The 1.5 Litre Gelert Performance Hydration Pouch will fit into any compatible rucksack (most brands) & the hose can be attached near to your mouth for easy access. The bite valve allows hands free drinking so you can hydrate yourself on the go. This is very important because it&8217;s very easy to become dehydrated while hiking or during any other physical activity&8230; & the effects are devastating. As soon as you feel thirsty you have already begun to get dehydrated. Symptoms such as headaches, nausea & tiredness are noticeable at just 2% dehydration & after becoming even a little bit dehydrated it can take up to two days before your physical & mental performance is back to normal.