Best way I've found is open the app, and either start the video then submerge the phone and video, or use the camera button to snap away.
I've found it only works when fully submerged. If only half the phone is under then the water presses buttons, however when it's fully under its fine. Must be that the water is acting as your fingers so when only half or part submerged it just presses there, however when it's completely under it doesn't quite know where to press, so it doesn't. If that makes any sense haha. My advice. Fully submerge and either start recording before, or for pictures, use the shutter button on the side
Attached is a quick one I just took
Sent from my D6503 using XDA Free mobile app