The S5 has a cover over the usb port but interestingly, not over the 3.5mm headphone jack. I can attest that I spent all day in the rain with my S5 out of my pocket and taking pictures in said rain, and it performed great. That said, we have had a couple users on our S5 sister forum who reported issues where, after getting the phone wet (one dropped his in a pool, the other caught in a downpour) the headphone icon was stuck on in the notification bar, with no actual headphones attached. In both cases, the issue/icon went away on its own after about a day of normal (dry) use, with no residual problems to report since.
Of course I've seen quite few of the S5 water tests on YouTube, and they all passed with flying colors.
I did find it odd that this open headphone jack doesn't cause more problems than it does. I'm not complaining though. LOL
The usb cover on the S5 is one of the "cons" IMO, but it works as advertised, so I've learned to deal with it.
S5 tap'n