days, and 0.5 to 1 liter per hour in high mountains above 4,000 m.
Sip 200 to 300 ml every 15 to 20 minutes: chugging a liter at once works less well and overloads your kidneys.
Over a 6 to 8 hour day that adds up to 2 to 3 liters, and on high-altitude expeditions your daily total can climb to 3 to 5 liters, plus electrolytes if you sweat heavily.
Don't wait until you're thirsty: cold and altitude both blunt the thirst reflex, so drink at every break even if you don't feel like it.
Watch the other extreme too: drinking only plain water on long days can dilute your sodium and trigger hyponatremia, which is just as dangerous as dehydration.
These are general ranges for healthy people. If you have a kidney or heart condition, or take medication, check with your doctor before the trip.
How much water should you drink per hour of trekking?
As a general guideline, drink 250 to 500 ml of water per hour of hiking in mild weather, and up to 750 ml per hour on hot days on a ridge or in a canyon. These aren't strict medical figures. They're the practical ranges we use in the field, and they shift with heat, pack weight, and how much you personally sweat.
If you're headed to high mountains or an expedition above 4,000 meters, that reference climbs. Sports nutrition literature on high-altitude activity recommends 0.5 to 0.75 liters per hour as a baseline (Urdampilleta and Martínez-Sanz, 2012), and in practice our guides push that up to 1 liter per hour on the toughest stretches. Effort and altitude stack on top of each other, so the same rule you'd use on a one-day trek doesn't hold up in the high mountains.
The golden rule for spacing it out: sip 200 to 300 ml every 15 to 20 minutes rather than a few big gulps. Chugging a liter once you're already dehydrated doesn't work as well, it overloads your kidneys, and it sends you looking for a bathroom at the worst possible moments on a long trek.
Over a 6 to 8 hour day, those numbers usually add up to 2 to 3 liters of water alone, not counting mate or food. It helps to split the load across two bottles or a hydration bladder you can reach without taking off your whole pack. Further down we'll cover how to read your urine color and body weight to check if you're on track.
How much water do you need per day on a high-altitude expedition?
Above 2,400 meters, add 1 to 2 liters a day to your usual intake. In high mountains (above 4,000 m), the daily reference total climbs to 3 to 5 liters, counting water, mate, soups, and electrolyte drinks.
That number drops in extreme situations: on very demanding expeditions, 3 liters a day works fine. A handy rule of thumb: 1 liter of fluid for every 1,000 meters above sea level. At 5,000 m, aim for 5 liters.
This table sums up the reference ranges by altitude, useful if you're planning a long or high-altitude expedition.
| Altitude | Liters per day (reference) | Notes |
|---|---|---|
| 2,400 to 4,000 m | Usual intake + 1 to 2 liters | Add electrolytes if you sweat heavily |
| Above 4,000 m | 3 to 5 liters | Counting water, soup, mate, and sports drinks |
| Demanding expedition | 3 liters | Floor of the range above under extreme effort, not the norm |
On top of that, there's a pre-hydration strategy that's easy to overlook: start drinking water with electrolytes 24 hours before you set out, and add 500 to 750 ml of an electrolyte solution about 2 hours before you're fully exposed to altitude (Liquid I.V., 2024). Arriving well hydrated at the foot of the mountain buys you margin for the first, hardest days of acclimatization.
Why do you need to drink more water at altitude?
Because at altitude your body loses fluid through channels you can't see. Mountain air is much drier than at sea level, and warming and humidifying it before it reaches your lungs means you exhale far more moisture than usual. A 2023 study of mountain soldiers based in Mendoza measured that loss at up to 1,900 ml a day in men and 850 ml a day in women at altitudes up to 4,000 meters (DIAETA, 2023).
On top of that, you urinate more. Your body compensates for lower oxygen by urinating more during the first days of acclimatization, and cold adds its own diuretic effect on top of that. Several leaks are happening at once, and thirst alone can't keep up.
These losses aren't just an inconvenience. Dehydration disrupts your fluid and electrolyte balance and your body's ability to regulate its temperature, and if a climb runs long, that adds to the risk of frostbite from the intense cold above 4,500 meters (Urdampilleta and Martínez-Sanz, 2012). One more reason not to reach nightfall already behind on fluids.
Add in the cold, which dulls your sense of thirst, and the altitude, which kills your appetite. Plenty of people stop drinking right when they need it most. Gradual acclimatization helps, but it doesn't replace the habit of drinking constantly.
Hydration alone doesn't cure or prevent acute mountain sickness, but dehydration makes almost all of its symptoms worse and harder to read. For more on that, check our guides on how to prevent altitude sickness and what happens to your body during acclimatization.
Is water enough, or do you need electrolytes too?
Plain water isn't always enough on long days, because sweating costs you sodium and potassium (it's why shirts end up with those white sweat stains), and drinking only water can dilute what's left of those salts even further. On a short outing of a few hours, water alone is fine. On a full day of effort or serious heat, it's worth alternating.
The idea is simple: alternate water with a sports drink or rehydration salts in moderate doses, following the label. Not every sip needs electrolytes, and you shouldn't overdo it either. The goal is to replace what you lose, not to flood your system. If you have high blood pressure or a medically prescribed sodium restriction, that's worth discussing with your doctor before the trip.
If you like precision, sports science gets fairly specific here. During the hike, look for an isotonic drink with 6% to 7% fast-absorbing carbohydrates and 0.5 to 0.7 grams of sodium per liter, served cool (10 to 15°C) for better absorption. Once you reach camp, your recovery drink can be more concentrated: 8% to 10% carbohydrates and 0.7 to 1.1 g of sodium per liter (Urdampilleta and Martínez-Sanz, 2012), with a 4-to-1 ratio of carbs to protein if you add protein.
Don't overdo the recovery dose: for every gram of glycogen your muscles store, your body holds onto about 3 extra grams of water (Lizama Castroviejo, University of Zaragoza, 2025), so this intake needs to be measured, not improvised.
On our high-mountain trips, we push this at every scheduled stop, because it's where we most often see people who trained hard but slack off on hydration. Water and electrolytes weigh almost nothing, and they're what keeps a great day from falling apart in the last few hours. But watch out: the opposite mistake, drinking too much without salts, has a name too, and it's just as dangerous. More on that next.
Can you drink too much water? The risk of hyponatremia
Yes, it's possible. Sweating and exertion cost you mineral salts, mainly sodium, and if you only replace them with plain water (or cups of tea or coffee), you dilute what sodium you have left even further. That's called hyponatremia: a serious electrolyte disorder, well documented in mountain medicine literature, that causes headaches, nausea, and confusion, and in extreme cases can be life-threatening (Urdampilleta and Martínez-Sanz, 2012).
Sodium is the single most important mineral for holding fluid in your body and keeping your nerves firing properly, so this isn't a minor detail. It's also why we push electrolyte juice mixes and not just plain water on long days.
There's an even more confusing overlap with acute mountain sickness (AMS). Some people with AMS retain fluid abnormally and their hands or face swell up. In that case, drinking more plain water doesn't help at all, and can make things worse if it isn't paired with the right dose of salts. If you notice swelling along with a headache at altitude, tell your guide: it could be AMS, not simple dehydration.
What are the warning signs of dehydration in the mountains?
The first signs are noticeable thirst, dark and scarce urine, a headache that doesn't ease with water, and fatigue that doesn't match the effort. If these show up, it's not time to push the pace. It's time to stop, drink, and check on the group. This table helps you read the progression.
| Level | What you'll notice | What to do |
|---|---|---|
| Mild | Thirst, dry mouth, dark yellow urine | Sip water and add electrolytes |
| Moderate | Headache, dizziness on standing, unusual fatigue, cramps | Stop, rehydrate with salts, rest in the shade |
| Severe | No urination all day, confusion, loss of skin elasticity | Stop the activity and seek medical help |
If you're heading into the mountains without a guide, this is a red flag worth knowing: if someone in your group hasn't urinated all day, speak up and get help right away. It's one of the clearest signs something is wrong, and the sooner it's caught, the easier it is to fix with rest and fluids.
Two simple checks let you get ahead of the table above. The first is urine color at every stop: clear to pale means you're well hydrated (euhydration), dark yellow is the clearest sign you've fallen behind. The second is body weight: tracked before and after a long day, a loss of more than 2% of your body weight from fluids already hurts your performance and endurance (DIAETA, 2023), well before you feel any severe symptoms. Actually weighing yourself out on the trail is close to impossible in practice, but the effect itself is well documented in the research.
How do you make sure you have safe water on the trail?
By always carrying a way to purify water and never trusting a questionable source. On expeditions we carry purification tablets, because getting sick at altitude dehydrates you even faster.
At high-altitude camps (between 5,000 and 6,000 meters), melting snow is often the only water source available, and that water has zero minerals in it: no sodium, magnesium, or calcium. Purifying it isn't enough there. It needs salts and carbohydrates added, because drinking it plain speeds up dehydration and exposes you to the hyponatremia we mentioned earlier (Urdampilleta and Martínez-Sanz, 2012).
Water availability at mountain huts varies by season and location, so always ask before drinking from a hose or a shared tank. If you're planning to hike Cerro Champaquí on your own, don't assume you'll find drinkable water along the way. Plan how much you're carrying from the bottom.
The same goes for the high mountains of Mendoza. If you're planning your first serious expedition, ask us about our Mendoza destinations and our upcoming trip dates so you arrive with your hydration plan sorted instead of improvising on the trail.
How do you manage your hydration in extreme cold?
On summit pushes like those on Aconcagua, with temperatures of -20 to -30°C, the main challenge stops being how much to drink and becomes keeping your water from freezing. Hydration bladders (camelbacks) worn on your back freeze fast in those conditions. Past 5,000 m they're not a great choice even in normal conditions, and in winter that drops to 4,000 m. If it's all you have, carry it up front, inside your jacket and against your chest, with the tube wrapped in some kind of insulation. But insulated bottle covers are really the better option for keeping water from freezing in the first place.
For hot drinks, a thermos of salted soup (providing 0.7 to 1.0 g of sodium per liter) works better than tea or coffee in large doses. Caffeine above 200 mg has a diuretic effect that speeds up exactly what you're trying to avoid, so in freezing conditions, soup wins.
During rest breaks, don't overdo very salty food: it raises blood pressure and can lead to either dehydration or fluid retention, neither of which helps at altitude.
Frequently asked questions about hydration at altitude
How much water should you drink per day on a high-altitude trek?
As a general guideline, 2 to 3 liters over a 6 to 8 hour day at moderate altitude, and up to 3 to 5 liters a day on an expedition above 4,000 meters. This is a general range for healthy people: adjust it to your own sweat rate and check with a doctor if you have a medical condition.
Does chugging water help if you forgot to hydrate?
Not as much. Your body absorbs steady sips throughout the day better than one big gulp once you're already dehydrated. If you fell behind, catch up gradually and add electrolytes instead of just water.
Are electrolytes mandatory on every trip?
No, but they're recommended. On short outings of a few hours, water is usually enough. On long days, in heavy heat, or with heavy sweating, alternate water with salts or a sports drink in moderate doses to replace sodium and potassium. Powdered juice packets tend to work well for this.
Is dehydration the same thing as altitude sickness?
No, but they look alike and feed off each other. Dehydration causes headaches, nausea, and fatigue, symptoms that also show up in acute mountain sickness. Being well hydrated doesn't prevent AMS on its own, but it helps keep the symptoms milder and easier to read.
Is it dangerous to drink only water, with no salts, on a long trip?
Not automatically, but it can be. Without sodium in the mix, too much water dilutes your blood and can cause hyponatremia, a condition that causes headaches, nausea, and confusion, similar to dehydration but from the opposite cause. Ideally, on long days you'd alternate water with electrolytes in moderate doses.
How do you keep your water from freezing on a high-altitude expedition?
Carry your bottles insulated, with at least one inside your jacket and against your body. Keep the rest in your pack, ideally wrapped in something protective too. On cold summit pushes, a thermos of soup, tea, or hot mate is more reliable than counting on bottles of liquid that's already gone cold.
Can you trust water from streams and mountain huts?
Not always. It depends on the area, nearby animals, and the specific water source. It's best to always carry purification tablets and treat water from natural sources whenever you're unsure it's safe. At mountain huts, ask about water quality before drinking, since availability and quality change with the season.
If you're planning your first expedition above 4,000 meters, set up a call with Mons on WhatsApp at +54 9 3512 11-3842. We'll walk you through the hydration plan we use, tailored to whatever trip you have in mind, whether it's a weekend in Córdoba or a multi-week expedition.