Choosing the Best Running Hydration Pack
If you are doing a run of more than about 30 minutes, then it is important that you keep yourself hydrated. For runs only a little over this it is fine to just get through it, or to carry a small bottle of water. If you are running, regularly, for period of more than about 90 minutes then a hydration pack is a good idea as it is often the best way to spread the load of carrying water in a way that least inhibits your running.
Camelbak were for a long time the market leader in selling these items, but now there are a number of companies in this market providing very good kit.
Try to buy one which has wicking on the back so that you don't get too sweaty with it resting against your back.