Rule 26-1. Relief for Ball in Water Hazard

Ok, now let's talk about a point of rule that few golfers actually know: the relief of a ball in water hazard.

We will see in this article specifically the rule 26.1 / 2. (I put the essential part in red)

A normal water hazard is marked by yellow stakes. 

26-1. Relief for Ball in Water Hazard

It is a question of fact whether a ball that has not been found after having been struck toward a water hazard is in the hazard. In order to apply this Rule, it must be known or virtually certain that the ball is in the hazard. In the absence of such knowledge or certainty, the player must proceed under Rule 27-1.

If a ball is in a water hazard or if it is known or virtually certain that a ball that has not been found is in a water hazard (whether the ball lies in water or not), the player may under penalty of one stroke:

1. Play a ball as nearly as possible at the spot from which the original ball was last played (see Rule 20-5), or
2. Drop a ball behind the water hazard, keeping the point at which the original ball last crossed the margin of the water hazard directly between the hole and the spot on which the ball is dropped, with no limit to how far behind the water hazard the ball may be dropped; or
3. As additional options available only if the ball last crossed the margin of a lateral water hazard, drop a ball outside the water hazard within two club-lengths of and not nearer the hole than (i) the point where the original ball last crossed the margin of the water hazard or (ii) a point on the opposite margin of the water hazard equidistant from the hole.

When proceeding under this Rule, the player may lift and clean his ball or substitute a ball.

As a summary, If this happens there is a one shot penalty. You take the ball out of the water and you drop it either two club lengths away from the edge of the hazard on the line you entered.

Red stakes are used to mark a lateral water hazard. A lateral water hazards is exactly the same as a normal water hazard - and in some cases may be a different stretch of the same stream. But instead of running across a hole, a lateral water hazard runs towards it.

The rules for playing and dropping the ball are the same as for the normal water hazard except in one regard.

Special case for casual water, GUR and abnormal ground conditions - If your ball is in casual water, ground under repair, a hole or cast made by a burrowing animal (eg rabbit), you may drop without penalty within one club length of the nearest point of relief not nearer the hole.

Keep Golfing!

Sources:

Rules of Golf - Rules 26: Water Hazards

Basic rules of Golf

What happens in golf when you hit your shot into the water?