Water-filled Bunker

A competitor's ball was seen to splash into deep casual water in a bunker, but it is not visible. However, it is obvious that there is nowhere that the player can drop a ball in the bunker that is not covered in water and is not nearer the hole.

Question 1:
a) Does the player have to find their ball if it is known to be in the bunker?
b) May the player take relief from the casual water, without penalty, by dropping a ball outside the bunker?
c) If the player finds the ball in the bunker may they take relief by dropping a ball at Y, which is the point where the water is shallowest?

Answer 1:
a) No, Rule 25-1c.
b) No, but see Question 2 below.
c) Yes, providing that this is the point nearest to where the ball lay that is not nearer the hole and affords maximum available relief from the condition.

If it is known or virtually certain that a ball that has not been found lies in casual water in a bunker, the player may substitute another ball, without penalty, and take relief as prescribed in Rule 25-1b(ii) (a).