To drink while riding:

Grip the top (flat) part of the bar near the stem with both hands. The hands should make a complete circle around the bars, elbows should be relaxed Look straight ahead and pedal smoothly. Remove one hand from the bars, reach down with one hand and grab your water bottle. If you glance down you will tend to swerve a bit, so try to keep looking forward. Drink with the bottle slightly off to the side (corner of) your mouth. Replace bottle in cage, again without looking down.

Hope that helps