Baseboard
Water at the baseboard travelled to get there.
A wet shoe moulding is rarely the start of the story. Water follows the lowest edge it can find, including the gap under drywall.
Photograph the run before you mop it all away.
Note which wall, how long the wet edge is, and whether it is cold, warm, or dirty.
Ask whether a fixture above or beside it was used.
A shower, a washer, or a heater closet next door changes the suspect list.
Do not pull the baseboard as a test.
You can make a small leak look like a large one and lose the stain map.
Questions people ask
Is this always a slab leak?
No. Walls, patio doors, and overflows also wet baseboards.
Can I run a fan along the trim?
After the source is controlled. Drying first can hide an ongoing leak.