Everybody and Every Body
Before we begin… everybody and every body is different.
These are general guidelines that may work for many people, but they are not a substitute for knowing your own body and what you need before beginning any activity.
With that said, there are a few factors that can change how much water you will need.
Length of Hike
This may affect your water needs the least of all the factors on this list.
If all other factors are equal, how long you are out has less impact than you might think.
Walking a one-mile trail on flat ground with a moderate amount of sweating may not require dramatically more water than walking two or three miles under the same conditions.
That doesn’t mean distance doesn’t matter.
It means distance is only one part of the equation.
Weather
Weather is a tricky one.
Hiking in the heat of summer can feel exhausting. The sweat comes more freely.
However, the colder, drier air of winter can also increase your fluid needs.
Knowing the signs your body is giving you is important in any weather. It can be particularly difficult to judge your hydration needs in cooler or rainy weather because you may not feel as thirsty even while you’re losing fluid.
The rule I like to follow is simple:
Take a drink when you feel the need to pause.
Even if it is only for a few seconds.
Pay attention to your body and the conditions around you.
Difficulty
This one sounds obvious, but it is one that many people miss.
Going from a flat trail to a near-vertical trail is obvious. But what about a slight increase in incline? Or a trail with more climbs than you are used to?
The small increases are where people can get caught off guard.
Know yourself well enough to recognize when an increase in intensity means you will need more water.
But How Much Water?
This is where things get complicated.
There isn’t one number that works for everyone.
How much you need depends on your body, the weather, the terrain, how hard you are working, how much you sweat, and how long you are out.
For me, a useful starting point is about eight ounces of water per hour I expect to be on the trail.
That is a starting point, not a rule.
For some people, that will be too little. For others, it may be more than they need.
For longer or more strenuous hikes, especially in hot conditions, your needs may increase significantly.
I also count water I plan to filter along the way when I know I have a reliable water source and an appropriate treatment method. Not everyone carries a filter, and not every trail has a safe water source. Never assume clear mountain water is safe to drink without treatment.
Ironically, overpacking water can contribute to faster fatigue.
The extra weight is not always worth carrying if you don’t need it.
A liter of water weighs just over two pounds.
Over time and distance, that weight adds up.
The balance between carrying enough water and carrying too much is something every hiker has to learn.
Know yourself.
Know the trail.
Know the conditions.
Then carry what you need.
Water Is Not All You Need
Water is only part of the equation.
When you sweat, you lose more than water. Sweat contains electrolytes, particularly sodium and chloride, along with smaller amounts of other minerals. The amount you lose depends heavily on how much you sweat and how long you are exercising. For shorter, easier hikes, regular food and water may be all you need.
For longer hikes or prolonged sweating, replacing some of those electrolytes can become more important.
That can come from a drink, a snack, or a regular meal.
It doesn’t have to come from a fancy product.
Why Does That Matter?
Let’s take a look at some of the electrolytes your body uses.
Sodium
Sodium helps regulate fluid balance and plays an important role in nerve and muscle function. It is also one of the primary electrolytes lost through sweat.
Potassium
Potassium is important for nerve signals, muscle contraction, and maintaining fluid balance. You can get it from ordinary foods as well as electrolyte products.
Calcium
Calcium is well known for its role in bone health, but it also plays an important role in muscle contraction and nerve function.
Magnesium
Magnesium is involved in many processes in the body, including energy production and normal muscle and nerve function.
The important thing to remember is that hydration is not simply a matter of drinking as much water as possible.
Too little fluid can be a problem.
Too much water can also be a problem.
During prolonged exercise, excessive water intake can contribute to exercise-associated hyponatremia, a potentially serious condition caused by a dangerous imbalance of water and sodium. The old idea that you simply cannot drink too much water is not true.
What’s the Solution?
For most short hikes, the solution is much simpler than the supplement industry would have you believe.
Carry enough water for the hike and conditions.
Bring a snack.
If you are going to be sweating for several hours, consider bringing something that provides electrolytes as well.
There are plenty of electrolyte mixes and drinks available. I have tried several. My favorite is LMNT, but my wife hates it.
To be fair, it is quite salty.
Try different things and discover what works for you.
Once I started paying more attention to electrolytes on longer hikes, I noticed a difference in how I felt approaching a summit. The sluggishness didn’t seem to hit as hard, and while the exhaustion on long climbs didn’t disappear, I found that my legs could go a little longer.
That is my experience.
It may not be yours.
Not every ounce of water you drink needs to contain electrolytes. In fact, for many shorter hikes, plain water and normal food are perfectly reasonable. Electrolyte replacement becomes more relevant as duration, heat, and sweat losses increase.
To Sum It Up
You are the person who knows your body best.
Every “expert” will tell you something different because there isn’t one perfect number for everyone.
My personal rule of thumb is eight ounces per hour.
That’s what I prepare for.
Eight hours on the trail would mean 64 ounces of water.
I might not drink that much every time.
But it gives me a starting point.
The important part isn’t memorizing a number.
It’s paying attention.
Know the trail.
Know the weather.
Know your body.
Carry enough.
Don’t carry so much that your water becomes part of the problem.
And don’t forget to stop every now and then, take a drink, look around, and enjoy the trail.