It is possible to find special backpacks for hydration systems, but they are a bit expensive and would be ideal for runners and cyclists. If you need to take some clothes and other things with you on a hike, then you should consider a backpack with special holes and fastenings on straps for a drinking tube. In the case when you need to save money, there is no need to buy an additional backpack. Just buy the hydration bladder with a tube, put it in your backpack, take the tube out and fasten it to strap.