Hydration Guide For Hot Summer Runs

the running mate icon

Let’s start this one out with a story.

On our summer holiday last year I tried to run across the entire island of Elba in the Mediterranean sea. I followed along the GTE (Grande Traversata Elbana), a trail that is around 50k with 3,000+ meters of elevation from the northeastern part of the island to the southwest.

It was summer but temperatures were not that hot. There was no sunshine at the beginning but the forecast showed that the weather would be changing throughout the day. So I had to expect everything from easy rain to a hot burning sun.

So I agreed on some meeting points where my girlfriend waited with the car for me so I could take a short break and refill my water bottles.

At the second to last stop after running for around 30k the sun was burning and the toughest climb was yet to come. I drank a lot of water, ate something and refilled my soft flasks.

Close to the top of the last and toughest climb my girlfriend texted me stating that the road is closed and she couldn’t meet me at the agreed spot. I was running low on water and knew, that I have just a little bit left for the rest that I estimated would be around two more hours of running.

A bit later I took a wrong turn and went one hour in the wrong direction on very technical terrain. So I doubled my two hour estimate! Without any chance to grab water somewhere and not a single human being around, I started to struggle.

The sun came back out and my body sweat out the last bit of fluid. I was down and out, dehydrated, completely out of energy and still had a few miles to go under the burning sun.

I stumbled my way down to the finish and started to get a bit dizzy. This is the closest I got to severe dehydration and I don’t recommend this to happen to anyone!

Obviously I survived but this episode brought proper hydration into focus even more.

So in this post I wanna share some tips on how to proper hydrate especially on hot summer runs. I hope this piece helps you to avoid the situation I was in last summer.

Some Hydration Basics


While probably most runners struggle with dehydration and drinking not enough water, it is in that context always good to mention that also drinking too much water can be a serious issue.

When you drink to much water or sport drinks, you’re blood dilutes and the amount of sodium drops to a sub-normal level. The blood cells swell which can lead to muscle cramps, headaches, vomiting or in severe cases even coma.

The tricky thing is that the symptoms might be similar to dehydration. So it is crucial to know when and how much to drink. Not only in everyday life but especially when you exercise.


Dehydration is generally known for not drinking enough. Dehydration basically means that you have a deficit in total body water.

Of course for us runners that happens when exercising, especially in hot and/or humid conditions. When we sweat a lot and don’t compensate the fluids loss, we get dehydrated.

The symptoms are first of all thirst. Often it’s recommended to drink ahead of thirst and when you feel thirsty it’s already too late. However as mentioned above, try to not drink too much as well.

Other symptoms are a sudden, sometimes massive decrease in performance when exercising. Something you don’t wanna experience especially in a race. Also headache and general discomfort are common signs of dehydration. Ultimately if you experience severe dehydration, your kidneys might fail and things can get really dangerous.

Learn How Much You Need

So as outlined above you can drink both too much and too little water, but for most runners the latter is the bigger, more common issue.

This article would stop here if I could give you a generally valid number on how much you need to drink per hour. But things are obviously a bit more complicated and there are several factors that contribute to the amount of fluids you should take in.

In my own experience I can go for a three hour run in winter without the need of any water at all. In summer, I start suffering after 30 minutes without water.

Of course the temperature and humidity play a major role in your sweating. Remember, sweating is your body’s mechanism too cool itself down. But also workout intensity and your predisposition impact your sweating.

I for example produce a huge amount of sweat compared to others. Therefore my water intake should be above average.

To find out how much you need to drink, there’s a simple thing you can do:

  1. Weigh yourself and note your weight (naked)
  2. Go running for an hour without drinking anything
  3. After you come back wait until you sweat out
  4. Dry yourself and weigh yourself again (naked)

The difference in weight shows you approximately how much fluids you lost. Of course you also shouldn’t take a pee or do anything else that affects your weight in between the two measurements.

Try to do this in several weather conditions and with different intensities (average heart rate) and note the results. After you did this several times, you can extrapolate how much you need to drink when you go running.

This sounds like a lot of work but in the long run it might be worth it! Sure you can just trust your feeling, but with something that can affect your health big time, I would take the safe way.

Invest In Good Hydration Systems

So now that you know more or less how much fluids you need to take in, it’s time to talk about how to carry your water.

There are many different systems on how to carry water by dozens of brands. Basically there are three different categories:

  1. Bottles
  2. Belts
  3. Packs/Vests

With bottles I just mean bottles you hold in your hands and that you can somehow attach to your hands so they don’t fall down if you loosen your grip. I mostly use soft flasks attached to my hands. These go from 2 dl (8.5 floz) up to 5 dl (17 floz).

Then there are belts where small bottles are attached. I don’t use these at all because I don’t want to have some pounds of water attached around my waist. It just doesn’t feel that comfortable when running, especially on trails.

The third option is often the one that can carry the largest amount of water: Hydration packs. My first running pack had a bladder which could hold 1.5 l (50 floz) but there are also smaller and larger ones.

Which brand you go for is obviously a very personal thing and there are tons of reviews around the internet. The important part here is how much water you can carry. Of course you can also use a combination of the options mentioned above.

What To Drink

So you know how much you need for your hot runs and you have the hydration system ready that meets you needs.

But what should you drink? Is water enough?

Well on shorter runs I mostly just use water. However the longer the run, the more I try to use isotonic sports drinks. There are two reasons for that.

First sports drink come with carbohydrates and, in contrast to water, provide some energy. That’s great because on long distance runs the stomach might have difficulties digesting solid foods. So taking in some energy with drinks can help with that.

The second reason is that isotonic drinks have about the same osmotic pressure as your blood. That means that taking in these drinks don’t cause any changes in the volume of your blood cells. Isotonic sports drink are probably the healthiest choice for endurance sports.

But that is not all. On long distances races I also did use Coca Cola on the later stages of the race. This is just for the sugar to take in energy that ends up being available for the body as quick as possible. And again not much solid food to digest here.

If you choose to drink Coca Cola as well, be aware that you might need to shake your bottles and let the gas go. The gas can be difficult for your stomach as well.

Plan Refill Stops

If you go running for several hours in hot temperatures, you might not be able to carry as much water as you need. Or carrying that much wouldn’t be very comfortable. So you need to refill on the way.

And of course it is crucial to plan these refill stops before you head out. Where I live there are two possibilities to refill. Fountains and buying water in a shop.

If you’re like me then running into nature and away from cities is what you love most. But out there in nature it’s hard to get potable water. Even when you run along rivers this water might be polluted.

So plan your route before you start your run and consider when and where you can refill your bottles.

What Else to Carry

Well this is not only the case when it comes to proper hydration but also an advice for all your runs. Especially if you go running for hours and/or into the wild, you should carry these two things with you:

  1. Money
  2. A mobile phone

In case something doesn’t go the way you planned it, money can bring you back home with public transportation or a taxi. Or you can buy food and water along the way.

And the mobile phone can be a life saver. If you get lost, a good map app can get you back on track. Or you can call for help if something happens.


I hope I could shed some light on proper hydration for your summer runs. If you have another approach, feel free to comment below.

Happy running,

We'll never share your email with anyone else.

Leave a Reply

Your email address will not be published. Required fields are marked *