I have read on the reddit that drones can fall out of the sky if you fly them over water. Are there guidelines for how to prevent this happening somewhere?

I'm not sure why, but people have an unreasonable fear of water with drones.  Of course if you fly it down into the water, you are going to likely have a total loss and unlikely to recover it.

Just don't fly it close to the surface and there will be no more of a chance of crashing than when you are over land.

KlooGee Posted at 7-4 14:15
I'm not sure why, but people have an unreasonable fear of water with drones.  Of course if you fly it down into the water, you are going to likely have a total loss and unlikely to recover it.

Just don't fly it close to the surface and there will be no more of a chance of crashing than when you are over land.

I hardly think that, having spent nearly 3 grand on a piece of kit, trying to figure out the safety margins constitutes an unreasonable fear of water.

CuAnnan Posted at 7-4 14:56
I hardly think that, having spent nearly 3 grand on a piece of kit, trying to figure out the safety margins constitutes an unreasonable fear of water.

It is unreasonable for someone to say that drones fall out of the sky if you fly over water.  

It is reasonable to try to understand safety.   As I said, just make sure you don’t fly close to the surface, then you’ll have no problems.  

Drones use several systems to understand their environment around them and where they are in space.   If you understand these different systems and understand how they each affect the drone’s performance, it will give you some level of comfort.  
- GPS:  It would not be affected by water vs land.  
- Compass:  It would not be affected.  
- Barometer: It would not be affected.  
- Inertial measurement system:  not affected
- Obstacle avoidance: not affected
- Downward visual positioning system: this is the one that you need to understand and how it could affect you.  If the water is glasslike or very reflective, it may not be able to see the surface and understand how high above it you are or if you are moving in relation to it.  

This last point is exactly why I originally mentioned to stay well above the surface and you’ll be fine.  If you are well above the surface, then the downward VPS is not utilized at all, so will not affect the performance of your drone.  And yes, I still think people have an unreasonable fear of flying over water just randomly causing drones to fall out of the sky.  That is just not correct.

My longest flights have all been over salt water, in fact most of my flights would be over salt water at some point.
My drones have yet to be endangered by a tree or building whilst over the sea, lol.
More seriously, yes there would be no second chances and no rescues of a downed drone, it would be virtualy pointless even if it were possible, but I would normally be at more the 10m MSL.  
If you go down low you need to be ready to give it full throttle instantly if you see any descent or even think is descending.
My lowest point, 1 or 2 ft with a Phantom 3, for a stationary shot of the seaweed on a buoy.
Would I try that with a landing protected Mavic? No but I would guess I have had a Mavic down to 3ft and crept it forward to get a view up a pipe.
Would I move at speed at such a height, not the slightest chance, all transits would be at 10m+  and more likely around 20m.
Have I had any scares yes, one real one, with a Mavic Mini or a Mini 2, that I think started to descend at the end of a traverse that was flown at a height of maybe 5 to 8m and ended over shallow water.
The Mavic Mini and or the Mini 2 have been reported to occasionally descend at the end of a speed run and they have been reported to dislike shallow water so I had the worst of both worlds there. I gave it full throttle and am still flying the drone.

Total flown distance? Ignore what appears in my profile, I do not sync logs. According to my log book and for flights where the logs record a distance travelled that is greater than 8m, 577.76km, approx 1100 flights.

My list of logs is also missing a few entries as I have lost logs, notably for my P3, I did something stupid I guess, and NONE of my Mini 2 flights are included in that as they do not yield a distance travelled entry in their csv, I need to do a bit of coding to work those numbers out.

Hello there CuAnnan. Good day and thank you for reaching out.  Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread on How to Fly Safely Over Water. Thank you.

https://forum.dji.com/forum.php?mod=viewthread&tid=181878

I've flown across a lake with the Mini One at a height of 2 metres above the surface, with no issues. And larger bodies of water (reservoirs) numerous times, with no issues.  Water is not the problem.  It's how close to it you get that counts.  The downward sensors of your drone can become confused by reflections and ripples and  thence unable to compute safe height.  If you remain calm and in sight of the drone, and manoeuvre carefully, you should be OK.

DJI Stephen Posted at 7-4 19:56
Hello there CuAnnan. Good day and thank you for reaching out.  Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread on How to Fly Safely Over Water. Thank you.

https://forum.dji.com/forum.php?mod=viewthread&tid=181878

Hi Stephen,

And again you post this outdated link!!  why ?

FlyApp drones cannot disable the VPS bottem sensor!!

And the vision positioning is not turned off automatically flying over water!
And what do you mean with "...affected by the accuranct range, an accident might happen" ?? It is so wrong!

I fly many times low over water, VPS bottom sensor does sense alway the correct height.Only when flying slow or hovering low over streaming water the VPS downward sensor gets sometimes "confused"....
Well, just my experience flying many many flights low over water.
And, analyzing logs, you can see that the vision is not used for positioning when the GPS signals are oke. (see the manuals as well ....)

Best for DJI is to change the autolanding protection such that it will automatically turns off with some speed in any direction! This has caused many wet drones....

Cheers
JJB

DJI Stephen Posted at 7-4 19:56
Hello there CuAnnan. Good day and thank you for reaching out.  Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread on How to Fly Safely Over Water. Thank you.

https://forum.dji.com/forum.php?mod=viewthread&tid=181878

Just a reminder that when flying above the water, the vision positioning function will turn off automatically
It's disappointing that the moderators here spread misinformation like this.

I have read on the reddit that drones can fall out of the sky if you fly them over water.
Reddit isn't a good place to find accurate and helpful information on flying your drone.
Flying over water is just like flying over land, except there are less obstacles to hit.

DJI Stephen Posted at 7-4 19:56
Hello there CuAnnan. Good day and thank you for reaching out.  Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread on How to Fly Safely Over Water. Thank you.

https://forum.dji.com/forum.php?mod=viewthread&tid=181878

DJI Stephen,

I agree with all the others, it is very disappointing that you are providing completely incorrect information!  I would expect better information to be provided!