I know that trying to solder a joint which has any water in it may well
fail - however what about compression joints? Do these need to be
completely dry before making the joint?

No, compression joints can be done whilst wet. Good job really when we added
a new working stopcock to my system that didn't have one...

Don't bother with jointing compounds or PTFE. Compression joints should be
made without either, so you rely on the metal to metal bond, rather than
some organic compound that might break down over the decades.

Christian.

P.S. I have successfully soldered pipes (15mm, never tried 22mm) with
containing water. Drain off what you can (it wicks away nicely with lots of
bog roll). Then use lots of water soluble flux and a f*cking big torch. No
guarantees. I've never used the bread trick, but am told it can work.