I come from a triathlon background, so I'm pretty much hard wired now to drink every 10 to 15 minutes or so while on the bike, from a water bottle. It's second nature now. Carry extra water in my panniers, find that it forces me to stop every couple of hours to refill bottles. Makes for a nice break in the riding. I find that a pack on my back tends to aggravate a shoulder problem, so I avoid it. Must admit, the idea of ice cold water throughout the day is very tempting though.