If I'm going to flying extensively over water I'll add the "Get-er-back" system just to be able to retrieve the airframe and maybe salvage the SD card.
If I'm just randomly flying over a portion of water (say for instance crossing a river or pond etc) I just fly normal and don't give it a 2nd thought.
The only sUAS I've lost since 2013 was one I lost in our local lake when I had a battery cell deviation error and had to pick an off-site landing area where there were no people.. Unfortunately the area was below a line of trees (a forest actually) and while descending to land lost Tx to Rx signal and initiated a RTH. My RTH settings were less than the 100 year old Oak trees and the RTH took the aircraft into the trees and it then tumbled into the lake.
I retrieved it 16 months later (they lowered the lake for dam repair) but of course it was a total loss. Sadly the SD card had some one-off photos from an event I had shot that morning that could not be re-shot. Oh well.
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