How Much Water to Bring on a Hike

Water is the heaviest thing in most daypacks, which makes it tempting to carry less.

But running dry on a hot climb is miserable at best and dangerous at worst,

while hauling far more than you need wears you out for no reason.

There is no single right amount for every hiker.

The good news is that a simple starting rule, adjusted for the conditions and for your own body, gets most people close.

Here is how to work out your number.

A Simple Starting Point

A common rule of thumb is to plan for about half a liter of water (roughly 17 fluid ounces) per hour of hiking in moderate temperatures at a moderate effort.

For a four-hour hike on a mild day, that works out to around 2 liters.

Treat that figure as a baseline, not a limit.

Add a reserve for delays, since hikes often take longer than planned, and increase it for heat, steep climbs or a heavy pack.

On short, cool, shady walks, you may drink less.

Here is how the adjustments might stack up.

For a five-hour hike on a hot day with a big climb, the baseline suggests about 2.5 liters.

Add extra for the heat and the climbing, then a reserve,

and you may want to carry 3.5 liters or more,

or plan a refill at a reliable source along the way.

Start the day well hydrated too.

Drinking a glass or two of water with breakfast means you begin the hike topped up instead of playing catch-up on the first climb.

What Changes How Much You Need

Your water needs can vary widely from one hike to the next. The biggest factors are:

• Heat and sun: Hot, exposed trails make you sweat far more than a cool forest walk.
• Humidity: Sweat evaporates poorly in humid air, so you sweat more while cooling less.
• Effort: Steep climbing, a fast pace and a heavy pack all raise your sweat rate.
• Altitude: At higher elevations you lose more moisture through breathing, and thirst may be less noticeable.
• Cold, dry air: Winter air is often very dry, and cold can dull your sense of thirst, so dehydration sneaks up on you.
• Your body: Size, fitness, acclimatization and individual sweat rate all make a difference.

Find Your Personal Number

The best way to refine the rule of thumb is to learn your own sweat rate.

After a few hikes, you will know whether you are a light or heavy sweater and how much you actually drink.

One simple method is borrowed from endurance sports.

Weigh yourself before and after a short hike in typical conditions, and note how much you drank along the way.

Every pound you lose is roughly a pint of fluid, and every kilogram roughly a liter,

so add that to what you drank and divide by the hours on the trail to estimate your hourly sweat loss.

Keep notes after each hike: the temperature, the distance and climbing, how much you carried and how much was left at the end.

Over a season, those notes become a reliable guide for your own trips.

Plan Your Refills Before You Go

You do not always have to carry all your water from the start. If the route passes reliable streams,

lakes or springs, you can carry less and refill along the way, as long as you can treat the water.

Research sources carefully. Check recent trip reports and ask the land manager or a ranger station,

because seasonal creeks and springs can dry up in late summer or during droughts.

Mark sources on your map and carry enough to reach the next one with a margin to spare,

in case it turns out to be dry.

At a reliable source, drink your fill before you leave, then top off your bottles.

Starting each stretch well hydrated means you need to carry a little less.

Treat Water From Natural Sources

Even crystal-clear mountain water can carry bacteria, parasites and viruses that cause illness.

Unless water comes from a tested, treated supply, treat it before drinking. Common methods include:

• Filtering: Pump, squeeze and gravity filters remove many contaminants as you refill.
• Chemical treatment: Tablets or drops are light and compact but need a waiting period before the water is safe to drink.
• Boiling: Bringing water to a rolling boil for 1 minute (3 minutes above 6,500 feet) is very effective but needs a stove, fuel and time.

Not every method protects against every type of germ, so check what yours covers and follow the manufacturer's instructions, including contact times.

Collect from flowing water where possible, let silty water settle or strain it through a cloth first,

and keep untreated water away from your drinking bottles and mouth.

Carry It Comfortably

Water is heavy, since a liter weighs about a kilogram (roughly 2.2 pounds).

Carry it close to your back in the middle of your pack or in a hydration reservoir,

and use side pockets for bottles you want to reach while walking.

Reservoirs with a drinking tube make it easy to sip often, which helps many hikers drink more steadily.

Bottles make it easier to see how much you have left and to refill at a source.

Many hikers use both: a reservoir for sipping and a bottle as a visible reserve or for mixing electrolytes.

Whatever you carry, check your supply at every break.

If you have used more than half your water before reaching your turnaround point, head back or adjust the plan before you run short.

Signs You Are Drinking Too Little or Too Much

Thirst, dark yellow urine, headache, fatigue, dizziness and muscle cramps can all signal that you are falling behind on fluids.

Drink small amounts regularly, and rest in the shade if you start to feel unwell.

Drinking too much plain water can also cause problems.

On long, hot hikes, large volumes of water without enough salt can dilute the sodium in your blood, a condition called hyponatremia.

Warning signs include nausea, headache, confusion and swelling of the hands or feet.

Balance water with salty snacks or electrolyte drinks, and seek medical help if someone becomes confused or seriously unwell.

Frequently Asked Questions

Should I drink before I feel thirsty?

On most hikes, sipping regularly and letting thirst guide you works well.

In hot weather or at altitude, drink at every break as a habit, since you may not notice how much you are losing.

Do I need electrolyte drinks?

For short, cool hikes, water and a normal snack are usually enough.

On long, hot or very sweaty days, electrolyte drinks or salty foods help replace the salt you lose.

Is it safe to drink from a stream if the water looks clean?

Clear water can still contain germs you cannot see.

Treat all natural water unless you know the source is safe, and bring enough treated water to reach the next reliable refill.

The Takeaway

Start with about half a liter per hour in moderate conditions, then adjust for heat, effort, altitude and your own body.

Plan refills carefully, treat natural water, carry a reserve, and balance fluids with salt on long days.

With a little attention, you will always have enough to finish strong.