Today's discovery is a tiny pool of water on the kitchen tiles (not that unusual as sometimes water gets splashed around a little when doing the washing up)... that's coming from the corner of the under-the-sunk cupboard... that's the result of a shallow pool coating the bottom of the under-the-sink cupboard.
After emptying and mopping out the cupboard, it appears that the water is dripping from the cold and hot water pipes. And following the pipework further, it's coming from the kitchen tap. Which of course is right at the back of the cupboard behind a mess of pipework.
I'm fairly sure the pipework isn't leaking, but rather I think it's actually the spout for the tap - it's a swivel spout on a single post with a combination mixer tap on top. The water meter doesn't show any flow when the tap is off, and also if the tap's been off for a while then there's a delay before any water comes out the spout.
In any case this qualifies as "the landlord's problem," and as it's not leaking when the tap's off it can wait until the morning.