Anytime you go out for an extended walk or hike you have to make sure you have plenty of water with you. Carrying a water bottle isn't always ideal if you want to have your hands free. A hydration pack is a good way to make sure you have plenty of water and carry it comfortably with you while having your hands free.
This pack can be tightly secured to you allowing you to run a marathon if you wanted. With anti-slosh technology you don't have to worry about the water sloshing around on your back while you walk.