2-bottles work great for me. And I usually only go through one. I fill one bottle with ice water and the other with only powder, Fluid Recovery" drink. I rarely finish the first bottle before the end of the ride. Then after we finish, I fill of the 2nd bottle with the powder and down it rather quickly. I presume it varies depending on how much your body requires.
Another option, although not my favorite, is the camelback system. You wear a water bladder on your back and drink through a mouthpiece connected by a tube. They're very popular in the military and can be found and most sporting goods stores.