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How To Carry Water When Running: Using Soft Flasks (Water Bottles) and Hydration Bladders

When going on long runs, and especially trail runs and running in hot climates, it’s important to be able to comfortably carry your own water with you rather than relying on either not needing any water or that you will be able to use a safe water source along the way. Even if you have run a route previously and there was a nice, clean water fountain en-route, that isn’t to say that it won’t be less clean, or out of order, when you next run past it, so it’s best to be self-sufficient and at least carry a minimal amount of water that you expect to need for your run. There are different ways to carry water when running, the two most popular with trail runners being to use a hydration bladder or to start using soft flasks, which are soft, collapsible water bottles that you can carry with you easily.

When to comes to choosing which is the best way to carry water for you personally, you can either use one of these options or a combination of both a hydration bladder and water bottles. This post covers the pros and cons of hydration bladders and soft flasks for carrying water with you when running, to help you decide which method will work best for you.

How to carry water when running – Table of Contents

Pros and cons of hydration bladders for carrying water running

Nathan VaporSwiftra Womens Hydration Pack Best hydration packs for women trail and kale 1

Advantages of using a hydration bladder in your running pack

  • A hydration bladder can help balance out the contents of your other gear in your running pack, by storing the water (which is heavy) in the rear of the pack, freeing up space in the front pockets for other essentials such as nutrition and a phone
  • It is a neat solution to drinking while running, as hydration bladders come with a hose and mouthpiece that you can clip close to your mouth to easily take sips while running or hiking
  • Some people find carrying water bottles on the front of their body is uncomfortable. Carrying your water on your back can be a great option if that sounds like you.

Downsides to using a hydration bladder to carry water running

  • You can’t see how much you have left – so you risk running out or getting low on water when you don’t expect it
  • If you have a smaller hydration pack then the bladder, at least when full, may occupy the majority of that space, leaving little room for gear in the back of your pack
  • The water tends to warm up more quickly as it is up against your back and usually in more sunlight than the front of your body
  • It can be a pain to refill a water bladder mid-run (for example, during a long trail race). It may mean that the rest of your gear needs to be taken out (and possibly forgotten to put back) in order to do so.
  • if you’re just using the hydration bladder and no other container, you can only have one drink, i.e. water, whereas having two bottles means you can have one full of water and use the other for electrolyte drinks, for example.

Pros and cons of soft flasks for carrying water running

Advantages of using soft flasks for carrying water running

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  • Soft flasks do not slosh (very much) as the soft sides collapse in to eliminate air spaces, and when the volume of liquid is reduced
  • When they get emptier, they condense and take up less space
  • You can carry two bottles and have different drinks in each
  • You can easily monitor how much water you have left and whether you will need to refill them soon, or conserve water to last to the end of your run

Downsides to using soft flasks for running

  • Soft flasks can be difficult to clean if they have a narrow neck opening
  • When using soft flasks this puts a lot of weight (the water within them) in the front of your hydration pack
  • Electrolyte and other running hydration powders and flavored drinks can stain or add a taste to the bottle that is difficult to remove, even after washing them out a few times.

Other ways to carry water when running

Hard water bottles such as bike bottles

If you’re starting out running and do not have a hydration bladder or soft flasks then any water bottle with water in it is better than taking no water with you, which I don’t recommend especially if you’re trail running, going on a long run, or running somewhere hot (even if it’s only intended to be a short run).

However, it can be annoying carrying a hard-sided, sloshing water bottle with you on your run, so you will probably find yourself looking for other ways to carry water when running pretty quickly!

Running waist packs / fanny packs

If you do not like the idea of wearing a hydration pack for running then you can get running waist packs / fanny packs that are designed to carry water bottles.

In our experience, these waist packs can be great for shorter runs, and especially road runs, however many people find that it is more comfortable to carry gear in a backpack than in a waist pack, but this is an option out there if you have a strong preference for doing so.

Where to buy running hydration bladders and soft flasks

If you are looking for a new way to carry water when running, and do not already own a running hydration pack, consider making an investment in your running gear by buying yourself one – they last for years and will likely encourage you to run more by making it much easier to carry what you need with you.

Running hydration packs are typically sold either one or two water bottles, or a hydration bladder included, so this is another great reason to buy one.

To visit our hydration pack gear guides, which include details of the brands and styles of men’s and women’s hydration packs which we rate highly for trail and ultrarunning in particular, click the buttons below

It’s also worth noting that if your chosen running hydration pack comes with a bladder, that doesn’t mean to say that you can’t use it with bottles instead (or as well) – and vice-versa – but it pays to buy a hydration pack or pair of bottles from the same brand as your hydration pack, to ensure they fit in the pockets of your pack.

One of Trail & Kale's co-founders, a mom, and guardian of our resident trail dog, Kepler, Helen can be found trail running with Kepler and enjoying road runs with her mini in a jogging stroller, all while testing out the latest running gear for our readers.


  1. I find the UD bottles quite hard to use – hard to use the click valve, hard to get in and out to refill, floppy and try to escape. I want to replace – do you know if the salomon bottles will fit in the UD vest?

    • Hi Charlotte, I would say it depends on the style of your vest, the older UD vests have small bottle pockets but the newer ones should fit a Salomon bottle. When I tried it I had to avoid filling the Salomon bottles completely as they’re longer and narrower than the UD equivalent, this way I could stuff them in the pockets and secure the pocket bungee tightly to stop them bouncing out.

  2. I purchased 2 of the newer UD body bottle IIs. The very first time I used them one developed a crack in the material and the other one appears to be getting one also. The material is much thicker than older bottles and hole is right where bottle folds so I can see the issue. Do you have a suggestion for a better replacement? I’ve contacted UD but as of yet gotten no response. Any advice would be greatly appreciated. Dave

  3. Does anybody have any tips for keeping the bottles from falling out. I used my salomon once and the bottles kept on jumping out of the pockets.

    • Hi Tom, are you also using a Salomon race vest or another brand? If it’s another brand then sometimes it doesn’t work that well to mix and match the bottles and vests due to different width/length bottles and pockets… If it is a Salomon one, then I suggest ensuring the bottles do not have any air in them (which will help them be as small as possible) and that you stuff them right down into the pockets so the plastic caps are tucked in the pockets as well as the bottle. It can be quite snug but sucking the air out beforehand should help you get them all the way in so they don’t work their way out again. I hope that helps!

  4. One thing not mentioned is what a pain it is to put soft flask bottles back into the vest pocket. This is what I hear most ultra runners complain about regarding the soft flask bottle. I understand there are advantages and disadvantages to both the hard and soft bottle, I just wish the companies who sell hydration vests would provide an option to purchase the vest with a hard or soft flask bottle that actually fit the vest they were selling.


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