Purity: Dryness of the Wiping Area
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 255
The area to be wiped must be dry; if it is wet to the extent that the wetness of the hand has no effect on it, the wiping is invalid. However, there is no problem if the area to be wiped is merely damp, or its wetness is so little that it becomes absorbed in the wetness of the hand.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)