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Are there any tricks to estimate the amount of remaining water in a hydration bladder without pulling it out of the rucksack? Pulling it out is hard and cumbersome with all my rucksacks. In addition, my Deuter Streamer 3.0 bladder doesn’t even have markings (I could add those with permanent marker).

The uncertainty about remaining water makes me reluctant to drink. Often I try to consciously preserve water, only to have a whole liter remaining when I get down from a mountain.

I thought about weighing the whole rucksack with a fishing scale, but then you still have to take the rucksack off and carry a scale with you. You’d also have to account for all items you’ve taken out of the rucksack (e.g. snacks, jacket).

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  • Can you fit your hand into the compartment with the bladder? I can on my little cycling backpack, unless it's stuffed with clothes, but couldn't on another pack with anything else in there
    – Chris H
    Jan 3 at 18:08
  • There's a long list of disadvantages of bladders, and I don't see any advantage whatsoever over a bottle.
    – user2169
    Jan 3 at 22:35
  • @BenCrowell: I don’t want to start a discussion, but the main advantage of hydration bladders is that you can drink while walking/climbing/running. Their shape and flexibility also makes packing easier and they lose volume as you consume the content.
    – Michael
    Jan 4 at 8:40
  • As csk noted in his answer, this advantage is void if you restrict your drinking because one cannot accurately gauge the remaining water. For climbing I now prefer to simply attach a bottle to the harness using a carabiner. It is easily available at the belay without the need to take of the backpack (and potentially drop it).
    – Manziel
    Jan 4 at 9:07
  • 1
    Not a direct answer to the question, but you shouldn't ration water for fear of running out: outdoors.stackexchange.com/questions/6875/…. You're better off drinking the water than saving it. Jan 4 at 13:02
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This is a known downside with water bladders. In my opinion it's the largest downside of a water bladder compared to a water bottle. You don't know you're running low on water until you're completely out, and even then it's hard to tell if you're actually out of water or if you just got a kink in the hose.

The main benefit of a water bladder is that the easy, hands-free drinking makes it easier to stay well hydrated. If uncertainty over how much water you have left is stopping you from staying well hydrated, you're missing out on the main benefit of using a water bladder.

The solution is having more than one water container. That way when you run out of water in your water bladder, you have more water. There are two basic ways to do this:

  • Carry a full water bladder as your main water supply, and have a small "backup" or "reserve" of water in a bottle. Drink freely from your bladder without fear of running completely out of water, because you know there's always a little bit left after you do. If you do run out of water from the bladder and you're not almost done with your hike, that's the time to start drinking conservatively. But you don't need to conserve too much, because having to stop and drink from a water bottle will naturally reduce how much you drink.

  • Carry two water bladders, with half your supply in each bladder. Both bladders can go in the same water bladder pouch. You can run one drinking tube out of either side of your pack to start with, or you can keep the top of one tube inside your pack and swap them when the first bladder runs dry. If you're trying to keep pack weight minimal and don't mind a bit of inconvenient fiddling around, use one drinking tube and switch it between bladders. When you run out of water in the first one, you know you're halfway through your supply. If you're not at least halfway through your hike at that point, drink a bit less frequently. If you get to the halfway point in your hike without finishing your first water bladder, you can drink more frequently than you have been.


A few useful tips that came up in the comments section:

A water bottle can be more convenient to drink from during rest breaks, when you're not wearing your pack.

If you drink your bottle dry during a break, you can refill it from the hose of the water bladder. It helps if the pack is higher than the bottle (eg, if you're wearing the pack, hold the bottle down near your waist).

You can get an inexpensive, lightweight bottle in just about any size by reusing a drink bottle. For a 1L of 750mL size, I like sport drink bottles (eg, Gatorade or Powerade) or Smart Water bottles. Sport drink bottles are relatively sturdy because the bottles have ridges for reinforcement. Smart Water bottles are an unusual shape, tall and skinny, which may be useful for fitting them into a small water bottle pouch; I also find the drinking tops very easy to drink from, but the flip tops do tend to break after a while. Single-serve soda bottles are not as durable, but they're widely available and easily replaced when they get damaged. For a mini bottle (~250mL), look for children's drinks or juice, or small soda bottles.

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  • 2
    I love the second idea. The first is what I usually do, but for other reasons: I hate needing to use a bladder during rests and for cooking. The backup bottle solves that, and can be refilled quickly. Jan 4 at 16:03
  • 1
    200-250ml bottles are good for reserves if you don't want a full-size one. The ones containing some kids' drinks are dturdy enough to rinse and refill. If you're going to switch the same tube between bladders, you either need self-sealing hose ports on the bladders or a plug for the spare - I have neither but mine are cheap
    – Chris H
    Jan 4 at 16:32
  • @ChrisH Good point. I didn't realize there were water bladders that aren't sealed when the hose is detached, but I'm still using the 3L Platypus that was my first water bladder.
    – csk
    Jan 4 at 18:55
  • Another reason to bring standard bottles as well, in my experience, is that bladders are much more fragile, i.e., easy to puncture when refilling or due to handling wear.
    – Reid
    Jan 4 at 21:01
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The few times I have cared how much I have left I could get a decent feel for it by running my hand between the bladder and the partition that separates the bladder from the rest of the pack. It's not real accurate but it's always been enough to answer the question of whether it's safe to give away my backup bottle.

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First I want to mention that I have no experience with the proposed solutions below, so they might as well be unsuitable.

It should generally by possible to attach a flow meter to the hose of the bladder. There are rather small versions out there used for example for gardening or laboratory purposes. I am not sure about the minimum flow requirements and the accuracy of those things, but there might be a variant usable for low flow/volume purposes. Camelbak seems to have made such a flow meter a while ago, but I am not sure if it has been discontinued. The available online reviews are mixed.

Another alternative relies on pressure measurements inside the bladder. The principle has been commercialised and is available e.g. at https://www.hydratemate.com/. There are some requirements on the bladder construction, so check that before testing. Also, the measurment unit has to be attached to the bladder directly. So you either have to pull out the bladder to get a reading or you have something like an app installed on your phone that shows the reading.

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I use a bladder when mountain biking because it keeps the weight on me rather than on the bike, and has no risk of bouncing out of a bottle cage - plus bottles get covered in mud and/or get very cold. I tend to under-hydrate because I drink when it fits the riding conditions or when I stop, and the slow flow compared to a bottle means I don't drink much each time.

So I've learnt to get a feel for the weight of the pack - when I stop, I reach behind me and weigh the pack in my hand. I'm not trying to get a number just a feeling - has enough gone? As well as weight, which can change due to other items, the sloshiness (it's a word now) of the contents is a useful sign. That loose feeling of the water moving around is more easily assessed by taking the pack off and tilting it in 2 hands, or by opening it and reaching into the compartment with the bladder, but you can get a rough feel with a hand behind your back. If you're stopping to get a snack/tools/jacket out, feel the bladder and/or whole pack then.

I suggest you try it out yourself with the use of a luggage scale for calibration: Use you pockets for snacks etc. to avoid confounding factors, feel the weight, then take the pack off and weigh it. I don't suggest habitually carrying scales.

The other thing you can try, at home, is filling the bladder to 1/4, 1/2, 3/4 and brim full, then putting it in the pack with your other stuff and feeling the weight/balance.

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you can keep the lid at the top of your pack and get a long small diameter pole and from the hardware store and use it as a dipstick

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  • Clever idea but I'm not sure it would work - the water level in the bladder will vary wildly depending on how compressed it is. The only way to get a good reading from a dipstick would be to take the bladder out of the backpack, by which point you can see how much is left.
    – aucuparia
    Jan 25 at 10:12

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