All the 'tuner' cars with ram air that I have seen having problems with water is because they are putting the ram air scoop in the front air dam below the bumper. I have seen 3 such cases (one brought to you by the local PD after they had impounded the car, gee Barney why did you think it was a good idea to hydroplane a car with 3" of ground clearance??).
There is a check valve of sorts that is available that goes in the tube and if water hits it it plugs off the inlet and draws air from under hood. If you draw the air from the top of the core support (before the radiator) this should not be a problem. IIRC Smokey did this on his NASCAR Camaro (the one they wouldn't let him run)it picked the air up at a reverse angle so inertia would carry any debris (or rain) into the radiator instead of the intake.
Of course a high mounted cold air intake could still have a problem with water, if you like fording rivers.
