These are good videos produced by the USGA demonstrating how the rules apply to situations:
USGA Video: Ball Lost or Out of Bounds
USGA Video: Water Hazards
USGA Video: Provisional Ball
What's the Ruling?
If my ball crosses a water hazard (not a lateral water hazard), hits the bank on the other side,
and rolls back in, I can drop over there on the other side, right? After all, I crossed the hazard.
A. No. The point is not that you crossed the hazard, the point is that, when all is said and done, you
have ended up in the hazard. Once you’re in a water hazard, your relief options under Rule 26 all
require that you drop behind the hazard and hit over it again.
What’s the ruling “My approach to the green struck a club left behind by a player in the group ahead?”
Do I get to:
1) Place my ball where it hit the club w/o penalty
2) Play the ball where it came to rest
3) Get a do-over from the place where I hit my last stroke w/o penalty
Rule 19-1 says, the club left near the green is considered an outside agency. So 2 is the answer – your shot must be played where it lies without penalty, because you never cancel a stroke made from off the putting green that strikes an outside agency, moving or not.
Learn more about the rules of golf: USGA Rules of Golf