I don't think the case is as clear cut.
With my TB20, if you were to pour water all over it, nearly all of it will run straight off. No pools of water will form anywhere. All that will be left will be a few droplets, and they can be wiped off.
On the TB20, no significant water enters the control surfaces and certainly none can enter where it might block control linkages.
Obviously this is not going to work in -20C but we don't get that in the UK - not when one might be flying anyway. Since 1969, the coldest I have seen on the south coast was about -8C. The coldest I have departed in, or tried to, in the UK, was -2C and water copes with that perfectly.
Except on the wing upper surfaces IF the fuel tanks are full, in which case it just freezes into ice, due to the huge mass of the -2C fuel the other side of the aluminium sheet. That is the main reason I have found water to be useless.
I have departed from Germany in about -6C but the aircraft had been put in a hangar prior to that so it was clean.
A hangar, never mind a heated one, available to a visiting aircraft, is almost never available in the UK.