As to water at the bottom of the lift shaft, this could be due to the grey water drain system backing up from the FWD drain mast or pipe blockage upstream of the mast. When this happens, water from the fwd lav sinks and galleys fill the drain pipes and they back feed up through the floor drains located in the galley cart stowages and lift compartment( as they are the lowest open points in the system). This is usually picked up by the cabin crew as wet carpets around the galleys. It could be due to the fore mentioned ribbon heater failing. Usually the rubber tube ruptures as it expands with ice and you get waste water spilling into the wing to body fairings and a dirty stain down the belly panels. In bad cases there is an ice build up on the exterior of the panels on arrival. We check the ribbon heaters by spraying the ribbon heater thermostat with freezer spray on A checks.
On two of our aircraft, the galley system installed has a "drain down" cock next to the water isolation cock in the galley. It is for maintenance use only and is supposed to have a flap covering it with a screw securing it. Twice, in my experience, the cock has been opened during flt allowing the pressurised potable water to flow feely into the drain system. This has two effects, one is that flight runs out of water within a couple of hours and the second is that the drain system is deluged and back flows out of the floor drains. On one occasion water ingressed into the MEC and effected a couple of LRUs due to a silted up drip tray drain tube.
Of course, the lift shaft water could just be from a cart spillage and a blocked floor drain. It is pretty mucky in there.
Apologises if this info has already been mentioned, I did not go back over all the pages of this thread.