Hydration packs are designed principally to transport water and make drinking convenient and efficient. In fact, with most hydration packs, you don’t have to stop, or even slow down, to take a sip of water; you simply grab the drink tube that’s connected to the included water reservoir (sometimes called a bladder).
There are two general types of hydration packs: hydration backpacks and hydration waistpacks. Within those groups, there are packs made specifically for different outdoor activities, including hiking, running, mountain biking, cycling, skiing and snowboarding. The common feature among nearly all of them is the included hydration reservoir that makes drinking easy.