Dear readers,
In order to take relief for a ball in a water hazard, the Rules require that it must be “known or virtually certain” that your original ball is in the hazard. Judging from recent questions I have received, there seems to be confusion about the meaning of that terminology. There is a Decision that does a good job of clarifying that phrase. I believe you might find this explanation helpful, so I am reprinting it below:
26-1/1 Meaning of "Known or Virtually Certain"
If a ball has been struck towards a water hazard and has not been found, the term "known or virtually certain" indicates the level of confidence that the ball is in the water hazard that is required for the player to proceed under Rule 26-1 [Water Hazards]. A player may not assume that his ball is in a water hazard simply because there is a possibility that the ball may be in the hazard. If it is not known that the ball is in the water hazard, in order for the player to proceed under Rule 26-1 there must be almost no doubt that the ball is in the hazard. Otherwise, a ball that cannot be found must be considered lost outside the hazard and the player must proceed under Rule 27-1 [Ball Lost or Out of Bounds; Provisional Ball].
All available evidence must be taken into account in determining whether knowledge or virtual certainty exists, including any testimony and the physical conditions in the area around the water hazard. For example, if a water hazard is surrounded by a fairway on which a ball could hardly be lost, there exists a greater certainty that the ball is in the hazard than there would be if there were deep rough in the area. Observing a ball splash in a water hazard would not necessarily provide knowledge or virtual certainty as to the location of the ball as sometimes such a ball may skip out of a hazard.
Source: United States Golf Association® and R&A Rules Limited, Decisions on The Rules of Golf. You may access the Decisions on the USGA website: http://www.usga.org/Rule-Books/Rules-of-Golf/Rules-and-Decisions/
