You will KNOW if you sucked in water. Your RPMs will stutter at first. Then if you don't get out of the water or pull over somewhere shortly after, your car will simply shut off. At that point the best thing you can do is try to pull into a covered area (gas station etc). Wait till the rain settles. Whatever you do, don't attempt to crank the motor when u pull over. Check out how wet the filter is. If your lucky, the heat of the engine will evaporate any water in your motor.
How do I know this? Experience
Now equipped with an AEM bypass though.
Rich