I try to avoid it, even wth an aero bottle. Hydrate well days before, and the morning of, and just before you go off, and you should be fine. SHOULD is the operative word here, as this past sunday, with temps and humidity the way it was, I (in hindsight) should have had water as I needed my first drink around mile 4 (only 21 to go!!). I would say it is a matter of your history (have you gone without water in the past), your hydration status, and the wether conditions.