...with water pistols.
It has to be. We've eliminated all the other possibilities so whatever remains, no matter how improbable, must be the truth.
The side has been off the bath for a year: all we need to do is work out where the fuck the water's coming from.
It's usually a tiny drop sitting on top of the compression joint between the hot water pipe and the tap. We've tightened the joint a few times and thought we'd got the bugger. But last week, after I'd had an arm in there stuffing insulation against the outside wall / concrete floor, suddenly the whole damn area was wet - underside of bath, nut holding tap unit tight to underside of bath, much calumnied compression joint just below.
By today, back to normal. Slight wetness.
It can't be a mere loose compression joint, cos whenceforth the post-insulation splurt?
It can't be water sitting on the bath top making it's way under the tap unit (two-hole monoblock jobby with shower hose) - we've tested by drying all, flooding there, testing.
It's not the weight of someone showering in the bath combined with the above.
It can't be condensation - it's a copper hot pipe, and there are plenty of bone dry cold pipes right next to it.
It's not exposed to general splashing - way in under the bath and high up. And besides, consistent local splashing?
It's not even a loose overflow fitting leaking under pressure of the shower spray: we've tried that too.
It's none of these things. I've been on my hands and knees with bits of tissue for months. The plumbers are baffled. The handyman's baffled.
Mumsnet, I turn to you. 