It is possible to come across models with capacity from 0.5 to 5 liters. In fact, the capacity of the hydration water bladder, first of all, depends on the distance you are going and the personal preferences of a sportsman. A volume of 2 liters seems optimal as with this option you’ll have enough water and won’t need to refill it. In addition, such a weight on your back will not be felt and will save from thirst for several hours even in extreme heat. In case if you are planning a long-term adventure, choose a model with a capacity of 3 liters. At the same time, 0.5 liters of water will be enough for a short walk.