I was looking for a hydration pack and came across this one:-
This hydration rucksack has a capacity of 6L along with a compartment that will allow you to carry a 1.5L water bottle. The rucksack has been designed to fit snugly around your body so that you do not have to stop if you wish to have a drink. It is ideal for walking, biking and skiing.
It is lightweight and durable and has reflective trims for added safety in poor light.