Water Hazard - Prohibited Actions

Ball played as it lies - (Water Hazard)
Most golfers know that if their ball lies in a hazard they must not touch the ground in that hazard, or the water if it is a water hazard, with their hand or club. 
Many golfers also realise that they must not touch or move any loose impediment (e.g. stones, branches and dead leaves) lying in or touching the same hazard, unless it is with the forward movement of their club as they make their stroke. 
However, there has been many an argument or discussion amongst the community in regards whether there is a penalty or not for touching anything that is growing with a practice swing, their backswing, or the forward movement of their club before it strikes the ball, even when their ball is lying in a hazard.  The short answer is no there is not a penalty.

The Note to Rule 13-4 clarifies;

At any time, including at address or in the backward movement for the stroke, the player may touch, with a club or otherwise, any obstruction, any construction declared by the Committee to be an integral part of the course or any grass, bush, tree or other growing thing.
Of course, the player must not do anything to improve their lie, area of intended stance or swing, or line of play by moving, bending or breaking anything growing, because this would be a breach of Rule 13-2. 

In a playoff in the Verizon Heritage PGA event in 2010 between Jim Furyk and Brian Davis’.  Brian Davis hit his ball near the 18th green, rolled down a slope and into a hazard adjacent to the putting surface.  The hazard had twigs, grass and other debris in it.  
During his backswing, Davis believed that he had touched blades of grass or reeds that were growing in the hazard and called a penalty on himself, forfeiting the victory. 

Davis was the only one who saw the violation, and slo-mo replays were used to determine if he was correct before the penalty was assessed.  It was assessed and he lost..
Watch the video of the infringement at Brain Davis; Loose impediment