Ok I'm still think fridge water, evan if you don't have that fridge. When they hook up a fridge they run 1/4" copper or plastic pipe and hook it into a water line somewhere with real mickey mouse fitting that just screws into the side of the water pipe. They run this pipe where ever, thru cupboards, under cupboards or where ever. So just have a look around for that.
After that this could be anything from leaking plumbling to a leak in outside wall to a leak in the roof. What is above this area?