A "water bladder" refers to a flexible bag made of durable material that is used for carrying water. It is often used for outdoor activities or emergencies where access to water may be limited. Full definition
You can start with the three - liter water bladder that's included with the packs. (creditdonkey.com)
The hydration pocket lets you use your favorite water bladder for on - the - go, hands - free hydration. (geekwrapped.com)
It has two accessory pockets, one main compartment, a giant front pocket, room for a massive water bladder, and a secure setup for your gun too. (geekwrapped.com)