I don't really need the water at all but it prolongs the amount of time I go running. Once the run is over i still carry on so that my total moving time is at least an hour. It makes it a lot more enjoyable to be walking around with an ice cold beverage at that time. I think if I didn't carry water that it would be my frist objective to just head home immediately to get water so that's the real purpose. I don't actually need water during a single hour of exercise