First, buy a replacement "Warning Buzzer Speaker Parking Aid Fit For VW Beetle Golf Audi Skoda 8E0919279~ (Fits: Skoda Superb)" @ around £7 from an online auction house.
Then, carefully prize the buzzer unit off with a large screwdriver, breaking off the plastic rivets & carefully pull unit out into the daylight.. Then unplug the electrical connector & throw the dead buzzer unit & broken rivets away.
Next, reconnect the wiring plug onto your new buzzer unit & check that your rear sensors & screen graphics have now burst into life again!
Finally, remount the buzzer back where it came from with a dob of hot glue or strong double sided tape or similar.
Tidy up, drink tea.👍
I think that the "water under the car" thing is probably a complete red herring. EVERYTHING to do with the rear sensors goes down when the very "cheap & cheerful" buzzer unit fails.
The hardest job is always locating the buzzer unit.
(FYI, anyone has a Superb mk2 2010 estate, stand at the back of the car, open the boot & prise down the top right hand corner section of head lining. The buzzer unit is tucked up in there! (Not as previously searched for inside the A,B,C & D-Posts & next to the central rear roof aerial))