I have a recurrent problem with water apeparing under my bath tub which then leaks into the ceiling of a downstairs neighbour.
It has happened on and off for the last 4 years.
On the occasions when it appears to have been 'fixed' different issues have been responsible, eg the trap, sealant needing replaced, leaking tap connector etc.
But this time no one seems able to fix it. Plumber attended this week and said it was a hot water pipe leak which he believed he'd resolved (I believe with a new washer??)
However the next day we put a tray under the bath and it was relatively full after 2 showers.
Prior to this we put the same tray under the pipes at the tap end of the tub overnight and noticed water had appeared. (This led to diagnosis of leaking hot water pipe.)
The only issue I can see is small drops of water 'beading' on the underside of the cold and hot water pipes. But this appears to be moisture -- I think -- as there is a fair amount of condensation on the pipes.