No special way. Just add water untill moist, without drowning the ants. With a soil nest you could do this just by spraying or dripping water in. With a plaster/y-tong nest you could attach some sort of reservoir to constantly feed water into the nest.
In what ? If the ants are in a tube dont put water in it, they will drown (off course) If they are in a sand nest you can spray some water on the sand (not to much) and like Phasmid said, if you use a y-tong you can attach a reservoir. (look at the gallery here at Antstore to see some farms)