Stoves and water

Hydration bladder

Also called reservoir, water bladder, hydration reservoir

What is a hydration bladder?

A hydration bladder is a flat water reservoir carried inside a pack with a drinking hose routed over the shoulder. It holds 1.5 to 3 liters, packs flat against your back and lets you drink without stopping or taking the pack off.

Common sizes: 1.5 to 3 L
Strength: Drink without stopping
Weakness: Invisible level, cleaning, hose freezing

The one thing it does perfectly

A bladder solves one problem completely: drinking without stopping. The hose clips to your shoulder strap and you sip whenever you think of it, which in practice means you drink far more over a day than you would if every mouthful required taking the pack off. That's why nearly every day pack now has a dedicated sleeve and a hose port.

What it costs you

The costs are all in maintenance and awareness. You can't see how much is left, so people routinely misjudge it. Filling one means opening the pack and often unpacking around it. And a bladder left wet in a warm cupboard grows mould with impressive speed, which is the main reason people abandon them.

Why hoses freeze first

Cold weather adds a specific failure. The hose is thin and exposed, so it freezes long before the reservoir does, and once it's blocked the water in your pack is unreachable. Blowing the water back into the bladder after each sip is the standard fix, and insulated hose sleeves help.

What this means when you're choosing

A wide opening or slide-top, which is what makes cleaning practical
A shut-off valve at the bite valve, for packing without leaks
Hose routing on your pack, since a hose that isn't clipped down swings

Hydration bladder vs Soft flask

	Hydration bladder	Soft flask
Capacity	1.5 to 3 L in one place	250 to 750 ml each, so several
Knowing your level	Invisible until you take the pack off	Visible on your chest
Freezing	The hose goes first, long before the reservoir	Nothing thin to freeze
Refilling	Usually means taking the pack apart	Pull it out, fill it, put it back

Which to pick: A bladder when the carry is long and volume wins. Flasks when you want to see what you have and refill without stopping properly.

The common mistake

Not knowing how much is left

A bladder is invisible in your pack, so people either run dry unexpectedly or carry water they never drink. Learn what a given number of sips is worth, or pull it out at breaks. In freezing weather, blow the hose clear after every drink.

Common questions

How do I stop a hydration bladder growing mould?

Dry it completely between trips, which is the whole answer. Prop it open with a clean utensil or a purpose-made hanger, and store it in the freezer if you can't get it properly dry.

Why does my hose freeze before the bladder?

Because it's thin, exposed and full of still water. Blow the water back into the reservoir after each drink, tuck the hose inside a jacket, or use an insulated sleeve.

Where this comes up

Guides on Tom's Hiking where hydration bladder changes which product is right for you.

Going deeper

More in stoves and water

Canister stove

A canister stove screws directly onto a sealed cartridge of pressurised isobutane-propane. It lights instantly, simmers well and needs no priming, which is why it's the default backpacking stove almost everywhere fuel canisters are sold.

Integrated stove system

An integrated stove system pairs a burner with a matched pot that locks on, usually with a heat exchanger ring on the base. It boils water faster and uses less fuel than a separate stove and pot, at the cost of versatility.

Regulated valve

A regulated valve holds a stove's fuel pressure steady as the canister empties or cools. Without one, output drops off through the canister's life and falls sharply in the cold; with one, the flame stays consistent much further down.

Isobutane-propane blend

Isobutane-propane is the fuel blend inside standard threaded backpacking canisters, usually around 80 percent isobutane and 20 percent propane. Propane provides cold-weather pressure, isobutane provides most of the burn time.

Hollow fiber filter

A hollow fiber filter passes water through a bundle of tiny straw-like tubes whose walls are perforated with pores around 0.1 to 0.2 microns. It's the technology in almost every modern backpacking filter, and a single freeze can destroy it invisibly.

Micron rating

A micron rating states the largest particle a filter lets through, in microns. Backpacking filters are typically rated 0.1 or 0.2 microns, which stops bacteria and protozoa. Viruses are around 0.02 microns and pass straight through.

Flow rate

Flow rate is how fast a filter delivers clean water, usually quoted in liters per minute. The advertised figure is measured on a brand-new filter with clean water, and real flow drops as the element clogs with sediment.

Backflushing

Backflushing pushes clean water backwards through a filter to dislodge the sediment clogging its pores. It's routine maintenance on a hollow fiber filter, and it's the difference between one that lasts a season and one that lasts years.

Purifier vs filter

A filter physically strains out bacteria and protozoa. A purifier also deals with viruses, which are too small to strain, using chemistry, UV light or a much finer element. Most backcountry hiking needs a filter; international travel often needs a purifier.

Soft flask

A soft flask is a collapsible bottle, usually 250 to 750 ml, carried in the front pockets of a hydration vest. It shrinks as you drink so it doesn't slosh, and you can see exactly how much water you have left.

Bite valve

A bite valve is the silicone mouthpiece on the end of a hydration reservoir's drink tube. It stays shut until your teeth compress a slit in it, then self-seals when you let go, so water only flows while you are drinking.

Quick disconnect

A quick disconnect is the two-part coupling in a hydration hose that lets you unclip the tube from the reservoir without threading it back through your pack. Both halves usually self-seal, so you can pull the bag out to refill and neither end drips.

Hard-anodized aluminum

Hard-anodized aluminum is aluminum whose surface has been grown into a thick, very hard oxide layer by an electrochemical bath. In cookware it gives a pot that spreads heat far more evenly than titanium and resists scratching far better than bare aluminum.

Last reviewed August 13, 2026. Back to the glossary