A wetting unit for wetting a surface of one of a first and a second continuous water-soluble films to be coupled and sealingly joined to each other so as to delimit therebetween recesses containing dosed quantities of at least one fluid composition for producing unit dose articles. The wetting unit is configured to wet only surface areas of one of the first and second continuous water-soluble films which are to be joined to the other of the first and second continuous water-soluble films.