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Hydration bladders: fit your pack, then fill and clean

By the Life in Good Form editors. Updated 2026-10-18.

We research products from makers' specs and health sources; we do not run hands-on tests. Links to Amazon may earn us a commission at no cost to you. How this works.

Start with the pack you own

A hydration bladder, or reservoir, is the bag inside a hydration pack. If you already have a pack or running vest, measure its reservoir sleeve and check how it holds the bag. HydraPak says the Contour's universal hanger works with clips, hooks and loops in packs from Osprey, CamelBak, Gregory, Dakine and EVOC, and that the Velocity's hanger fits vests and packs including Salomon, Nathan, Osprey and CamelBak.

Compare the flat size to your sleeve: 14.6 x 7.5 in for the Contour 2L, 12.6 x 6.0 in for the Velocity 1.5L and 15.0 x 8.7 in for the Big Zip EVO 2L. Shopping for a whole pack instead? See our hydration pack guide.

Capacity and weight

The Contour 2L and Big Zip EVO 2L each hold 2 liters, or 70 fl oz. The Velocity 1.5L holds 50 fl oz. Empty weights are 125 g (4.4 oz) for the Velocity, 142 g (5 oz) for the Contour and 171 g (6.0 oz) for the Big Zip EVO, per the makers. Water itself weighs about 1 kg per liter, so a full 2 L reservoir adds about 2 kg to your load.

Platypus also lists 1.5 L and 3 L Big Zip EVO sizes and a 2 L lumbar version, and HydraPak lists 2 L and 3 L Velocity and 1.5 L lumbar and 3 L Contour sizes.

Opening, valve and hose

All three open across the top with a slide closure, which makes adding ice and drying easier than a small screw cap. Platypus says its SlideLock slides both ways and has a pincher grip for one-handed filling, and its high-mount quick-disconnect lets you detach the drink tube without digging into the pack. HydraPak's Plug-N-Play connector separates the tank from the tube for filling and cleaning.

For shut-off, Platypus lists a leak-proof shut-off valve and the HyFLO self-sealing bite valve with a larger 5/16 in drink tube. HydraPak's Comet bite valve self-seals, and the Contour adds a tube magnet to hold the hose in place. Platypus says to compress its valve only lightly, 30 to 50 percent, because biting too hard cuts off flow.

Cleaning and freezing

Platypus says to hand wash its reservoir with warm or hot soapy water, and lists a baking soda and lemon juice method for deeper cleaning. It says the Big Zip EVO's semi-rigid center baffle makes cleaning and drying easier, and that embedded silver-ion protects clean water from mold and bacteria. HydraPak describes its reservoirs as easy to clean, and its Contour can be reversed for drying.

Both makers say you can freeze a reservoir with water in it if you fill it no more than three-quarters full, because ice expands and can split it. HydraPak adds not to drop a frozen reservoir, since an impact at low temperature can split it.

Materials

Platypus says all Big Zip EVO materials are certified taste-free, BPA-free, BPS-free and phthalate-free, lists a polyurethane and polyethylene film with a silicone bite valve, and says it is made in the USA of US and imported materials. HydraPak lists TPU, ABS, POM, PP, EPDM, silicone, 304 stainless steel and TPU-coated nylon fabric, and calls the Contour BPA and PVC free.

Drink enough on hot days

A reservoir makes sipping easy, but it does not tell you how much to drink. MedlinePlus says to drink plenty of fluids every day and to drink more when the weather is hot or you are exercising. It lists sweating from exercise in hot weather as one way people become dehydrated. For long or hot outings, see our electrolyte tablets guide.

Warranty and returns

HydraPak's Beyond Lifetime Guarantee says it will repair or replace an item for free if it fails because of manufacturing or materials. Platypus says most of its products are backed by a limited lifetime or 3-year warranty and points to its warranty page for details; we did not confirm which applies to the Big Zip EVO. Check the Amazon seller's return notice before you order.

What to look for when you buy

Questions people ask

Will any hydration bladder fit my backpack?

Not always. Check your pack's sleeve size and hanger. HydraPak says its Contour and Velocity hangers work with clips, hooks and loops in many brands' packs and vests.

Can you freeze a hydration bladder?

Platypus and HydraPak both say yes, if you fill it no more than three-quarters full. HydraPak says not to drop it while frozen.

How do I clean a hydration bladder?

Platypus says to hand wash with warm or hot soapy water and gives a baking soda and lemon juice method for deeper cleaning. Wide slide tops make drying easier.

What size hydration bladder should I get?

Match the pack first. These come in 1.5 L (50 fl oz) and 2 L (70 fl oz), and both makers sell 3 L sizes for longer days.

Why is my bite valve not flowing?

Platypus says biting too hard can cut off flow on its HyFLO valve and suggests compressing it only 30 to 50 percent. Also check that the shut-off is open.

Sources

• Contour 2L (hydrapak.com), HydraPak
• Velocity 1.5L (hydrapak.com), HydraPak
• Big Zip EVO Reservoir (cascadedesigns.com), Platypus (Cascade Designs)
• Dehydration (medlineplus.gov), MedlinePlus

Sources checked 2026-10-18.