Although the H (if working properly) has no problems flying over water...or essentially anything else for that matter, I still get a bit nervous when flying over it. I've seen too many YouTube videos of drones diving into the depths. But it seems to me that many (but not all) of those 'watery graves' videos were the result of pilot error to some degree.
So, although I try to avoid flying over water if I can avoid it, when I do I always fly over that water in the early part of the flight when the battery is still fresh (the first third of the battery) insuring that i'm back over land way before the battery is starting to get depleted. While over the water avoid aggressive flying; don't fly too close to the surface of the water and avoid anything that could splash or spray the aircraft (jet ski, speedboats, people who could splash water up for spite).
It is true that some good shots can be had from over water but in the end, for me at least, the less time over the water the better.