I'm hoping this helps someone else who has drowned their drone.
My Air 2 flew into a tree, dropped to the ground and cartwheeled agonisingly slowly down a slope and into a beautiful Scottish river. Operator error - I had taken my eyes off the drone to move my own position and it drifted sideways into some small branches.

It was totally submerged in about 30cm of water. The lights on the arms remained on for about 5 seconds while it was under, then went out as I scrambled down to get it. It was probably under water for 15 seconds before I managed to pull it out. It was full of water. Here's what I did next:

1) Immediately removed the battery before I did anything else.
2) Tipped the drone this way and that to try and get as much water out as possible. Used my t-shirt to absorb as much as possible.
3) Packed the drone in the Fly More bag and headed home as quickly as I could. It probably took me 15 mins to get back.
4) Immedialy started to disassemble the drone. Removed the SD card. I didn't know what to do or where to start. Here's what I did (very helpful to have a set of teeny screwdrivers and torx bits):

• took the base off. 6 small torx screws.
• popped off all the ribbon cables (they are tiny - a small pair of tweezers helped).
• unplugged the two cable connectors that look like antennas.
• unstuck the ribbon cable at the back of the board.
• unscrewed the main board and lifted it away - several teeny philips head screws.
• unscrewed the camera and gimbal - 4 torx screws, and removed it
• removed the front arms - I was going to do the rears as well, but figured out I didn't need to do either. Best not to take the arms off. Replacing the front arms with the spring hinge is a pain (tip below)
• Put the whole lot on top of a towel on top of a radiator and left it all over night.
• Obviously I should have videod all of this but time was of the essence.
  

5) Note that the drone has moisture tell-tale stickers on it. There are DJI logo stickers on the boards that are normally white/silver. When exposed to moisture they go red. Mine were very red.
6) After leaving it overnight and checking it was all dry this morning I started reassembly, trying to remember where all the bits went.

7) The replacement of the main board is tricky. The ribbon cables are fiddly to refit as they are tiny.
8) I got it all back together and tried a new battery. Amazing. It lit up and did it's little sing-song thing, and the gimbal rotated. Fantastic.
9) Connected the controller. More amazing - it connected to the drone. An image from the camera. I could trigger photos and videos.
10) But...many many warnings. IMU needed calibrating. Gyroscope not working (30045??), invalid gimbal, gimbal not calibrated, barometer not working 30047. GPS error 30049. Gimbal unable to connect 40012 etc. Dang.
11) Removed the base plate. Looked for issues. Everything looked OK. Reassembled. Same errors.
12) It was asking for a firmware update. I did this. Weird that the controller could talk to the drone beautifully, and the firmware update went fine.
13) Drone restarted after the update. Same suite of errors.
14) Removed the base again. Re-seated the two camera/gimbal cables at the front of the board. No difference.
15) My screwdriver slipped (gently) and it pinged (very lightly) another ribbon cable on the USB socket side of the board towards the front. The cable sprang upwards. It should have been connected in place. Some more fiddling, and I realised I had not seated this cable properly.
16) It's quite a difficult one to get properly connected as you have to fight against the tension of the curve of the cable, but after some persuasion, I got that cable properly seated and it clicked into place.
17) Fired it up. Perfect. Connected fine. No errors!!!!! Ludicrous.
18) Did a little flight - everything works. GPS fine, stability fine, manouvering fine, camera, photo and video fine. Basically everything is perfect.

So there you go. If you dunk your drone, don't lose hope. I suspect salt water may be a bit of a different beast though.

Looking closely at the circuit boards, there appears to be some sort of plasticised coating over the boards which may have helped things. Also I suspect there is a safety cutout feature if the drone detects a short circuit that prevents it frying itself.

Oh, and those spring hinges for the front arms? What a pain. The key thing is to place something thin between the forward end of the black bit that the screw goes through and the aircraft body. Then, when you fold the arm backwards, that black bit will remain aligned over the screw hole and the rear locating hole, and you can then push it down into place. It looks like the factory must have a little tool to do this alignment. Without having something to hold back that black bit against the spring force, you simply can't get the holes lined up. I used a tiny screwdriver.

Drying out


Reassembly


Note red stickers denoting it’s had water in it


It lives!!!!

I’d avoid flying that anywhere it could do  damage if it crashed, that water damage could be a ticking bomb.   

Yes very good point. It will receive a thorough checking over and I only ever fly in pretty remote places (NW Scotland) anyway. I intend to be extra cautious, and have already consigned that particular battery to the bin.

sure, if it goes down next month at least you got an extra month to fly it.  as mentioned, it's just a matter of time.  sorry to hear it.

Hello there Tobers. I am sorry to read and to know what happened to your DJI Mavic Air 2 and for sharing these information with us as well. Since your DJI Mavic Air 2 crashed and was totally submerged in water.  I would recommend for you to contact our DJI Support Team at https://www.dji.com/support?site=brandsite&from=nav for full diagnosis and analysis of the said DJI if the said DJI drone is still flight worthy. Again, I am sorry for trouble and thank you.

Good job! That pretty much details what is needed to insure MOST of the water is out. The connectors are definitely made for smallish hands to assemble....stop Gary before you say something inappropriate ;-)

I think you are good as long as you take some precautions. I don't think you can ever get all the water out of the motors so before each flight manually turn all props to check for binding/sticking. I suspect that happened to my second Mini (purchased used on eBay) as both front motors became jammed by tiny metal particles inside unexpectedly. To this day I suspect water immersion by a prior owner that caused corrosion of the armatures or stator cores. You can replace a motor/arm assembly for about $35 each and I know you can do that.

As for the "plasticised coating" on the circuit boards, in the business that is called conformal coating and is very effective at preventing moisture damage.

Thanks both - most useful.

Gary I’ll definitely be keeping a very close eye on everything.

Lots of work but I'm sure glad you were able to recover it and getting it flying again.