I always train drinking water with a fuel belt, but on long runs, I plan stops to refill the belt. Then, I take in gels or sport beans (which I like because they taste good) for calories. I haven't had a problem (yet) with an event providing water, and that way I don't have to worry about the concentration of the sport drink. That is how I trained for my marathon and the half marathons. Also, if I need to stop to readjust, or go to the bathroom, or tie my shoes, I do that too. In a race, I will stop to do that if I need to as well. Just experiment. We are all different, and the nutrition is totalliy different for all of us.