That splash guard will protect splash from entering at the front juncture of the lid/airbox, but not from what enters between the seat and the front of the airbox which is much more an entry point.
And concerning the comment of "I went thru 3 feet of water with no problem":
No "noticed" problem. Your bike can be ingesting water and still run. And if the water doesn't have too much muck in it then it won't cause your carb slide to stick. But ANY amount of muck will wear down the cylinder, rings, piston, and bearings. I know because now I have to replace the lower rod bearing which is not a fun job. I'm just trying to save you all a headache if you occassionally go thru mud puddles.