Hardly anyone knows all the rules so its likely we've all transgressed and benefitted (or not) from a situation where we shouldn't, that's not cheating in my opinion and when it happens we hope we learn the correct action in the future. I just worry when people play regularly in competitions and don't even know the very basics and, like I had last week, someone who acknowledged that I do study the rules and that he didn't, but argued vehemently that if you play a provisional and find your first ball in a water hazard you have to play the provisional come what may! How many others will he misadvise
To be fair to him, this is not always an easy set of rules to interpret. If you know or are virtually certain that your original ball has gone into a water hazard you should proceed under Rule 26-1, which states:
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 the absence of knowledge or virtual*certainty that a ball struck toward a water hazard, but not found, is in the*hazard, the player must proceed under Rule 27-1.
If a ball is found*in*the water hazard or if it is known or virtually certain that a ball that has not been found is in*the water hazard (whether the ball lies in water or not), the player may under penalty of one stroke:
a. Proceed under the stroke and*distance provision of Rule 27-1 by playing a ball*as nearly as possible at the spot from which the original ball was last played (see Rule 20-5); or
b. 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
c. 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.
(Prohibited actions when ball is in a hazard - see Rule 13-4)
(Ball moving in water in a water hazard - see Rule 14-6)
PENALTY FOR BREACH OF RULE:
Match play - Loss of hole; Stroke play - Two strokes.
So proceeding under Rule 27-1 is already an option in 26-1.
If there is any possibility that the ball has not gone into the water hazard, you may play a provisional ball under Rule 27-2, but if the original ball is found either inside or outside the water hazard within 5 minutes, it is still the ball in play and the provisional ball must be abandoned.
So quite a lot depends on what you say or do.