Hidden compartment
It backs into my head when the boat leans.
Grumpy, I chased the "Mystery Water In the Head When I Heel" for a couple of years.
In the bottom of the starboard cockpit locker is an access panel with the pressure water pump, under the non-removable floor it is mounted on is a "Blind Compartment" with no drain to the bilge.
On my boat there was a gap in the tabbing at the aft end of the pump compartment floor which would let any water accumulate in the blind compartment until it was full enough and when you went sailing the heel angle would put the open spot in the tabbing down far enough to let the water run out. it would then slosh around in the pump compartment until it went into the head through the holes that the head plumbing passes through.
Then you would find a cup or two of water on the head floor.
The "Fix" was to open the tabbing at the aft end of the pump floor and use an electricians extension drill bit to drill a hole at the forward inboard corner of the blind compartment to let the water reach the bilge.
You run the drill bit along the inside of the hull and drill below the aft inside corner of the head below the head floor.
The mystery took two years to solve and the fix took an hour and a half including a trip to Home Depot for the drill bit.