Did you taste it?
Most unlikely to be sea water. Most causes are either rainwater getting in through either the toe rail or stanchion bases or in my case a leak on the cold water pipe at a tee just from the aft tank.
Dry the area off and sprinkle the bilge with talc and that should indicate where the water comes from.
It can take many months to trace but if you find it as a leak on a stanchion or toe rail fixing then Captain Tolleys Creeping Crack Cure (No jesting) seems to work quite well.
And having just re read your post saying that there is only moisture, no water I’d suggest it is probably condensation forming on the cold keel bolts and nothing to worry about at the moment.