Avoid deep puddles. That's the only thing you need to worry about. At least for my Injen CAI with the filter tucked in below the drivers headlight it is hidden behind the bumper cover and the filter doesn't get wet in there with it being surrounded by plastic on all sides. I have had this installed for close to 4 yrs without any issues.
A little bit of water is no big deal. I've ran my EM1 at highway speeds in a downpour with the filter right in front of the passenger tire getting splashed (no fender liner) for a couple of hours and the engine was fine. If that didn't lock the engine up, a tiny bit in your intake tube isn't going to hurt anything.
People get so paranoid over a bit of water in their intake, it's ridiculous.
A little bit of water will not hurt anything and will get rid of carbon buildup but a lot of water will cause hydraulic or hydro lock (there I changed it:grin.and bend or break things but that takes a deep puddle or river.
I am use to round engines on planes and thats what we call it and trust me we get it on the lower cylinders hence the reason to pull the props through 15 blades on that bird in the background.:smile: http://www.youtube.com/watch?v=dBXP8NJWj3s