Hydration Backpacks provide hands-free drinking while hiking or biking. Carrying fluids is the primary function of the packs in this section and all include hydration systems. Many of these packs also provide some storage space for necessities. Such packs include the reservoir, usually two or three liters in size, and some room for gear. A 2L (70 fl. oz.) reservoir is a popular, all-purpose choice. If you're often active in warm or dry conditions, consider a 3L (100 fl. oz.) reservoir. Once you've used a hydration pack, its benefits become self-evident. Since water intake is simpler with a hydration pack, you tend to drink more often, and a well-hydrated athlete is a better performing athlete.