People often struggle because they naturally tilt there head back when they take a drink, as soon as they take their eyes off the road they wobble (same reason people find it hard to keep going in a straight line when checking for traffic behind them).
Try keeping your eyes on the road tilt your head slightly to one side instead and hold the bottle upside down with the nozzle in your mouth. Another trick is to squeeze the bottle to squirt the water into your mouth rather than sucking it out which can leave you a bit breathless if you take a long drink.
Practice it watching the telly and remember to keep your eyes on the screen
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